1. Unit 6: Kinetics
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2. Chemical Kinetics Thermodynamics – does a reaction take place?
Kinetics – how fast does a reaction proceed?
Reaction rate is the change in the concentration of a reactant or a product with time (M/s).
reactants products
A B
rate = -
D[A] Dt
D[A] = change in concentration of A over
time period Dt
rate =
D[B] Dt
D[B] = change in concentration of B over
time period Dt
Because [A] decreases with time, D[A] is negative.

3. A B
rate = -
D[A] Dt
rate =
D[B] Dt

4. Br2 (aq) + HCOOH (aq) 2Br- (aq) + 2H+ (aq) + CO2 (g)
red-brown
Br2 (aq) + HCOOH (aq) Br- (aq) + 2H+ (aq) + CO2 (g)
time
393 nm
light
Detector
t1< t2 < t3
D[Br2] a D Absorption

5. Br2 (aq) + HCOOH (aq) 2Br- (aq) + 2H+ (aq) + CO2 (g)
slope of
tangent
slope of
tangent
slope of
tangent
average rate = -
D[Br2] Dt
= -
[Br2]final – [Br2]initial
tfinal - tinitial
instantaneous rate = rate for specific instance in time

6. measure DP over time
2H2O2 (aq) H2O (l) + O2 (g)
PV = nRT
P = RT = [O2]RT n V
[O2] = P RT 1
rate =
D[O2] Dt RT 1 DP Dt =

8. Reaction Rates and Stoichiometry
2A B
Two moles of A disappear for each mole of B that is formed.
rate = -
D[A] Dt 1 2
rate =
D[B] Dt
aA + bB cC + dD
rate = -
D[A] Dt 1 a
= -
D[B] Dt 1 b =
D[C] Dt 1 c =
D[D] Dt 1 d

9. 13.1
Write the rate expressions for the following reactions in terms of the disappearance of the reactants and the appearance of the products:

10. 13.2
Consider the reaction
Suppose that, at a particular moment during the reaction, molecular oxygen is reacting at the rate of M/s.
At what rate is N2O5 being formed?
At what rate is NO2 reacting?

11. Review of Concepts
Write a balanced chemical equation for a gas-phase reaction whose rate is given by