Chemical Kinetics Review
The study of chemical reactions
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
Factors Influence Reaction Rates
- Concentration Effect or dependence
The dependences of rates on concentrations are called
differential rate laws: expressions of rates in terms
of concentrations of reactants - order.
Dependences of concentration on time are
Integrated rate laws:
First Order Reactions
Second Order Reactions
- Nature of Reactants: mechanism
- Temperature: activation energy
- Heterogeneous reactions: reactants are present in more than one phase.
- Catalysts: substances used to change reaction rates.
Initial rate problems
For the reaction 2 N2O5 = 4 NO2 + O2
What is the order of the reaction?
|Exprmnt ||Initial [N2O5] in M
||Rate in M/s
|expnt 1 ||1e-2 ||4.8e-6
|expnt 2 ||2e-2 ||9.6e-6
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.
13.4 Change of Concentration with Time - The integrated rate law
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?