Chemical Kinetics
Chemical Kinetics – the study of the rates of chemical reactions (how quickly or slowly they
occur)
Rates of reactions are based on several factors:
1. Concentration of reactants
If you increase the concentration of one or more of the reactants, the rate of the reaction
will increase
2. Temperature
If you increase the temperature of the system, the rate of the reaction will increase
3. Catalysts
Addition of a catalyst speeds up many reactions (depends on the reaction and the catalyst)
4. Surface area of solid or liquid reactants or catalysts
If the surface area of a solid or liquid is increased, the rate of the reaction will increase
Reaction Rates
AB
0 minutes
10.0 mol A
0.0 mol B
20 minutes
6.0 mol A
4.0 mol B
40 minutes
3.0 mol A
7.0 mol B
60 minutes
2.0 mol A
8.0 mol B
** NOTE – Each beaker contains a TOTAL of 10 mol**
Rate of Reaction – a measure of how quickly reactants are used up and/or a measure of
quickly products are produced
The equations needed to determine the Rate of Reaction are:
1. Rate of Appearance of a Products:
Reaction Rate =
𝛥 𝑚𝑜𝑙 (𝑜𝑟 𝑀) 𝑜𝑓 𝐵
𝛥 𝑡𝑖𝑚𝑒
2. Rate of Disappearance of a Reactant:
Reaction Rate = -
𝛥 𝑚𝑜𝑙 (𝑜𝑟 𝑀) 𝑜𝑓 𝐴
𝛥 𝑡𝑖𝑚𝑒
There are a number of ways to measure the Rates of Reactions:

Instantaneous Rate of Reaction – measures the rate of a reaction at a specific time during

the reaction
Average Rate of Reaction – measures the rate of a reaction over a specific time interval
during the reaction
We are going to focus on Average Rates of Reactions since there are more applications for this process.
Average Rates of Reactions
To measure the average rate of a reaction, you need to know the length of the time interval and change in the
concentration over that interval. Data like the ones given in the first example of these notes (see beaker
diagrams on first page) is the type of data we need for this.
Practice Problem #1:
AB
0 minutes
1.0 mol A
0.0 mol B
20 minutes
0.60 mol A
0.40 mol B
40 minutes
0.30 mol A
0.70 mol B
Using the information above, calculate the following:
a) the rate of the reaction of the product B for
the time interval of 0 to 20 minutes
b) the rate of the reaction of B for the interval of
20 to 40 minutes
60 minutes
0.20 mol A
0.80 mol B
d) the rate of the reaction of B for the time
interval of 0 to 60 minutes
e) the rate of the reaction of A for the time
interval of 0 to 60 minutes
c) the rate of the reaction of B for the time
interval of 40 to 60 minutes
Practice Problem #2:
C4H9Cl + H2O  C4H9OH + HCl
We prepare a 0.100M solution of C4H9Cl in H2O and measure the concentration of C4H9Cl at various
times during the reaction. Using the information below, calculate the average rate of disappearance of
C4H9Cl for each time interval.
Time (s)
C4H9Cl (M)
0.0
0.100
100.0
0.0820
200.0
0.0671
300.0
0.0549
Practice Problem #3:
In the reaction N2 + 3H2  2NH3, the rate of disappearance of H2 is 1.3 x 10-4 mol/L∙s. What is the rate
of appearance of NH3?