1. KINETICS -REACTION RATES
AP Chem

2. RATE Dquantity / Dtime mol / L• s
Average rate of product produced = negative average rate of reactant consumed
Rate of a Rxn is always Positive
Reaction rates are determined experimentally by measuring concentrations at various times

3. Rate Laws
Equation that expresses the mathematical relationship between the rate of a rxn and the concentration of reactants
Include the specific rate constant “k”
k = numerical value that relates rxn rate & concentration of reactants at a given temp

4. Specific Rate Constant (k)
k is unique for every rxn
k will NOT change with concentration
k will change with temperature
A large k value means that the reactants rapidly form products
Units can vary depending on situation
ie: L/mol•s, L2/mol2•s, 1/s

5. General Form of Rate Laws
General Reaction:
aA + bB  products
General Rate Law:
Rate = k [A]m[B]n
(m & n = reactions orders for A and B)
Reaction Order defines how the rxn rate is affected by concentration of reactants

6. Determining Reaction Order by Method of Initial Rates
Example:

7. Integrated Rate Laws Shows how concentration depends on time
Used for aA  products
Three types of Integrated Rate Laws:
Zero Order
First Order
Second Order

8. Zero Order [A]t = -kt + [A]0 t1/2 = [A]0 / 2k
[A]0 = initial concentration
[A]t = concentration at time t
Half life – time required to reach half of original concentration
t1/2 = [A]0 / 2k

9. First Order ln[A]t = -kt + ln[A]0 ln[A]t – ln[A]0 = -kt
ln([A]t/[A]0) = -kt
t1/2 = 0.693/k

10. Second Order
1/[A]t = kt + 1/[A]0
1/[A]t – 1/[A]0 = kt
t1/2 = 1/k[A]0

11. Determining Integrated Rate Law Order Graphically
You can determine the rxn order if given [A] and time by making a graph.
Plot:
[A] vs. time
ln[A] vs. time
1/[A] vs. time
(see which graph is linear)

12. Zero Order rate is constant; doesn’t change with concentration
plot of [A] vs. time = linear
Rate=k
-k=slope

13. First Order Concentration and rate are directly proportional
Plot of ln[A] vs. time = linear
Rate = k[A]
-k=slope

14. Second Order If [reactants] doubles, rate quadruples
Plot of 1/[A] vs. time = linear
Rate = k[A]2
k=slope