Thermodynamics
Thermodynamics Study of conversion of energy between heat and Study of conversion of energy between heat and other formsother forms Thermochemistry
Thermochemistry Relationship between chemical reactions and heat changesRelationship between chemical reactions and heat changes Enthalpy H
Enthalpy H Measure of energy(heat content)Measure of energy(heat content) ChangeChange Final value minus the initial valueFinal value minus the initial value Enthalpy change
Enthalpy change H kJmolH kJmol –1 –1 Heat energy transferred in a reaction at constant pressureHeat energy transferred in a reaction at constant pressure H = (H)Products - (H)ReactantsH = (H)Products - (H)Reactants Heat changes depend
Heat changes depend on conditions in on conditions in which they are which they are measured(open containers/atmeasured(open containers/atmospheric/constamospheric/constant pressure)nt pressure) Standard conditions
Standard conditions HHθθ298K 100kPa298K 100kPaInternationallInternationally agreed conditions under y agreed conditions under which a standardwhich a standard∆∆ H should be measuredH should be measured Endothermic reactions
Endothermic reactionsHeat absorbed, products have Heat absorbed, products have more enthalpy than reactants, decrease in more enthalpy than reactants, decrease in temp of surroundings(photosynthesis)temp of surroundings(photosynthesis) Exothermic reactions
Exothermic reactions Heat evolved, products have less enthalpy than reactants, increase in temp of Heat evolved, products have less enthalpy than reactants, increase in temp of surroundingssurroundings (oxidation H
(oxidation H++(aq) + OH(aq) + OH – – (aq)(aq) HH 2 2O(l))O(l))
−
− Change in physical state is accompanied byChange in physical state is accompanied by∆∆ HH Allotrope
AllotropeA structurally different form of an element in the same A structurally different form of an element in the same physical state caused by the possibility of more than one physical state caused by the possibility of more than one arrangement of arrangement of atoms(graphite and diamond are allotropes of carbon)
atoms(graphite and diamond are allotropes of carbon) G
G ‘free energy’ difference between the products ‘free energy’ difference between the products and reactantsand reactants Standard enthalpy of combustion
Standard enthalpy of combustion HHccθθ(exothermic) (exothermic) Enthalpy change wEnthalpy change when 1 mole of a substance is complethen 1 mole of a substance is completely burned in Oely burned in O22(excess(excess
air), at 298K 100kPa air), at 298K 100kPa −
− Combustion won’t take place under standard conditions but measurement of Combustion won’t take place under standard conditions but measurement of ∆∆ H must be made when the conditions at the start andH must be made when the conditions at the start and end of the
end of the reaction are standardreaction are standard −
− Energy value of fuel/food based onEnergy value of fuel/food based on∆∆ HHccsince combustion and processes that fuel/food undergoes in the since combustion and processes that fuel/food undergoes in the body gives rise to the samebody gives rise to the same
product.
product. 1 cal = 4.18J, calorific values of food important for people controlling their energ1 cal = 4.18J, calorific values of food important for people controlling their energy intake for dietary reasonsy intake for dietary reasons Standard state of an element
Standard state of an element The most stable form of the The most stable form of the element under standard conditions Helement under standard conditions H22(g), O(g), O22(g), Cu(s)(g), Cu(s)
Standard enthalpy of formation
Standard enthalpy of formation HHf f θθ Enthalpy change when one mole of a Enthalpy change when one mole of a compound is formed from its elements, at 298K compound is formed from its elements, at 298K 100kPa100kPa ∆
∆ HHf f of any element in its of any element in its standard state is zerostandard state is zero
Enthalpy of neutralisation
Enthalpy of neutralisation HHNN(exothermic)(exothermic) Enthalpy change when one mole of water is Enthalpy change when one mole of water is formed from a reaction of an formed from a reaction of an acid with a baseacid with a base ∆
∆ HHccof graphite is the same asof graphite is the same as∆∆ HHf f of COof CO22 C(s, graphite) + OC(s, graphite) + O22(g)(g)COCO22(g)(g) ∆∆ HHθθ==−−393kJmol393kJmol –1 –1
C(s, diamond) + O
C(s, diamond) + O22(g)(g)COCO22(g)(g) ∆∆ HHθθ==−−395kJmol395kJmol –1 –1 ∆∆ HHccof diamond but notof diamond but not∆∆ HHf f of COof CO22sincesince carbon is not in carbon is not in its standardits standard
state state
Graphite is the standard
Graphite is the standard state for carbon(it’s more state for carbon(it’s more thermodynamithermodynamically stable at 298K)cally stable at 298K) 2Li(s) + ½O
2Li(s) + ½O22(g)(g)LiLi22O(s)O(s) ∆∆ HHf f of Liof Li22O is not theO is not the∆∆ HHccof lithium since 2 moles of of lithium since 2 moles of lithium are involved in the equationlithium are involved in the equation
Enthalpy of fusion of H
Enthalpy of fusion of H22OO ∆∆ H for the process HH for the process H22O(s)O(s) HH22O(l)O(l)
Enthalpy of vapourisation of H
Enthalpy of vapourisation of H22OO ∆∆ H for the process HH for the process H22O(l)O(l) HH22O(g)O(g)
1°C ≡
1°C ≡ 1K 1K Heat transfer(J) = m(g) x c xHeat transfer(J) = m(g) x c x TT Specific heat capacity (c)
Specific heat capacity (c)(Jg(Jg –1 –1°C°C –1 –1) Amount of heat required to raise the temperature of 1g of substance by 1K ) Amount of heat required to raise the temperature of 1g of substance by 1K
Temperature
Temperature Measurement of KE of particles(independent of the amount)Measurement of KE of particles(independent of the amount) Heat
Heat Measurement of total energy in a substance(dependent on the Measurement of total energy in a substance(dependent on the amount)amount) Calorimetry
Calorimetry Measurement of heat transferred to known mass of Measurement of heat transferred to known mass of another substance and measuring temp riseanother substance and measuring temp rise Calorimeter
Calorimeter Apparatus used to measure heat given off Apparatus used to measure heat given off in a chemical reactionin a chemical reaction Why
Why∆∆ T may not be accuratT may not be accurate: • e: • Loss of substance(Loss of substance(ethanol) by evaporationethanol) by evaporation •
• Heat transferred to calorimeter/loHeat transferred to calorimeter/lost to surroundings instead of st to surroundings instead of the water(avoided by calibrating apparatus appropriatethe water(avoided by calibrating apparatus appropriately)ly) •
• Incomplete comIncomplete combustion due to inbustion due to inadequate supply oadequate supply of Of O22leading to CO or C(indicated by deposit of leading to CO or C(indicated by deposit of soot on the bottom of soot on the bottom of calorimeter)calorimeter)
1
1ststlaw of thermodynamicslaw of thermodynamics Energy can’t be created or destroyed, only converted from one Energy can’t be created or destroyed, only converted from one form to another form to another
Hess’s law
Hess’s law ∆∆ H for a reaction is H for a reaction is independent of the route it takes independent of the route it takes provided that the temperatures, pressures and physical states of theprovided that the temperatures, pressures and physical states of the reactants and products are the same
reactants and products are the same −
−
− Hess’s law allows for calculation of enthalpy changes for reactions which can’t be Hess’s law allows for calculation of enthalpy changes for reactions which can’t be measured experimentallmeasured experimentally, if statements weren’t truey, if statements weren’t true it’d be possible to create
•
• 150g 23°C 150g 23°C water in water in a glass a glass beaker and beaker and stirred stirred • • After cAfter certain timertain time final e final temp notedtemp noted •
• Spirit Spirit burner burner reweighed reweighed •• ∆∆ m of spirit burner gives mass m of spirit burner gives mass of ethanol burned (0.9g)of ethanol burned (0.9g) •
• Heat gained by Heat gained by water in calowater in calorimeter = mxcxrimeter = mxcx∆∆ T = 150g x 4.2JgT = 150g x 4.2Jg –1 –1°C°C –1 –1x 20°C = 12600Jx 20°C = 12600J
•
• Heat produced by Heat produced by burning 0.9g of eburning 0.9g of ethanol = 12.6kJthanol = 12.6kJ • Mr(C
• Mr(C22HH55OH) = 46gmolOH) = 46gmol –1 –1Ethanol used = 0.9g/46gmolEthanol used = 0.9g/46gmol –1 –1= 0.01956mols= 0.01956mols
•
• So heat produced by burniSo heat produced by burning 1 mol of ethanol = 12.6 x 1/0.01956 = 644kJng 1 mol of ethanol = 12.6 x 1/0.01956 = 644kJ •• ∆∆ HHcc==−−640kJmol640kJmol –1 –1
•
• Note Note temp, temp, 50cm50cm331moldm1moldm –3 –3HCl in insulated polystyrene cup(beaker from HCl in insulated polystyrene cup(beaker from expanded polystyrene)expanded polystyrene)
•
• Add Add 50cm50cm331.1moldm1.1moldm –3 –3 NaOH(exceNaOH(excess to ss to ensure complete reaction)which is at ensure complete reaction)which is at same tempsame temp
•
• Stir continuoStir continuously and note musly and note max temp reacheax temp reachedd HCl(aq) + NaOH(aq)
HCl(aq) + NaOH(aq)NaCl(aq) + HNaCl(aq) + H22O(l)O(l)
Assuming no heat losses to surroundings and
Assuming no heat losses to surroundings and c of solution is c of solution is 4.2Jg4.2Jg –1 –1°C°C –1 –1
Heat absorbed by solution = m x c x
Heat absorbed by solution = m x c x∆∆ T = 100g x 4.2JgT = 100g x 4.2Jg –1 –1°C°C –1 –1x 6.5°C = 2730Jx 6.5°C = 2730J
Acid
Acid= 0.05m= 0.05mol,ol, Heat gHeat given by 1 miven by 1 mol of aciol of acid = 2730J/d = 2730J/0.05m0.05mol = 54.ol = 54.6kJmo6kJmoll –1 –1 ∆∆ HH N
N==−−55kJmol55kJmol –1 –1
−
− Heat loss to surroundings increases with slower reactions asHeat loss to surroundings increases with slower reactions as heat lost over a
heat lost over a longer periodlonger period −
− The greater the heat loss to The greater the heat loss to the surroundings the greater thethe surroundings the greater the correction of the temperature and the steeper the
correction of the temperature and the steeper the lineline •
• 11ststreagent placed in polystyrene cup, temperature noted at 1minreagent placed in polystyrene cup, temperature noted at 1min
intervals for 4min stirring continuously intervals for 4min stirring continuously •
• 22ndndreagent added, temperature noted more reagent added, temperature noted more frequently until maxfrequently until max
reached reached •
• As solution starts tAs solution starts to cool, temperature reco cool, temperature recording and stirringording and stirring continued for 5min
continued for 5min
•
• Check that Check that sign of sign of ∆∆ H is correctH is correct •
• If equation is If equation is multiplied, amultiplied, also multiplylso multiply∆∆ H valueH value •• ∆∆ HHf f of elements is 0of elements is 0
Conversion of graphite to requires high Conversion of graphite to requires high
temperatures and pressures as huge amount of temperatures and pressures as huge amount of energy is needed to disrupt bonds before
energy is needed to disrupt bonds before atoms canatoms can be rearranged into the
be rearranged into the diamond structure(witdiamond structure(withh release of all but 2kJmol
release of all but 2kJmol –1 –1of the energy put in)of the energy put in)
(1)Calculate
(1)Calculate∆∆ H for NH for N22OO44(g)(g)2NO2NO22(g)(g)
2NO
2NO22(g)(g)2NO(g) + O2NO(g) + O22(g)(g) ∆∆ HHθθ==+109+109kJmolkJmol –1 –1
½N
½N22(g) + ½O(g) + ½O22(g)(g)NO(g)NO(g) ∆∆ HHθθ==+90+90kJmolkJmol –1 –1
N N22(g) + 2O(g) + 2O22(g)(g)NN22OO44(g)(g) ∆∆ HHθθ==++8kJmol8kJmol –1 –1 (1) (1) H = [sum of H = [sum of HHθθ f
f products]products] [sum of [sum of HHθθf f reactants]reactants] (2)∆
(2)∆ HHθθ
cc(NH(NH33)?)? ∆∆ HHθθf f NH NH33(g)=(g)= −46.1−46.1kJmolkJmol –1 –1 ∆∆ HHθθf f HH22O(g)=O(g)=−242−242kJmolkJmol –1 –1 (2) (2)4NH4NH33(g) + 3O(g) + 3O22(g)(g)2N2N22(g) + 6H(g) + 6H22O(g)O(g) {6x( {6x(−−242) + 2x0}242) + 2x0}− {4− {4xx(−46) + 3(−46) + 3x0x0} =} =−−1268kJmol1268kJmol –1 –1 ∆ ∆ HHθθ cc(NH(NH33) =) =−−1268/4 = -317 kJmol1268/4 = -317 kJmol –1 –1 (1)(a)Find
(1)(a)Find∆∆ HHf f θθ(CO)using a Hess’s law (CO)using a Hess’s law cycle, cycle, C(graphite) + ½OC(graphite) + ½O22(g)(g)→→CO(g)CO(g)
∆
∆ H H ccθθ(C(graphite)(C(graphite))= )= –394 k–394 kJmolJmol –1 –1 ∆∆ H
H ccθθ(CO(g))= –283 (CO(g))= –283 kJmolkJmol –1 –1
(a) (a) ee .. g . g . C C + + O O C O C O (( H ∆∆H C OC O )) ( ( H ∆∆ H C a rC a r b ob o n )n ) (( H ∆∆H C a rC a r b o n b o n mm o n oo n o x ix i d ed e )) CC OO c o c o m bm b c o c o m bm b f o r m f o r m 22 22 22 11// (( 11 )) ==−−394394−−((−−283) =283) =−−111kJmol111kJmol –1 –1 (b)Suggest why it’s not possible to find
(b)Suggest why it’s not possible to find∆∆ HHf f ((CCOO) ) ddiirreeccttllyy ((bb))((ssoommee))CCOO22 is always produced in the reactionis always produced in the reaction
Enthalpy of dissociation
Enthalpy of dissociation Enthalpy change when 1 mole of a gaseous substance is broken up into free gaseous atomsEnthalpy change when 1 mole of a gaseous substance is broken up into free gaseous atoms (measure of strength of covalent bonds)
(measure of strength of covalent bonds) −
− Bond breaking is endothermic, need energy to break bondsBond breaking is endothermic, need energy to break bonds Bond forming is exothermic, energBond forming is exothermic, energy released when bonds are formedy released when bonds are formed −
− Average Average bond bond enthalpy enthalpy CHCH44(g)(g)C(g) + 4H(g)C(g) + 4H(g) ∆∆ HH θθ= +1664kJmol= +1664kJmol –1 –1 1664/4 = 416kJmol1664/4 = 416kJmol –1 –1
(specific bond enthalpies for the 4C
H = [sum of average bond enthalpies
H = [sum of average bond enthalpies of reactants]of reactants] [ sum of average bond enthalpies of products][ sum of average bond enthalpies of products]
(1)Calculate
(1)Calculate∆∆ HHf f (H(H22O) O) HH22(g) + ½O(g) + ½O22(g)(g)HH22O(l) E(HO(l) E(H−−H)(g) = 436kJmolH)(g) = 436kJmol –1 –1; ; EE((OO==OO))((g) g) = 4= 49988kkJJmmooll –1 –1; ; E(OE(O−−H)(g) = 464kJmolH)(g) = 464kJmol –1 –1
(a)
(a)∆∆ H = [E(HH = [E(H−−H) + ½E(O=O)]H) + ½E(O=O)]−−[2E(O[2E(O−−H)] = [436 + 249]H)] = [436 + 249]−− 928 =928 =−243−243kJmolkJmol –1 –1
∆
∆ H for HH for H22O(g)O(g) HH22O(l);O(l); ∆∆ H =H =−44−44kJmolkJmol –1 –1; ; −−243 + (243 + (−−44) =44) =−−287kJmol287kJmol –1 –1
(b)Suggest why the value obtained in (a)may not be
(b)Suggest why the value obtained in (a)may not be accurate (b)Average values used in bond enthalpiesaccurate (b)Average values used in bond enthalpies (2)When hydrogen reacts with chlorine in a container of fixed
(2)When hydrogen reacts with chlorine in a container of fixed volume the pressure increases but the number of volume the pressure increases but the number of molecules has notmolecules has not changed.
changed. What is What is the sign of the sign of ∆∆ H?H? (2)H
(2)H22(g) + Cl(g) + Cl22(g)(g)2HCl(g) As the number of molecules doesn’t change during 2HCl(g) As the number of molecules doesn’t change during the reaction, the only reason for an the reaction, the only reason for an increase in pressureincrease in pressure
can be an increase in temper
can be an increase in temperature. ature. This means that the reaThis means that the reaction is exothermic andction is exothermic and∆∆ H is negativeH is negative (3)Is
(3)Is∆∆ HHcc(H(H22) same as) same as∆∆ HHf f (H(H22O)? O)? (3)Yes, (3)Yes, provided provided the the conditions conditions are are the the same same HH22(g) + ½O(g) + ½O22(g)(g)HH22O(l)O(l)
(4)Is
(4)Is∆∆ HHcc(CO) the same as(CO) the same as ∆∆ HHf f (CO(CO22)?)? (4)Ent(4)Enthalhalpy cpy chanhanges ages are nore not tht the sae same eme even tven thouhough tgh they hey botboth proh producduce 1 moe 1 mole of le of COCO22
(5)Define
(5)Define∆∆ HHf f θθ(urea) (urea) (5) • Enthalpy change for the formation of 1 mol of urea, from its elements, in their standard states(5) • Enthalpy change for the formation of 1 mol of urea, from its elements, in their standard states/100kPa 298K /100kPa 298K
(6)(a) Find
(6)(a) Find∆∆ H H for: for: 2C(graphite) 2C(graphite) + + 2H2H22(g) + O(g) + O22(g)(g)→→CHCH33COOH(l)COOH(l) ∆
∆ HHcc(C(graphite)(C(graphite))= )= –394kJmol–394kJmol –1 –1 ∆∆ H
Hcc(H(H22(g))= –286kJmol(g))= –286kJmol –1 –1 ∆∆ H
Hcc(CH(CH33COOH(l))COOH(l))= = –874kJmol–874kJmol –1 –1
(a)
(a)∆∆ H H = [2(= [2(∆∆ H H cc(C)) + 2((C)) + 2(∆∆ H H cc(H(H22))]))]−−[[∆∆ H cc(CH H (CH33COOH)] =COOH)] =−−486 kJ mol486 kJ mol –1 –1 (b)What is the(b)What is the ∆∆ H obtained in (a) called? (b)H obtained in (a) called? (b) ∆∆ HHf f
33 00 22 99 22 88 22 77 22 66 22 55 22 44 22 33 22 22 22 11 22 00 00 44 88 11 22 11 66 22 00 22 44 22 88 33 22 33 66 44 00 V o l V o l u mu m e o f N a Oe o f N a O HH (( a q ) / a q ) / c mc m T e m T e m p e r a tp e r a t u r e / ºu r e / º CC – – 33 (7)(a) 20cm
(7)(a) 20cm33 1moldm1moldm –3 –3copper salt(aq) in a polycopper salt(aq) in a polystyrene cup. styrene cup. Burette fillBurette filled with 2moldmed with 2moldm –3 –3 NaOH(aq)NaOH(aq) 2cm
2cm33 NaOH(aq) was run into the copper salt(aq) and temp measureNaOH(aq) was run into the copper salt(aq) and temp measured immediately. d immediately. As soon as possible a further 2cmAs soon as possible a further 2cm33 of NaOH(aq)of NaOH(aq) was run in and
was run in and temp measured again, process continued until 36cmtemp measured again, process continued until 36cm33 of NaOH(aq) had been addedof NaOH(aq) had been added (i)Explain why the temp reaches a max and
(i)Explain why the temp reaches a max and then falls slightly on addition of further NaOH(aq)then falls slightly on addition of further NaOH(aq) (i)Reaction is complete, addition of cooler NaOH causes temp to fall
(i)Reaction is complete, addition of cooler NaOH causes temp to fall (ii)Calculat
(ii)Calculate e the the amount amount of of copper copper ions ions that that have have reacted reacted (ii)20(ii)20××1/1000 =0.02mol1/1000 =0.02mol (iii)Wr
(iii)Write ite the the formula formula of of the the copper copper hydroxide hydroxide that that is is produced produced (iii)Cu(OH(iii)Cu(OH))22 (b)Identify a source of error in this experiment, and
(b)Identify a source of error in this experiment, and say what you would do to say what you would do to reduce its effectreduce its effect (b) •
(b) • Poor mixing, use(magnetPoor mixing, use(magnetic stirrer/swirl cup)beic stirrer/swirl cup)between additions, totween additions, to ensure even temp/reaction faster so less heat loss with timeensure even temp/reaction faster so less heat loss with time •
• Solutions at differeSolutions at different initial temperatures, allow them to stabint initial temperatures, allow them to stabilise at RTlise at RT •
• Measure temMeasure temperature more perature more often. often. Allows foAllows for more acr more accuratecurate∆∆ ΤΤ from graphfrom graph (8)A student calculates
(8)A student calculates∆∆ HHccθθ (C(C22HH55OH) = 853.54966 kJ molOH) = 853.54966 kJ mol –1 –1 Give 3 criticisms of the value giving Give 3 criticisms of the value giving reasonsreasons (8) •
(8) • Shown as standard valuShown as standard value. Experiment not conduce. Experiment not conducted under ‘standard’ conditited under ‘standard’ conditionsons •
Organic chemistry
Organic chemistry The study of the chemistry of carbon compoundsThe study of the chemistry of carbon compounds Homologous series
Homologous series A set of comA set of compounds with • pounds with • similar chesimilar chemical propertiemical properties • s • same functional same functional groups • groups • a general forma general formula whereula where successive members differ by CH
successive members differ by CH22
Structural formula
Structural formula How the various atoms are bonded How the various atoms are bonded to one another within the to one another within the moleculemolecule -
- Factors Factors affecting affecting reactivity reactivity in in organic organic compounds compounds • • single single or or double double bonds bonds • • bond bond polarity polarity • • bond bond enthalpyenthalpy -
- Larger alkanes releLarger alkanes release a lot more energy per mole bease a lot more energy per mole because they have more bonds to reacause they have more bonds to reactct -
- Carbon can catenate(fCarbon can catenate(form stable covalent bonds wiorm stable covalent bonds with itself)th itself) -
- Organic compounds therOrganic compounds thermodynamically modynamically unstable in the presence of oxygunstable in the presence of oxygenen CHCH44(l) + 2O(l) + 2O22(g)(g) COCO22(g) + 2H(g) + 2H22O(g)O(g) (-)(-)∆∆ HH
But activation energies of the reactions with oxygen are high
But activation energies of the reactions with oxygen are high so organic compounds are kinetically stable at temperatures on earthso organic compounds are kinetically stable at temperatures on earth If alkane and oxygen mixed
If alkane and oxygen mixed first explosion will result on ignitionfirst explosion will result on ignition Carbon Carbon ground state ground state 2 2ss 22pp CCaarrbboonn excited excited state state 2 2ss 22pp -
- If one electron is promoted from the 2s orbital to the 2p orbital, 4 unpaired electrons become availableIf one electron is promoted from the 2s orbital to the 2p orbital, 4 unpaired electrons become available -
- Energy to do this is more than compensated for by the energy released in the formation of 4 bonds instead of 2Energy to do this is more than compensated for by the energy released in the formation of 4 bonds instead of 2 -
- Electrons not all equal since they are in different typeElectrons not all equal since they are in different types of orbital(s & p, methane has 3 bonds of different length from the other one, sos of orbital(s & p, methane has 3 bonds of different length from the other one, so electrons are hybridised)
electrons are hybridised) Isomer
Isomer Same molecular formula, different Same molecular formula, different structural formulaestructural formulae
Structural isomerism
Structural isomerism Occurs when 2 or Occurs when 2 or more different structural formulae can be written for the same molecular formulamore different structural formulae can be written for the same molecular formula Chain isomers
Chain isomers Different arrangements of carbon skeletonDifferent arrangements of carbon skeleton
Similar chemical properties, differ in physical properties(Mt)because of change Similar chemical properties, differ in physical properties(Mt)because of change in shape of molecule
in shape of molecule
Positional isomers
Positional isomers Same skeleton and functional group, Same skeleton and functional group, side chains/functionalside chains/functional groups are in different positions on the
groups are in different positions on the carbon chaincarbon chain Differ in physical
Differ in physical propertiesproperties
Functional group isomers
Functional group isomers Same atoms arranged into different Same atoms arranged into different functional groupsfunctional groups Differ in
Differ in physical & chphysical & chemical propertiemical propertieses
Evidence that the 2 bonds in the C=C double bond are not the same: Evidence that the 2 bonds in the C=C double bond are not the same: •
• Bond enerBond energy of C=C gy of C=C (612kJmol(612kJmol –1 –1) is greater than C-C (348kJmol) is greater than C-C (348kJmol –1 –1) but not as twice as big hence pi bond is weaker than the sigma) but not as twice as big hence pi bond is weaker than the sigma
bond bond
•
• GrGreaeateter sr strtrenengtgth of h of C=C=C bC bonond sd supuppoportrted ed by by shshororteter bor bond nd lelengngthth(h(henence gce grereatater er ovovererlalap)p) • • ExExisistetencnce of e of gegeomometetriric ic isosomemersrs Stereoisomerism
Stereoisomerism Molecules have same molecular formula, same Molecules have same molecular formula, same structuralstructural formula, but atoms have a different 3d
formula, but atoms have a different 3d arrangement(oriarrangement(orientation in space).entation in space). Differ in physical
Differ in physical propertiesproperties
Stereoisomer
Stereoisomerism found in any ism found in any molecule of the type:molecule of the type:
Geometric Isomerism
Geometric Isomerism Occurs when there’s restricted rotation about a bond(C=C double bond where each Occurs when there’s restricted rotation about a bond(C=C double bond where each of the two C atoms of the two C atoms carriescarries 2 different atoms/groups)differ in physical properties(different positions of groups, chains
2 different atoms/groups)differ in physical properties(different positions of groups, chains affects shape, dipoles, intermolecular forces)affects shape, dipoles, intermolecular forces) Single sigma bond
Single sigma bond Free rotation about this bond without any reduction in Free rotation about this bond without any reduction in degree of overlapdegree of overlap Double bond
Double bond Restricted rotation about C=C double bond because rotation would lead to Restricted rotation about C=C double bond because rotation would lead to a decrease in overlap of p a decrease in overlap of p orbitals that give theorbitals that give the pi bond.
Nucleophiles
Nucleophiles Species which seek out + centres. A molecule, atom or ion which can donate a lone pair of electrons to form a new dativeSpecies which seek out + centres. A molecule, atom or ion which can donate a lone pair of electrons to form a new dative covalent bond
covalent bond Electrophiles
Electrophiles Species which seek out – centres. An Species which seek out – centres. An electron deficient molecule, atom or ion, capable of accepting a lone electron deficient molecule, atom or ion, capable of accepting a lone pair of electronspair of electrons to form a new dative covalent bond
to form a new dative covalent bond Aromatic compounds
Aromatic compounds Always contain rings, don’t show the properties expected of compounds with double Always contain rings, don’t show the properties expected of compounds with double bonds(benzene)bonds(benzene) Aliphatic compounds
Aliphatic compounds Don’t contain rings, contain double bonds and show Don’t contain rings, contain double bonds and show the expected reactions eg alkenesthe expected reactions eg alkenes Alkanes
Alkanes CCnnHH2n+22n+2 Simplest homologous series, saturated hydrocarbonsSimplest homologous series, saturated hydrocarbons (every C atom has 4
(every C atom has 4 single bonds with other atoms and it’s single bonds with other atoms and it’s impossible for carbon to make more than impossible for carbon to make more than 4 bonds hence alkanes are 4 bonds hence alkanes are saturated)saturated) n
n FFoorrmmuullaa NNaammee BBt t °°CC MMt t °°CC CCoolloouurrlleesss s ggaasseess
Methane used in homes for
Methane used in homes for cooking, heatingcooking, heating Propane/butane, mobile sources of heat/light Propane/butane, mobile sources of heat/light for camping
for camping 1
1 CHCH44 MMeetthhaannee --116622 --118822
2
2 CC22HH66 EtthEhaannee --8899 --118833
3
3 CC33HH88 PrroP oppaannee --4422 --118888
4
4 CC44HH1010 BuButtaannee --00..55 --113388
5
5 CC55HH1212 PPeennttaannee 3366 --113300 CC55– C– C1515colourless liquids, liquid alkanes used in petrol for carscolourless liquids, liquid alkanes used in petrol for cars
6
6 CC66HH1414 HHeexxaannee 6969 --9955 CC1515+ + white white waxy waxy solidssolids
7
7 CC77HH1616 HeepH pttaannee 9988 --9911 - - MMaaiin n ssoouurrccees s oof f aallkkaannees s ffrroom m ccrruudde e ooiill, , nnaattuurraal l ggaass
-
- Organic materials manufaOrganic materials manufactured from alkanes, detergents, plastictured from alkanes, detergents, plastics, synthetic fibrescs, synthetic fibres -
- Inorganic materials manufaInorganic materials manufactured from alkanes, hydrogen from processectured from alkanes, hydrogen from processed alkanes isd alkanes is used to make ammonia
used to make ammonia 8 8 CC88HH1818 OOccttaannee 112266 --5577 9 9 CC99HH2020 Nonane Nonane 10 10 CC1010HH2222 DecaneDecane
Mt of alkanes depends on size & shape: Mt of alkanes depends on size & shape: •
• Alkanes have covalent bonds within moleculAlkanes have covalent bonds within molecules and intermolecular van der waals forceses and intermolecular van der waals forces •
• A branched chain alkane has a lower Mt than straight chain isomer as branched chain alkanes can’t pack as closely together and haveA branched chain alkane has a lower Mt than straight chain isomer as branched chain alkanes can’t pack as closely together and have smaller molecular surf
smaller molecular surface areas so van der waals forces are reduced. ace areas so van der waals forces are reduced. Therefore Mt decreases as branching increaseTherefore Mt decreases as branching increasess -
- Fractional distFractional distillation of crude oil: illation of crude oil: Separation of mixtuSeparation of mixture of alkanes and hydrocare of alkanes and hydrocarbons into groups of compounds with sirbons into groups of compounds with similar Btsmilar Bts Alkyl groups
Alkyl groups-C-CnnHH2n + 12n + 1 Not capable of independent existence but occurs within other molecules, CH Not capable of independent existence but occurs within other molecules, CH33methyl group, CHmethyl group, CH22CHCH33ethyl groupethyl group
Nomenclature
Nomenclature A A systematic systematic way way of of naming naming chemical chemical compounds compounds - - Names Names based based on on longest longest continuous continuous C C chainchain Alkyl group names come before name of
Alkyl group names come before name of longest C chain preceded, by a longest C chain preceded, by a number to indicate C atom at which number to indicate C atom at which substitution occurredsubstitution occurred Structural Isomerism
Structural Isomerism In alkanes, only way in which different structures can be In alkanes, only way in which different structures can be obtained is by rearranging the C chainobtained is by rearranging the C chain •
• Straight chain isomer C atoms joineStraight chain isomer C atoms joined together in a continuous chain(bending chain doesn’t change length of C chain)d together in a continuous chain(bending chain doesn’t change length of C chain) •
• Branched chain isomeBranched chain isomer r C atoms form ‘side cC atoms form ‘side chains’ which can’t be of greathains’ which can’t be of greater length than main chainer length than main chain 3 struc
3 structural isomer tural isomer of of CC55HH1212 CHCH33CHCH22CHCH22CHCH22CHCH33
Pentane Bt36°C Pentane Bt36°C CH CH33(CH(CH22))33CHCH33 CH CH33 || CH CH33CHCH22CHCHCHCH33 2-methylbutane Bt28°C 2-methylbutane Bt28°C CH CH33CHCH22CH(CHCH(CH33))22 CH CH33
|| 22,,22--ddiimmeetthhyyllpprrooppaanne e BBtt1100°°CC CH CH33CCHCCH33 CHCH33C(CHC(CH33))33 || CH CH33 •
• Alkanes non-polar, not reactiAlkanes non-polar, not reacting with polar chemicals(doesn’t dissolve in waterng with polar chemicals(doesn’t dissolve in water)) •
• Alkanes react witAlkanes react with non-polar substances given eh non-polar substances given enough energynough energy Burning fuels
Burning fuels • • Greenhouse effecGreenhouse effect(Increases greenhout(Increases greenhouse gases(COse gases(CO22))which absorb IR radiation and stop Earth’s IR radiation getting out)))which absorb IR radiation and stop Earth’s IR radiation getting out)
earth warms up slowly, climate changes, polar ice caps melt leading to
earth warms up slowly, climate changes, polar ice caps melt leading to flooding.flooding.
Control global warming by using cars less, replacing fossil fuels with other sources of
Control global warming by using cars less, replacing fossil fuels with other sources of energy (natural energy, wind, water)energy (natural energy, wind, water) •
• Power stations add sulphur oxides to the air(scrPower stations add sulphur oxides to the air(scrubbers reduce emissions)which are poisonous causing problubbers reduce emissions)which are poisonous causing problems for people with asthma,ems for people with asthma, causes acid rain which kills trees, damages buildings, makes lakes acidic killing aquatic life
causes acid rain which kills trees, damages buildings, makes lakes acidic killing aquatic life •
• Incomplete cIncomplete combustion(insuffombustion(insufficient Oicient O22supply)producesupply)produces poisonous gas s poisonous gas CO, vehicle engines make nitrogen oxides which add to CO, vehicle engines make nitrogen oxides which add to acidacid
rain problem, fuel which comes out without burning (unburned hydrocarbons) escape into the
rain problem, fuel which comes out without burning (unburned hydrocarbons) escape into the air as pollutantsair as pollutants Renewable biofuels
Renewable biofuels From plants, produce COFrom plants, produce CO22when burned but plants take in COwhen burned but plants take in CO22so if replaced, won’t add to COso if replaced, won’t add to CO22in the atmosphere.in the atmosphere.
•
• Biodiesel made frBiodiesel made from rapeseed oil, used in vehicom rapeseed oil, used in vehicles • les • Ethanol made by feEthanol made by fermenting sugar cane, mixrmenting sugar cane, mixed with petrol, fuel used in veed with petrol, fuel used in vehicleshicles Cyclic alkanes
Cyclic alkanes Bond angles for smaller rings are different from 109° Bond angles for smaller rings are different from 109° of the spof the sp33
hybrid orbitals indicating poor overlap of the orbitals and considerable strain on hybrid orbitals indicating poor overlap of the orbitals and considerable strain on the ring.
the ring. -
- They behave as normal aThey behave as normal alkanes concerning the C-H bond but alkanes concerning the C-H bond but are more reactivere more reactive towards reagents which break the C-C bond
towards reagents which break the C-C bond
CH CH22 CHCH22– CH– CH22 CHCH22 / / \ \ | | | | / / \\ CH CH22– CH– CH22 CHCH22– CH– CH22 CHCH22 CHCH22 Cyclopropane
Cyclopropane Cyclobutane Cyclobutane | | || CH CH22 CHCH22 \ \ // CH CH22 Cyclohexane Cyclohexane
Halogenation
Halogenation Halogen atom replaces 1 or more of the H atoms in an alkane by aHalogen atom replaces 1 or more of the H atoms in an alkane by a substitution reactionsubstitution reaction(atom/group of atoms in a(atom/group of atoms in a molecule replaced by another atom/group of atoms)
molecule replaced by another atom/group of atoms) -
- ALL halogens react with ALL alkaALL halogens react with ALL alkanes, rate of reaction quicker with Cl than with Br than with I, I reaction results in equilibriunes, rate of reaction quicker with Cl than with Br than with I, I reaction results in equilibriumm -
- Rate of reaction decrRate of reaction decreases as the relative moleeases as the relative molecular mass of the alkane increcular mass of the alkane increasesases Free radical substitution reaction
Free radical substitution reaction substitution involving a free radical(species which have a single unpaired electron, highlysubstitution involving a free radical(species which have a single unpaired electron, highly reactive)
reactive)
Photochemical reaction
Photochemical reaction Reaction initiated by light, Sunlight(UV)light energy essential for reactions to proceed Reaction initiated by light, Sunlight(UV)light energy essential for reactions to proceed at a at a reasonable ratereasonable rate UV
UV C
C66HH1414+ Br+ Br22 CC66HH1313Br + HBrBr + HBr(steamy acidic fumes)(steamy acidic fumes)
Rapid decolourisation of bromine, if covered in a
Rapid decolourisation of bromine, if covered in a darkened test tube the colour remains longer darkened test tube the colour remains longer -
- All C-H bonds equivalent so no way of determining which H atom will be replaceAll C-H bonds equivalent so no way of determining which H atom will be replacedd Initiation reactions
Initiation reactions Free radicals producedFree radicals produced Photo dissociationPhoto dissociationClCl222Cl•2Cl•
Homolytic bond fission
Homolytic bond fission (C(Covaovalenlent)bt)bond ond splsplits its equequallally ty to gio give 2 ve 2 frefree rae radicdicalsals XX::YYX• + Y•X• + Y• Heterolytic bond fission
Heterolytic bond fission Bond splits unequally and both electrons kept by Bond splits unequally and both electrons kept by one atomone atom Bond fission
Bond fission Bond breakingBond breaking Lysis Lysis BreakdownBreakdown Homo Homo SameSame Hetero Hetero DifferentDifferent Heterolytic
Heterolytic Bond cleavage where + & – ions producedBond cleavage where + & – ions produced Homolytic Homolytic Bond cleavage where 2 neutral species producedBond cleavage where 2 neutral species produced Propagation reactions
Propagation reactions Free radicals used up and Free radicals used up and created in chain reactioncreated in chain reaction Cl• + CH
Cl• + CH44CHCH33• + • + HCl HCl CHCH33• + Cl• + Cl22CHCH33Cl Cl + + Cl• Cl• etc etc until until no no more more ClCl22/ CH/ CH44moleculesmolecules
Termination reactions
Termination reactions Free radicals mopped upFree radicals mopped up 2 free radicals join together making a
2 free radicals join together making a stable molecule, some products forming trace impurities in final samplestable molecule, some products forming trace impurities in final sample L
Lotots os of f popossssiiblble te terermmininaatitioon rn reeacactitioonsns CCl• l• + C+ Cl•l•ClCl22 or or Cl• Cl• + + CHCH33••CHCH33CCll oor r CCHH33• + CH• + CH33••CHCH33Cl + CCl + C22HH66
More substitutions
More substitutions Dependent on amount of excess chlorine or Dependent on amount of excess chlorine or methanemethane Exce
Excess chloriss chlorinene Cl• free radCl• free radicalicals start attacs start attacking chlorking chloromethomethane givinane giving dichlorg dichloromethomethane CHane CH22ClCl22trichloromethane trichloromethane CHClCHCl33
tetrachloromet
tetrachloromethane hane CClCCl44
Exce
Excess methss methaneane ProdProduct wiuct will be mosll be mostly ctly chlorhloromethomethaneane Alkenes
Alkenes CCnnHH2n2n Unsaturated molecules because of C=C double bondUnsaturated molecules because of C=C double bond -
- Alkenes have lower Mt because less H atoms, so lower van der waals forces but more reactive because of C=C double bondAlkenes have lower Mt because less H atoms, so lower van der waals forces but more reactive because of C=C double bond Structural Isomerism
Structural Isomerism Occurs by moving the double bond Occurs by moving the double bond to different positions in the C chain to different positions in the C chain indicated by the number between theindicated by the number between the prefix & -ene, number being the smallest
prefix & -ene, number being the smallest possible counting from each end which takes precedence in numbering of the C atoms of thepossible counting from each end which takes precedence in numbering of the C atoms of the longest C chain(isomer 3-methylbut-1-ene is
longest C chain(isomer 3-methylbut-1-ene is not 2-methylbut-3-ene)not 2-methylbut-3-ene) -
- 3 possibil3 possibilities of ities of CC44HH88 but-1-ene CHbut-1-ene CH33CHCH22CH=CHCH=CH22 (-cis or (-cis or -trans)but-2-ene-trans)but-2-eneCHCH33CH=CHCHCH=CHCH33
Addition reaction
Addition reaction 2 molecules react together forming a single product2 molecules react together forming a single product Electrophilic addition
Electrophilic additionAddition reaction where, electrophile attacks a molecule at a region of highAddition reaction where, electrophile attacks a molecule at a region of high electron density
electron density -
- Electophilic additioElectophilic addition reaction of alkenes at high electron density(pi bond, double bond is nucleophilic)n reaction of alkenes at high electron density(pi bond, double bond is nucleophilic) pi bond breaks, bonds formed with
pi bond breaks, bonds formed with reactant moleculereactant molecule
H H HH HH HH | | | | RRT T | | || –C –C=C=C–– + A+ A–B–B –C–C– –C–C– | | || A A BB Tests for unsaturation C=C bond
Tests for unsaturation C=C bond
Pure bromine a safety hazard, avoided by dissolving it in
Pure bromine a safety hazard, avoided by dissolving it in an organic solvent(hexane)an organic solvent(hexane) RT, shake(as hydrocarbons are immiscible with water) RT, shake(as hydrocarbons are immiscible with water) CH
CH33CH=CHCHCH=CHCH33++BrBr2(aq)2(aq) CHCH33CHBrCHBrCHCHBrCHBrCH33decolouriseddecolourised B
Buutt--22--eenne e 22,,33--ddiibbrroommoobbuuttaannee((ddiibbrroommooaallkkaanne)e) CH
CH22=CH=CH22+ + HH22O + [O]O + [O] HOCHHOCH22CHCH22OHOH [O][O]oxygen from the oxidising agentoxygen from the oxidising agent
E
Etthheenne e eetthhaannee--11,,22--ddiiooll Oxidation of alkenes by
Oxidation of alkenes by purple purplealkalinealkalineKMnOKMnO44(potassium (potassium manganate(VIImanganate(VII)))) (warning, other reducing agents give (warning, other reducing agents give positive results)positive results) •• CHCH22=CH=CH22++2MnO2MnO44 – – + 2OH+ 2OH – – HOCHHOCH22CHCH22OH +OH +2MnO2MnO442– 2–
Manganate ions
Manganate ionsfirst reduced tofirst reduced to green manganate ions, green solutiongreen manganate ions, green solution
•• 3CH3CH22=CH=CH22++2MnO2MnO44 – – + 4H+ 4H2O2O HOCHHOCH22CHCH22OH +OH +2MnO2MnO22+ 2OH+ 2OH – –
((neutral or acidicneutral or acidic conditions, no OHconditions, no OH – – /H/H++on on LLHHSS)) tthheen n ttoo dark brown ppt manganese dioxidedark brown ppt manganese dioxide
Oxidation of alkenes by
Oxidation of alkenes by acidicacidicpurple KMnOpurple KMnO44turnsturns colourlesscolourless, manganate(VII) ions reduced to manganese(II) ions, manganate(VII) ions reduced to manganese(II) ions 5CH
Alkene with H
Alkene with H22 Addition, reduction reactionAddition, reduction reaction
-
- Cheaper nickel catalCheaper nickel catalyst used to convert unsaturyst used to convert unsaturated oils into saturateated oils into saturatedd fats for use in
fats for use in margarinemargarine
Finely divided
Finely divided nickel/platinum catalystnickel/platinum catalyst H
H HH 150°C150°C H H HH \
\ // High PressureHigh Pressure | | || C C==CC ++ HH22(g)(g) H–C–C–HH–C–C–H / / \ \ | | || H H HH HH HH Ethene(
Ethene(AlkeneAlkene)) EEtthhaannee((AlkaneAlkane)) Alkene with HBr
Alkene with HBr RTRTElectrophilic additionElectrophilic addition H
H22C=CHC=CH22+ HBr(not aq)+ HBr(not aq) CHCH33CHCH22BrBr
E
Etthhaanne e BBrroommooeetthhaannee((BBrroommooaallkkaanne e ccoolloouurrlleesss s lliiqquuiidd)) H
H22C=CHCHC=CHCH22CHCH33+ HBr+ HBr 2 products2 products BrCHBrCH22CHCH22CHCH22CHCH33 1-bromobutane1-bromobutane
CH
CH33CHBrCHCHBrCH22CHCH33 2-bromobutane2-bromobutane
Major product because more stable with more attached alkyl groups Major product because more stable with more attached alkyl groups Alkenes with H
Alkenes with H22SOSO44(catalyst)(catalyst) Electrophilic addition,Electrophilic addition,hydrolysishydrolysis cold conc Hcold conc H22SOSO44 H
H22C=CHC=CH22 CHCH33CHCH22OHOH
Alkene with H
Alkene with H22O(g)O(g) Reaction yield low 5%, recycle unreacted gas to get yield 95%Reaction yield low 5%, recycle unreacted gas to get yield 95%
300°C 60atm H
300°C 60atm H33POPO44(s)(s)Phosphoric(V) acid catalystPhosphoric(V) acid catalyst
H
H2C=CH2C=CH22(g) + H(g) + H22O(g) O(g) CHCH33CHCH22OH(g)OH(g)
Poly(eth
Poly(ethe e ne)‘polne)‘polythene’ythene’
Addition polymerisation, electrophilic addition reaction Addition polymerisation, electrophilic addition reaction (H
(H22C=CHC=CH22))nn (–CH(–CH22 –CH –CH22 –) –)nn
Monomer ethene(repeating unit, essentially an alkane) Monomer ethene(repeating unit, essentially an alkane) Ziegler Natta catalysts are mixtures of
Ziegler Natta catalysts are mixtures of titaniumtitanium compounds like titanium(III)chloride TiCl compounds like titanium(III)chloride TiCl 33or or
titanium(IV)
titanium(IV)chloride chloride TiCl TiCl 44and compounds of and compounds of
aluminium like aluminium triethyl Al(C aluminium like aluminium triethyl Al(C 22 H H 55 ) )33
LDPE(Low D
LDPE(Low Density Polytheneensity Polythene) ) Polymer chains very brancPolymer chains very branched, not packinghed, not packing closely, amorphous(non
closely, amorphous(non crystallinecrystalline)) • Strong • Flexible • Deformed by heat • Strong • Flexible • Deformed by heat -
- Used in bags, bottles, paUsed in bags, bottles, packaging, electrical inckaging, electrical insulationsulation -
- LDPE LDPE made made by by ethene ethene atat 2000atm 500K 2000atm 500K HDPE(Hig
HDPE(High Density Polytheneh Density Polythene) ) Polymer chains brancPolymer chains branched little, chains line uphed little, chains line up packing closely,
packing closely, crystalline structurecrystalline structure
• Strong • Rigid • Not deformed by heat • Easy to mould • Strong • Rigid • Not deformed by heat • Easy to mould -
- Used in water pipes, petrUsed in water pipes, petrol tanks, containers, hospol tanks, containers, hospital equipment needingital equipment needing sterilising
sterilising -
- HDPE maHDPE made by ethede by ethene atne at 25atm 330K Ziegler Natta catalyst25atm 330K Ziegler Natta catalyst Poly(propene)
Poly(propene) H
H CHCH33 Ziegler NattaZiegler Natta HH CHCH33 | | || || || ( C=C ) ( C=C )nn ( –C–C– )( –C–C– )nn | | || || || H H HH HH HH -
- PolymerisPolymerisation of propene produces stereoregular polymeration of propene produces stereoregular polymers, regular geometricals, regular geometrical arrangement of methyl groups in a spiral which stiffens the structure allowing the long arrangement of methyl groups in a spiral which stiffens the structure allowing the long molecules to line up close to
molecules to line up close to one another, increasingone another, increasing • H
• Hardness ardness • • Wear-resistanWear-resistance, stce, strength rength of thof the mae material terial • • Softening Softening temptemp -
- Longer chains means greater van der waals forces which get tangled so less flexibilLonger chains means greater van der waals forces which get tangled so less flexibilityity -
- Used to make ropes, sackiUsed to make ropes, sacking, carpets, fishing netng, carpets, fishing netss
Poly(chloroethene) PVC Poly(chloroethene) PVC -
- Amorphous, large chlorines sticAmorphous, large chlorines stick out randomly from the chains so they don’t pack closelyk out randomly from the chains so they don’t pack closely -
- PVC unusually hard & rigid because C–Cl bonds are polarisPVC unusually hard & rigid because C–Cl bonds are polarised(Cl more EN than C)dipole-dipoleed(Cl more EN than C)dipole-dipole in
inttereracactitionons es exixisst bt betetwweeeen cn chahaininss TTo mo makake Pe PVVC mC morore fe flelexixiblble, e, plplaaststiiciciseserrs as are re adaddededd To make PVC more hard, mineral fillers are added To make PVC more hard, mineral fillers are added -
- Used for water pipes(rigidityUsed for water pipes(rigidity, resistance to wear), rainwear, resistance to wear), rainwear, coating on electric cables(at high temps can, coating on electric cables(at high temps can melt causing short circuits and give toxic chlorine containing compounds)
melt causing short circuits and give toxic chlorine containing compounds)
H H CCl l H H CCll | | | | | | || ( C=C ) ( C=C )nn ( –C–C– )( –C–C– )nn | | | | | | || H H HH HH HH Chloroethene PVC Chloroethene PVC Poly(fluoroethene)PTFE or Teflon
Poly(fluoroethene)PTFE or Teflon - Solid - Solid is is • • Hard, Hard, strong strong • • Slippery Slippery • • High High MtMt -
- PTFE PTFE inert becainert because • use • C–F bond C–F bond is stronis strong • g • Resistant Resistant to hydrolto hydrolysisysis •
• Big F atoms proteBig F atoms protect C chain from chemicact C chain from chemical attack l attack -
- PTFE has high elecPTFE has high electron density due to F atotron density due to F atoms and close packing,ms and close packing, Vdw forces stronger than HDPE
Vdw forces stronger than HDPE -
- Used in surface coating for non-stick ovenware, low fricUsed in surface coating for non-stick ovenware, low friction bearings, seals, pipes, skis,tion bearings, seals, pipes, skis, stain–proofing of fabrics stain–proofing of fabrics F F FF FF FF | | | | | | || ( C=C ) ( C=C )nn ( –C–C– )( –C–C– )nn | | | | | | || F F FF FF FF Tetr
Tetrafluafluroetroethenehene PolyPoly(tet(tetraflrafluroeuroethenethene)) -
- Polymers cause environmPolymers cause environmental problems when disposed, when burned, give off toxic fumes, not biodegradaental problems when disposed, when burned, give off toxic fumes, not biodegradable so would accumulate inble so would accumulate in rubbish tips never to disappear
rubbish tips never to disappear -
- Polymers can be recyclePolymers can be recycled(but expensive to sort out plastics)break waste polymerd(but expensive to sort out plastics)break waste polymers into smaller molecules by cracking, use the smalls into smaller molecules by cracking, use the small molecules as raw materials for making new polymers or other chemicals
Ideal fuel should
Ideal fuel should1 1 Be Be abundant abundant Methane, butane, octane, coal, finitMethane, butane, octane, coal, finite resources. e resources. Ethanol replaceaEthanol replaceable by fermentation of sugars of ble by fermentation of sugars of vegetable origin, however if earth’s energy needs were to be
vegetable origin, however if earth’s energy needs were to be met by ethanol it is debatable whether enough met by ethanol it is debatable whether enough vegetable matter could bevegetable matter could be produced.
produced.
Hydrogen obtained by electrolysis of water, burning it converts it back to
Hydrogen obtained by electrolysis of water, burning it converts it back to its source, regenerated by electrolysis where oxygen used toits source, regenerated by electrolysis where oxygen used to burn it is recovered.
burn it is recovered. But fuel required to produce energy, and more than all the energy is used to recover the fuelBut fuel required to produce energy, and more than all the energy is used to recover the fuel 2
2 Be easy & safBe easy & safe to store & me to store & moveove (high E(high EACTACTfor combustion reacfor combustion reaction) tion) Transport of liquid fueTransport of liquid fuel is dangerous but gases more so.l is dangerous but gases more so.
-
- Liquid fuels are easy to store/transLiquid fuels are easy to store/transport whereas gases will need to be stored under pressure in a special container as a liquid/in a largeport whereas gases will need to be stored under pressure in a special container as a liquid/in a large container as a gas
container as a gas
Hydrogen is difficult, a highly flammable gas, can’t be liquefied under pressure at RT, the
Hydrogen is difficult, a highly flammable gas, can’t be liquefied under pressure at RT, the more stored the higher the pressure, themore stored the higher the pressure, the stronger and heavier the container must be, so
stronger and heavier the container must be, so storage & transport of hydrogen is dangerous due storage & transport of hydrogen is dangerous due to risk of explosionto risk of explosion Liquid oxygen & liquid nitrogen are transported on roads
Liquid oxygen & liquid nitrogen are transported on roads daily, light weight insulated containers safely ‘leak away’ excess pressuredaily, light weight insulated containers safely ‘leak away’ excess pressure 3
3 Be Be non toxnon toxicic Hydrogen & methane can be breathed in, Hydrogen & methane can be breathed in, in small amounts without harmin small amounts without harm Butane, octane have narcotic and hallucinogenic properties in small amounts, and poisonous in
Butane, octane have narcotic and hallucinogenic properties in small amounts, and poisonous in larger quantitieslarger quantities Ethanol poisonous in small amounts, taken continuously causes long term damage to
Ethanol poisonous in small amounts, taken continuously causes long term damage to organs of the bodyorgans of the body 4
4 Have a hiHave a high calorific gh calorific valuevalue (high energy density) (high energy density) Hydrocarbons of increasinHydrocarbons of increasing molecular mass are superior giving lots of energy due tog molecular mass are superior giving lots of energy due to large amounts of
large amounts of bonds, uncompressed (hydrogen)gases are inferior bonds, uncompressed (hydrogen)gases are inferior ∆
∆ Hc(CHc(C88HH1818) = –5510kJmol) = –5510kJmol –1 –1 density 0.703gcmdensity 0.703gcm –3 –3 Calculate the calorific value per gram and per Calculate the calorific value per gram and per cmcm33
1 mole C
1 mole C88HH1818= = 111144gg 11ccmm33of of ococtatane ne hahas a s a mamass ss of of 0.0.70703g3g 11114g 4g of of ococtatane ne yiyielelds ds 55551010kJ kJ on on cocombmbusustitionon
1g yields 5510kJ/114g = 48.3kJg
1g yields 5510kJ/114g = 48.3kJg –1 –1= = ccaalloorriiffiic c vvaalluuee 11ccmm33yields 0.703g x 48.3kJgyields 0.703g x 48.3kJg –1 –1= 34.0kJcm= 34.0kJcm –3 –3= calorific value= calorific value
5
5 Give rise to harmleGive rise to harmless combustion products (lss combustion products (little pollution)ittle pollution)
Hydrocarbons can give CO(poisonous) and carbon(soot) if there’s insufficient air or fuel is not
Hydrocarbons can give CO(poisonous) and carbon(soot) if there’s insufficient air or fuel is not correctly mixedcorrectly mixed High temp of combustion can form toxic
High temp of combustion can form toxic nitrogen oxides from the air used nitrogen oxides from the air used to burn the fuel:to burn the fuel: NN22(g) + O(g) + O22(g)(g) 2NO(g)2NO(g) followed infollowed in
atmosphere by
atmosphere by 2NO(g) + O2NO(g) + O22(g)(g) 2NO2NO22(g)(g)contributing to formation of acid rain, as nitric acid and contributing to formation of acid rain, as nitric acid and by oxidising sulphur dioxide toby oxidising sulphur dioxide to
sulphuric acid sulphuric acid (1)(i)Wr
(1)(i)Write the ite the full structural formula of buta-1,3-dienefull structural formula of buta-1,3-diene (ii)Give structural formula of product of
(ii)Give structural formula of product of reaction of buta-1,3-diene with alkalinereaction of buta-1,3-diene with alkaline solution of potassium
solution of potassium manganate(VIImanganate(VII)) (i)(i)
HH HH C C C C C C C C HH HH HH HH (ii)(ii) H H H H H H H H C C C C C C C C HH HH OO HH OO HH OO HH OO HH (2)(a)Expla
(2)(a)Explain the difference in in the difference in reactivity of ethane and ethene with bromine in terms bondingreactivity of ethane and ethene with bromine in terms bonding (a)Ethane
(a)Ethane single single bonds/sigma bonds/sigma only only • • C-H C-H must must be broken be broken • • Ethene aEthene also has lso has sigma sigma and pi and pi bonds bonds • • where where electrons electrons are morare moree accessible/pi bond is weaker(and breaks)
accessible/pi bond is weaker(and breaks) (3)(a)State
(3)(a)State with rwith reason the eason the empirical empirical formula formula of polyof polypropene propene (a)CH(a)CH22 as polymer made by addition reaction/no loss of small moleculesas polymer made by addition reaction/no loss of small molecules (4)
(4)(a)(a)WrWrite eite equaquatiotion for cn for compompletlete come combusbustiotion of hyn of hydrodrogengen (a)(a)2H2H22 + O+ O22→→2H2H22OO (b)Why does methane not react with air unless a
(b)Why does methane not react with air unless a flame or spark is applied to flame or spark is applied to the mixture?the mixture? (b)
(b) • • Activation Activation energy neenergy needed • eded • before rbefore reaction can eaction can proceed at proceed at reasonable rreasonable rateate (5)What does m
(5)What does methane do in the ethane do in the industrial produindustrial production of ammoniction of ammonia? (5) a? (5) • Source of hy• Source of hydrogen drogen • • Source of heat Source of heat (energy)to run (energy)to run processprocess (6)(i)Draw the structural formula of a compound which is an
(6)(i)Draw the structural formula of a compound which is an isomer of but-2-ene but which does not isomer of but-2-ene but which does not show geometric isomerismshow geometric isomerism (ii)Explain why the isomer drawn in (i) does not
(ii)Explain why the isomer drawn in (i) does not show geometric isomerismshow geometric isomerism
(6)(i) (6)(i) H H C C HH C C CC H H HH H H CC HH C C CC H H CC HH 22 55 33 33 33 H C C C H H C C C H H H HH CC HH HH C H C H C H C H C H C H C H C H 22 22 22 22
(ii)One end of C=C bond has
(ii)One end of C=C bond has 2 identical atoms/groups attached OR if cyclobutane, no C=C2 identical atoms/groups attached OR if cyclobutane, no C=C (7)Draw full structural formulae for
(7)Draw full structural formulae for
(i)The organic product of the reaction of ethene
(i)The organic product of the reaction of ethene CC22HH44 withwith (aq)potassium manganate(V
(aq)potassium manganate(VII) and II) and HH22SOSO44 (ii)3,4-dimethy1hex-2-ene (ii)3,4-dimethy1hex-2-ene (7)(i) (7)(i) H C C H H C C H O H O H O H O H HH HH (ii) (ii) H C C C C C C H C C C C C C HH HH HH HH HH HH HH HH HH HH HH CC CC HH HH HH HH (8
(8)()(a)a)StStatate e ththe e rerelalatitiononshship ip bebetwtweeeen n 2,2,2,2,4-4-trtrimimetethyhylplpenentatane ne anand d ococtatanene (a(a)s)strtrucuctuturaral l isisomomererss (b)Octane has to be vaporised before burning in an engine.
(b)Octane has to be vaporised before burning in an engine. Determine fuel to air ratio by volume for complete combusDetermine fuel to air ratio by volume for complete combustion of octane(g)tion of octane(g) (b)2C
(b)2C88HH1818 + 25O+ 25O22 →→16CO16CO22 + 18H+ 18H22OO aaiir r iis s 2200%%OO22 tthheerreeffoorree 22::112255 (c)Lead tetraethyl used to be added to petrol
(c)Lead tetraethyl used to be added to petrol to boost its Relative Octane Number but this has to boost its Relative Octane Number but this has now been replaced by compounds such asnow been replaced by compounds such as benzene or MTBE(not so effective as the lead
benzene or MTBE(not so effective as the lead compound and so need compound and so need to be added in to be added in larger quantities causing solubility problems)larger quantities causing solubility problems) (i)Why has the addition of lead tetraethyl to petrol been stopped
(i)Why has the addition of lead tetraethyl to petrol been stopped in the UK? (i)lead is poisonous/ruins catalyst in catalytic convertersin the UK? (i)lead is poisonous/ruins catalyst in catalytic converters (ii)How might the difficulty in keeping MTBE in solution in the petrol cause
(ii)How might the difficulty in keeping MTBE in solution in the petrol cause a problem in the running a problem in the running of the car?of the car? (ii)RON may not be maintain
(ii)RON may not be maintained OR ed OR fuel can cause knocking/pre-ignitiofuel can cause knocking/pre-ignitionn (iii
(iii)Apa)Apart frort from solum solubilibility, sty, state otate one prone problem blem assocassociateiated with d with the usthe use of bene of benzene azene as an ads an additivditive to pee to petroltrol (ii(iii)beni)benzene is zene is carccarcinogeinogenicnic (9)(a)Draw a diagram to show the shape
(9)(a)Draw a diagram to show the shape of the chloromethane molecule and explain why it has of the chloromethane molecule and explain why it has this shapethis shape (b)Explain why the Bt of chloromethane is higher than that
(c)Explain why the Bt of methanol is higher than
(c)Explain why the Bt of methanol is higher than that of chloromethanethat of chloromethane
(a) (a) CC CC ll HH HH HH
(a)4 pairs of electrons around C
(a)4 pairs of electrons around C arranged to minimise repulsionarranged to minimise repulsion (b)chlorometha
(b)chloromethane has ne has a (permanent)dipolea (permanent)dipole,, methane only has van der methane only has van der Waals forcesWaals forces •
• attraction(fattraction(forces) betweeorces) between dipolesn dipoles stronger than Vdw in CHstronger than Vdw in CH44 Increase in number of electrons in Increase in number of electrons in molecule, causesmolecule, causes increase in VDW forces of attraction between molecules
increase in VDW forces of attraction between molecules (c)H bonding in
(c)H bonding in methanol between molecules stronger than dipole-dipole/VDW forcesmethanol between molecules stronger than dipole-dipole/VDW forces (10) Ethane and chlorine react when exposed
(10) Ethane and chlorine react when exposed to lightto light
step 1 step 1 CC H H + + C l C l C H C H C C + + H H C lC l HH HH HH HH CC HH 33 33 step 2 step 2 CC + + CC l l CC l l C H C H C C C lC l ++ C lC l HH HH HH HH CC HH 33 33
(a)Explain the movement of the C-H bond electron pair in (a)Explain the movement of the C-H bond electron pair in step 1step 1
(a)1 electron goes to the C atom (to form a radical) the other goes to form a bond with the Cl atom (a)1 electron goes to the C atom (to form a radical) the other goes to form a bond with the Cl atom Haloalkanes
Haloalkanes CCnnHH2n + 12n + 1XX Compounds formed when a member of the Compounds formed when a member of the halogen group is substituted into an alkanehalogen group is substituted into an alkane
Nu
Numbember r indindicaicatinting g halhalogeogen pn posiositiotion n on on C C chachain- in- halhalogeogen n namname- e- alkalkane ane namname e HH || Cl–C–Cl Cl–C–Cl || Cl Cl trichloromethane trichloromethane H H H H HH | | | | || H–C–C–C–H H–C–C–C–H | | | | || H H I I HH 2-iodopropane 2-iodopropane CH
CH33CCll CChhlloorroommeetthhaannee CCaarrbboonn––HHaallooggeen n bboonnd d iis s ppoollaar r
\\δ+ δ– δ+ δ– –
– CCX (halogen more EN than carbon)X (halogen more EN than carbon) // displacement of bonding electron pair displacement of bonding electron pair CH
CH33CHCH22BBrr BBrroommooeetthhaannee
CH
CH33CHCH22CHCH22BBrr 11--bbrroommoopprrooppaannee
CH CH33CHBrCHCHBrCH33 2-bromopropane2-bromopropane CH CH22Br Br || CH CH33 –CH–CH –CH–CH33 1-bromo-2-methylpropane 1-bromo-2-methylpropane CH CH33 || CH CH33 –C–CH –C–CH22 –Br –Br || CH CH33 1-bromo-2,2-dimethylpropane
1-bromo-2,2-dimethylpropane 1,3-dimethylcyclopentane1,3-dimethylcyclopentane
F F Br Br | | || F–C–C–H F–C–C–H | | || F F ClCl 2-bromo-2-chloro-1,1,1-trifluoroethane 2-bromo-2-chloro-1,1,1-trifluoroethane Functional group
Functional group An atom/group of atoms/structural feature in a molecule which has chemical properties not shown by An atom/group of atoms/structural feature in a molecule which has chemical properties not shown by anan alkane(determi
alkane(determines nes reactions)reactions) -
- All reactions of haloalkanes are reactions of the halogen atom(fAll reactions of haloalkanes are reactions of the halogen atom(functional group) Atoms other than C and H are more reactive thanunctional group) Atoms other than C and H are more reactive than hydrocarbon chain which can only react like alkanes
hydrocarbon chain which can only react like alkanes. . Carbon–halogen bond easier to break than C–H bondsCarbon–halogen bond easier to break than C–H bonds Structural isomerism
Structural isomerism • • Moving the halogeMoving the halogen atom to diffn atom to different positions oerent positions on the C chain n the C chain • • Branching of tBranching of the C chain in lahe C chain in larger moleculesrger molecules Hydrocarbon chain to which a functional group is
Hydrocarbon chain to which a functional group is attached can exist in one of attached can exist in one of 3 possible forms3 possible forms R
R 11R R 22R R 33are alkyl groups which maybe the same or are alkyl groups which maybe the same or different but must contain at least one different but must contain at least one C atomC atom
-
- Same types of reaction for all 3 types of haloalkane but difference in rate of reactionSame types of reaction for all 3 types of haloalkane but difference in rate of reaction -
- No compound with fewNo compound with fewer than 4 C atoms per molecule caer than 4 C atoms per molecule can form a tertiary C compon form a tertiary C compoundund H
H No No fefewewer tr thahan 2n 2H aH atotoms ms atattatachcheded || to to fufuncncttioionanal l grgrououp p C C aatotomm R R 11 –C–X –C–X || ––CCHH22X primary 1°X primary 1° H H H
H OOnne e H H aattoom m aattttaacchheedd || to to ffununcctitioonanal l grgrououp p C C aatotomm R R 11 –C–X –C–X || ––CCHHX sX seeccoonnddaarry 2y 2°° R R 22 R
R 33 No H atom on functional group C atom No H atom on functional group C atom
|| R R 11 –C–X –C–X || ––CCX X tteerrttiiaarry y 33°° R R 22
Rates of reaction of haloalkane depends on: Rates of reaction of haloalkane depends on:
•
• Nature oNature of the f the halogenhalogen IodidesIodides BromidesBromides ChloridesChlorides R
Reeaacct t qquuiicckkeesst t bbeeccaauussee RReeaacct t sslloowweesst t bbeeccaauussee -
- Largest Largest atoms atoms - - Smallest Smallest atomsatoms - C
- C––I I bboonnd d iis s lloonnggeer r eeaassiieer r tto o bbrreeaakk - L- Laarrggeer r bboonnd d eenneerrggyy -
- Lower Lower bond enebond energyrgy •
• Type Type of halof haloalkaneoalkane 1° compound1° compound 2° compound2° compound 3° compound3° compound R
Reeaacctts s ququiicckkeesstt RReeaacctts s sslloowweesstt -
- Haloalkanes are polarised molecHaloalkanes are polarised molecules, Mt higher than alkanes of the same length, dipole-dipole interacules, Mt higher than alkanes of the same length, dipole-dipole interactions exist between chainstions exist between chains Elimination reaction
Elimination reaction Elements of a simple Elements of a simple molecule(Hmolecule(H22O)are removed from the organic molecule and not O)are removed from the organic molecule and not replaced by any other replaced by any other
atom/group of atoms atom/group of atoms Nucleophilic substitution
Nucleophilic substitution δ+ C atom can be attacked by a nucleophileδ+ C atom can be attacked by a nucleophile OH
OH – – , CN, CN – – , NH, NH 3
3nucleophiles which react with haloalkanesnucleophiles which react with haloalkanes ::OHOH – – prprovovidides es a pa paiair or of ef elelectctrorons ns fofor Cr C C–C–Br Br bobond nd brbreaeaksks
heterolytical
heterolytically, both electrons from the bond ly, both electrons from the bond taken by Br taken by Br – – then OHthen OH – – bonds to Cbonds to C
Test for haloalkanes
Test for haloalkanes nucleophilic substitution reactionnucleophilic substitution reaction •
• Warm halWarm haloalkane with oalkane with NaOH(aq)NaOH(aq) CCnnHH2n + 12n + 1X + OHX + OH – – (nucleophile)(nucleophile) CCnnHH2n + 12n + 1OH + XOH + X – – (halide ion)(halide ion)
•
• Silver nitrate test, AcSilver nitrate test, Acidify with (dil)nitriidify with (dil)nitric acid to remove excess OHc acid to remove excess OH – – which could react with Agwhich could react with Ag++
•
• Add siAdd silver nitratlver nitrate(aq)e(aq) AgAg++(aq) + X(aq) + X – – (aq)(aq) AgX(s)AgX(s) Resu
Result:lt: - - AgClAgCl, W, White hite ppt, ppt, dissdissolves olves in in (dil(dil)NH)NH33to give a colourless solutionto give a colourless solution
-
- AgBr, Cream ppt, parAgBr, Cream ppt, partially dissolvetially dissolves in (dil)NHs in (dil)NH33but dissolves in (conc)NHbut dissolves in (conc)NH33to give a colourless solutionto give a colourless solution
-
- AgI, Yellow AgI, Yellow ppt, insoluble ippt, insoluble in NHn NH33solution of any concentrationsolution of any concentration
C–Cl bonds in compounds used as
C–Cl bonds in compounds used as herbicides, weedkilleherbicides, weedkillers for crops, insecticides, DDT, C–Cl bond is sufficiently inert to give compoundrs for crops, insecticides, DDT, C–Cl bond is sufficiently inert to give compound longish life but survival in environment causes problems as
longish life but survival in environment causes problems as DDT is toxic to insect eating birds which DDT is toxic to insect eating birds which accumulates toxic compound inaccumulates toxic compound in body fat
