Chapter 11 Chemical Reactions.ppt

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Chapter 11

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Section 11.1

Section 11.1

p. 344

p. 344

Describing Chemical

Describing Chemical

Reactions

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All chemical reactions…

 have two parts:

1. Reactants = substances you start with

2. Products = end with

 reactants turn into products

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- Page 346

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In a chem rxn

 Atoms not created or destroyed (Law of

Conservation of Mass)

 rxn described in a:

#1. sentence every item is a word

Copper reacts with chlorine to form copper (II) chloride.

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Symbols in equations?

products (points to products)

–Read as: “reacts to form” or yields

 plus sign = “and”

 (s) after formula = solid: Fe

(s)

 (g) = gas: CO

2(g)

 (l) = liquid: H

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Symbols used in equations

(aq) after formula = dissolved in

water, aqueous solution: NaCl_(aq) is

salt water solution

↑ used after product - indicates

gas produced: H₂↑

used after product - indicates

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Symbols used in equations

■ _{double arrow} indicates a

reversible reaction (more later)

■ shows that

heat supplied to rxn

■ indicates catalyst

supplied (here, platinum is

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What is a catalyst?



substance that speeds up

rxn, w/o being changed or

used up in rxn



Enzymes - biological or

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#3. The Skeleton Equation



Uses formulas and symbols to

describe rxn

–but doesn’t indicate how many;

means they’re NOT balanced



All chem equations are

description

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Write a skeleton equation for:

1. Solid iron (III) sulfide reacts with

gaseous hydrogen chloride to form iron (III) chloride and hydrogen

sulfide gas.

2. Nitric acid dissolved in water reacts

with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in

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Now, read these equations:

Fe_(s) + O_2(g)  Fe₂O_3(s)

Cu_(s) + AgNO_3(aq)  Ag_(s) + Cu(NO₃)_2(aq)

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#4. Balanced Chemical Equations

 Atoms can’t be created or destroyed

in an ordinary reaction:

–All atoms we start with we must

end up with (balanced!)

 balanced equation has same # of

each element

on both sides

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Rules for balancing:

1) Assemble correct formulas for all

reactants and products, using “+” and “→”

2) Count # of atoms of each type on both sides 3) Balance elements one at a time by adding

coefficients (the numbers in front) where you need more - save balancing the H and O

until LAST!

(hint: I prefer to save O until the very last)

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 Never change subscript (only change

coefficients)

– changing subscript (formula) describes different chemical

– H₂O different than H₂O₂

 Never put coefficient in middle of formula;

only in front

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Practice Balancing Examples

 _AgNO

3 + _Cu  _Cu(NO3)2 + _Ag

 _Mg + _N

2  _Mg3N2

 _P + _O

2  _P4O10

 _Na + _H

2O  _H2 + _NaOH

 _CH

4 + _O2  _CO2 + _H2O

2 2

3

4 5

2 2 2

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Balancing Equations

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Section 11.2

Section 11.2

p. 330

p. 330

Types of Chemical

Types of Chemical

Reactions

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Types of Reactions

 5 major types_.

 predict the products

 predict whether or not they will happen at all

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#1 - Combination Reactions

 Combine = put together

 2 substances combine to make one

cmpd (also called “synthesis”)

 Ca + O

2 CaO

 SO

3 + H2O  H2SO4

 predict products, especially if reactants

are 2 elements

 Mg + N

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Complete and balance:

 Ca + Cl

2 

 Fe + O

2  (assume iron (II) oxide is the product)

 Al + O

2 

 Remember first step…write

correct

formulas

subscripts at this point, but not while balancing!

 Then balance by changing just

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#1 – Combination Reactions

 Additional Notes:

a) Some nonmetal oxides react

with H₂O - produces acid: SO₂ + H₂O  H₂SO₃

b) Some metallic oxides react with

H₂O - produces base:

CaO + H₂O  Ca(OH)₂

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#2 - Decomposition Reactions

 decompose = fall apart

 one reactant breaks apart into 2 or

more elements or cmpds

 NaCl Na + Cl

2

 CaCO

3 CaO + CO2

 Note:

energy

electricity, etc.) usually required

electricity

  



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#2 - Decomposition Reactions

 predict products if binary cmpd

(made of 2 elements)

–It breaks apart into the elements:

 H

2O

 HgO

electricity

  



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#2 - Decomposition Reactions

 If cmpd has > 2 elements you must

be given one of products

–other product from the missing pieces

 NiCO

3 CO2 + ___

 H

2CO3(aq) CO2 + ___



 

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#3 - Single Replacement Reactions

 One element replaces another _(new

dance partner)

 Reactants must be an element & cmpd

 Products will be a different element

and different cmpd

 Na + KCl  K + NaCl

 F

2 + LiCl  LiF + Cl2 (Cations switched)

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#3 Single Replacement Reactions

 Metals replace other metals (they can

also replace H)

 K + AlN 

 Zn + HCl 

 Think of water as: HOH

–Metals replace first H, then combines w/ hydroxide (OH).

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#3 Single Replacement Reactions

 can even tell whether or not single replacement rxn will happen:

–b/c some chemicals more “active” than others

–More active replaces less active  list – p. 333 -

Activity Series of

Metals

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The “Activity Series” of Metals

Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead HydrogenHydrogen Bismuth Copper Mercury Silver Platinum Gold

1) Metals can replace other

metals, if they are above

metal trying to replace (i.e. Zn will replace Pb)

2) Metals above H can replace

H in acids.

3) Metals from Na upward can

replace hydrogen in H₂O Higher

activity

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The “Activity Series” of Halogens

Fluorine Chlorine Bromine Iodine

Halogens can replace other halogens in compounds, if

they are above halogen they are replacing

2NaCl_(s) + F_2(g)  2NaF_(s) + Cl_2(g)

MgCl_2(s) + Br_2(g)  No Reaction!??? ???

Higher Activity

Higher Activity

Lower Activity

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#3 Single Replacement Reactions

Practice:



Fe + CuSO

4





Pb + KCl



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#4 - Double Replacement Reactions

 Two things replace each other.

– _{Reactants must be two ionic}

compounds, in aqueous solution

 NaOH + FeCl

3 

– _{positive ions change place} (dance partners)

 NaOH + FeCl

3 Fe+3 OH- + Na+1 Cl-1

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#4 - Double Replacement Reactions

 Have certain “driving forces”, or reasons

–

_only

a) doesn’t dissolve in water & forms solid (a “precipitate”), or

b) is gas that bubbles out, or

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Complete and balance:



assume all of the following

reactions actually take place:

CaCl

+ NaOH



CuCl

+ K

S



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How to recognize which type?



Look at the

reactants

:

E + E =Combination

C

= Decomposition

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Practice Examples:

 H

2 + O2 

 H

2O 

 Zn + H

2SO4 

 HgO 

 KBr + Cl

2 

 AgNO

3 + NaCl 

 Mg(OH)

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#5 – Combustion Reactions

 Combustion means “add oxygen”

 Normally, a cmpd composed of only

C, H, (and maybe O) is reacted with oxygen – called “burning”

 Complete combustion, products are

CO₂ and H₂O

 If incomplete, products are CO (or

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Combustion Reaction Examples:

 C

4H10 + O2  (assume complete)

 C

4H10 + O2  (incomplete)

 C

6H12O6 + O2  (complete)

 C

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SUMMARY: An equation...

 Describes a rxn

 Must be balanced (follows the Law of

Conservation of Mass)

 only balance by changing coefficients  special symbols to indicate physical

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Reactions

 5 major types

 We can tell what type they are by

looking at reactants

 Single Replacement happens based on

the Activity Series

 Double Replacement happens if one

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Section 11.3

Section 11.3

p. 342

p. 342

Reactions in Aqueous Solution

Reactions in Aqueous Solution

Co(NO

Co(NO₃₃))₂₂

K

K₂₂CrCr₂₂OO₇₇ KK₂₂CrOCrO₄₄

NiCl

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Net Ionic Equations



Many reactions occur in water- that

is, in

aqueous solution



When dissolved in water, many

ionic cmpds “dissociate”, or

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Net Ionic Equations

 Example _{(needs to be a double replacement reaction)}

AgNO₃ + NaCl  AgCl + NaNO₃ 1. this is the full balanced equation

2. next, write it as ionic equation by splitting the cmpds into their ions:

Ag1+ + NO

31- + Na1+ + Cl1- 

AgCl + Na1+ + NO

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1-Note that the AgCl did not ionize, because it is a “precipitate”

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Net Ionic Equations

3. simplify by crossing out ions not

directly involved (called spectator ions)

Ag1+ + Cl1-  AgCl

This is called the net ionic equation

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Predicting the Precipitate

 Insoluble salt is a precipitate

[note Figure 11.11, p.342 (AgCl)]

 General solubility rules are found:

a) Table 11.3, p. 344 in textbook b) Reference section - page R54

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Let’s do some examples

together of net ionic

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