Chemistry 1 - Chapter 19 Reaction Rates and Equilibrium
19.1 Rates of Reaction
_________ – a measure of the ___________of any change that occurs within an interval of time.
Reaction Rate - ______________________________________________________
Some reactions go very fast (burning) and others go very slowly (rusting).
Collision Theory: In order to react, ___________or____________ particles must collide with
sufficient energy (called the ________ _ __ _____) and with the proper molecular orientation. If the colliding particles do not have either of these two prerequisites,
______________________________________.
o What is the energy of the reactants?
o What is the energy of the products?
o What is the activation energy?
o What is the energy of the activated complex?
o What is the ∆H? (Is it endothermic or exothermic?)
Activated complex- (also called ______________ _________)- high energy temporary arrangement of atoms that forms when particles collide with ___________________ ____________.
Factors that affect reaction rate:
1. ____________________- Reactions go faster at higher temperatures. Particles have more ______________ ____________. More colliding particles have enough energy to overcome the activation energy barrier.
2. _____________________- Increasing the concentration of reactants usually ___________ the reaction rate. If there are more particles to collide, there should be a greater number of collisions that produce products.
3. ______________ _________- Increased surface area _______________ reaction rate. Again, more particles collide.
4. ___________________- A catalyst is a substance that ______________ a reaction by lowering the ______________ __________ barrier. It is not a product or reactant and it is not used up or
changed itself.
Enzyme-
In your own words, explain what rate is.
In your own words, explain what activation energy is.
Inhibitor- __________________________________________________________
Rate Law- equation that is written that expresses how the ______________ ______ of a particular reaction is dependent upon the _____________________ of its reactants.
For the reaction aA + bB cC + dD , the general form of the rate law would be: Rate = k [A]x[B]y
Rate is usually expressed as ____________
k is the ______________ __________ _____________. It is constant for a given reaction at a given temperature. The faster a reaction, the ______________ the k value.
[A] and [B] represent the ____________________ of reactants A and B in moles per liter (M).
x and y are the order of the reactant. They can only be determined by analyzing
________________ _______. These exponents are usually positive ________________.
Determining the order of a reactant (We must use experimental data for this!):
If doubling the initial [ ] of a reactant causes the initial rate to:
___________, the reaction is _________ __________ in that reactant.
_____________, the reaction is ___________ ______________ in that reactant.
increase _____________, the reaction is __________________________in that reactant.
If doubling the initial [ ] of a reactant __________ ______ __________ the initial rate, the reaction is ___________________________ in that reactant and that reactant is removed from the rate law.
The exponents determine the order of the reactants. The sum of the exponents is the _______ __________ ___________.
Rate = k[A][B]2 is ___________ order in A, ___________ order in B, and ________ order overall. The units of k can be calculated.
What is the overall order of each of the following?
Rate = k[A]3[B]2 _______ Rate = k[A]2[B] ________
A B 2A + B 2C
Trial [A] Rate Trial [A] [B] Rate
1 0.05 3 x 10-4 1 0.1 0.2 0.10
2 0.10 1.2 x 10-3 2 0.1 0.4 0.20
3 0.20 4.8 x 10-3 3 0.2 0.4 0.80
Rate Law: Rate Law:
A + B C NH4+ + NO2- N2 + 2H2O
Trial [A] [B] Rate Trial [NH4+] [NO2-] Rate(mol/Lmin)
1 0.10 0.20 1.0 x 10-5 1 0.100 0.005 1.35 x 10-7
2 0.20 0.20 1.0 x 10-5 2 0.100 0.010 2.70 x 10-7
3 0.20 0.40 2.0 x 10-5 3 0.200 0.010 5.40 x 10-7
Rate Law: Rate Law:
Value of k:
What happens when zero is an exponent?
Reaction Mechanisms
A ____________ _____________ is a series of steps (reactions) that make up the overall reaction. Most reactions do not occur in a single step but are the ___________ ____ _________________steps.
Rate-limiting or rate-determining step -___________________________________ ________________________________________
Mechanisms are usually not completely known because of the short life of their “temporary products”. Possible mechanisms must:
1. agree with the rate law and 2. add up to the overall reaction
19.2
19.2
EQUILIBRIUM
EQUILIBRIUM
_______________ equilibrium- state where concentrations of products and reactants ______________ ____________
-equilibrium is _______________
-any chemical reaction in a _____________ _____________ will reach equilibrium -at equilibrium, ___________________________=_____________________________
jA + kB lC + mD [ ] = ___________________________
Kc = K = Keq = __________________________ (used interchangeably)
Ex. 4 NH3 + 7 O2 4 NO2 + 6 H2O
If we know equilibrium concentrations, we can calculate the equilibrium constant, Kc.
K changes with _______________________ (not with __________________ or K changes with _______________________ (not with __________________ or __________________).
__________________).
Concentrations of pure solids and pure liquids are Concentrations of pure solids and pure liquids are notnotincluded in ___________________ included in ___________________ expressions because they are ________________.
expressions because they are ________________.
CaCO3(s) CaO (s) + CO2(g) Keq = _______________
A value for K __________________ means that the equilibrium is far to the right (mostly products).
A value for K __________________ means that the equilibrium is far to the left (mostly reactants).
Example: Analysis of an equilibrium mixture of nitrogen, hydrogen and ammonia contained in a 1 L flask at 300oC gives the following results: hydrogen: 0.15 mol, nitrogen: 0.25 mol, ammonia: 0.10 mol. Calculate Keq.
3H2(g) + N2(g) 2NH3(g)
Example: Calculate the value of Keq for the following reaction at equilibrium.
HC2H3O2 (aq) + H2O (l) C2H3O2- (aq) + H3O+ (aq)
An analysis of the equilibrium mixture gives the following results:
[HC2H3O2] = 0.25 M, [C2H3O2-] = 0.075 M, [H3O+] = 6.0 X 10-5 M
LeChatelier's Principle
When a stress is applied to a system, the equilibrium will _____________________________________ ____________________________________.
Changes in concentration
An ________________ in concentration of:
o A ______________ will cause equilibrium to shift to the ____________ to form more products.
o A ______________ will cause equilibrium to shift to the __________ to form more reactants.
A __________________ in concentration of:
o A __________________ will cause equilibrium to shift to the ______________ to form more products.
o A ________________ will cause equilibrium to shift to the _______________ to make more reactants.
A + B C + D Example: As4O6 + 6C As4 + 6CO
Remove A or B Addition of CO
Add C or D Addition of C
Remove C or D Addition of As4O6
Add A or B Removal of As4
Change in Temperature
Treat _______________ as a product or react and temperature changes work just like changes in ____________________!
An increase in temperature of an _________________ reaction (H is negative) will cause equilibrium to shift to the _____________.
A _________________ in temperature of an exothermic reaction will cause equilibrium to shift to the _____________.
An increase in temperature of an ____________________ reaction (H is positive) will cause equilibrium to shift to the ____________.
A _______________ in temperature of an endothermic reaction will cause equilibrium to shift to the __________.
Example: N2 + O2 2NO H = 181 kJ
a. addition of heat b. lower temperature
Example: 2SO2 + O2 2SO3 H= -198 kJ Example: CaCO3 + 556 kJ CaO + CO2 a. increase temperature a. decrease temperature
b. remove heat
Summarize what happens when you change concentration.
Changes in pressure
Changes in pressure only affect equilibrium systems having
__________________________________ ______________________.
_____________ the pressure of a gaseous system will cause equilibrium to shift to the side with _____________ gas particles.
__________________ the pressure of a gaseous system will cause equilibrium to shift to the side with _____________ gas particles.
If the system has the same number of ____________________________ on each side, changes in pressure do not affect equilibrium.
The addition of an ____________ (nonreactive) gas does not affect the equilibrium system since the partial pressures of the gases involved in the reaction _____________________________.
Example: P4(s) + 6Cl2(g) 4PCl3(l) Example: PCl3(g) + Cl2(g) PCl5(g) a. increase container volume a. decrease container volume
b. decrease container volume b. add helium gas c. add argon gas
Example: PCl3(g) + 3NH3(g) P(NH2)3(g) + 3HCl(g) a. increase container volume
Addition of a catalyst
Adding a catalyst ___________ ________ affect equilibrium. Catalysts ___________ _____ the forward and reverse reactions equally.
Example: CO(g) + H2O(g) H2(g) + CO2(g) H = -41kJ
Determine in which direction the reaction will shift when each of these stresses are added.
a. temperature is increased b. helium gas is added c. water vapor is added
d. gaseous carbon dioxide is removed e. a catalyst is added
Example: 2SO3(g) 2SO2(g) + O2(g) H = 197 kJ
Determine in which direction the reaction will shift when each of these stresses are added.
a. oxygen gas is added
b. pressure is increased by decreasing volume
c. argon gas is added. d. temperature is decreased.
e. gaseous sulfur dioxide is removed.
Example: Consider the reaction 2NO2(g) N2(g) + 2O2(g) which is exothermic. A vessel contains
NO2(g), N2(g), and O2(g) at equilibrium. Predict how each of the following stresses will affect the concentration of O2 and the value of K.
a. NO2 is added b. N2 is removed c. The volume is halved
d. He(g) is added
e. The temperature is increased f. A catalyst is added
19.3
Entropy, Enthalpy, and Gibbs Free Energy
Spontaneous process -_______________________________________________________ May be ________ or _____________
Entropy, S - ______________________________________________________________
-associated with ____________________ (There are more ways for something to be disorganized than organized.)
Entropy _______________ going from a solid to a liquid to a gas.
Entropy increases when __________________ are formed.
Entropy _______________ in a reaction when more atoms or molecules are formed.
The entropy of a substance increases with ________________________.
________________________________________ - In any spontaneous process there is always an increase in the entropy of the universe. The energy of the universe is constant but the entropy of the universe is increasing.
Remember that we calculate the change in____________________ (heat) by subtracting the reactants’ value from the value of the products. They are given in kilojoules/mol. Remember that the enthalpy of a free element in its standard state is _________________.
Ho =__________________________________
Ex. Calculate the change in enthalpy for the reaction 2H2(g) + O2(g) 2H2O(l). Enthalpy values: H2 = 0 kJ, O2 = 0 kJ, H2O = -285.8 kJ
Gibbs free energy, G = ______________________________________________
Go = standard free __________________________
-change in free energy that occurs if the reactants in their standard states are converted to products in their standard states
Go =Ho -T So
A spontaneous reaction has a _________________ G. For example, when ice melts H is positive (endothermic), S is positive and G = 0 at 0oC.
If:
Entropy, ΔS Enthalpy, ΔH Spontaneity
