# Chemical Kinetics Review

The study of chemical reactions

# Reaction Rates

Chemical reaction rates are the rates of change in concentrations or amounts of either reactants or products.

Units for changes in amounts: mol/s, g/s, lb/s, kg/day etc.

Units for changes in concentrations: mol/(L s), g/(L s), %/s etc.

Rates can be average rates, instantaneous rates, or initial rates.

# Factors Influence Reaction Rates

1. Concentration Effect or dependence on cencentration

The dependences of rates on concentrations are called differential rate laws: expressions of rates in terms of concentrations of reactants - order.

2. Dependences of concentration on time are Integrated rate laws:
First Order Reactions
Second Order Reactions

3. Nature of Reactants: mechanism

4. Temperature: activation energy

5. Heterogeneous reactions: reactants are present in more than one phase.

6. Catalysts: substances used to change reaction rates.

# Initial rate problems

Example 13.3.4 For the reaction 2 N2O5 = 4 NO2 + O2

Exprmnt Initial [N2O5] in M Rate in M/s
expnt 1 1e-2 4.8e-6
expnt 2 2e-2 9.6e-6
What is the order of the reaction?

Solution

Example

Derive the rate law for the reaction A + B + C => products from the following data, where is measured as soon as the reactants are mixed.
Experiment1234
[A]o0.1000.2000.2000.100
[B]o0.1000.1000.3000.100
[C]o0.1000.1000.1000.400
rate0.1000.8007.2000.400

Solution

# 13.4 Change of Concentration with Time - The integrated rate law

Example 13.5

The reaction 2 N2O5 = 4 NO2 + O2 is first order, with k = 4.8 s-1 at some T. If the initial concentration is 2.00e-2 M, what is the concentration after 10 min? How long will it take for the concentration of N2O5 to reduce to 1.00e-2 M from its initial concentration?