Chemical Kinetics

rate of reaction equation

what is a rate law?

relates the rate of a reaction to the rate constant and the concentration of its reactants

what is a zero order reaction?

• does not depend of the concentration of reactants

• Rate= k[A]⁰

• units of rate constant: M/s

what is a first order reaction?

• directly proportional to the concentration of reactants

• rate= k[A]¹

• unit of rate constant: 1/s

what is a second order reaction?

• rate of reaction increases exponentially with the concentrations of reactants

• rate= k[A]² or k[A][B], k[A]², k[B]²

• unit of rate constant: 1/Ms

unit of rate constant rule

M^1-ns^-1 where n=reaction order

0th order concentration graph

• concentrations of reactants decrease LINEARLY

1st order concentration graph

• concentration of react decreases HYPERBOLICALLY

2nd order concentration graph

• concentration decreases SHARPER HYPERBOLICALLY over time

determining the reaction order from dataset steps

For reactant A:

1. find the two trials where the concentrations of B are the same

2. divide the two concentrations of A for those trials

3. divide the two initial rates for those trials

4. write the divided concentrations to the power of x equals the divided initial rates

5. solve for x

what are integrated rate laws?

used to determine the amount of reactants or products present after a period of time

0th order integration law

[A]_t=-kt+[A]₀

unit of k= M/s

1st order integration law

ln[A]_t=-kt+ln[A]₀

unit of k= 1/s

2nd order integration law

1/[A]_t=kt+1/[A]₀

unit of k= 1/Ms

what is the rate determining step

the slowest step of the reaction mechanism and determines the overall rate law of reaction

• reactant coefficients of the RDS become the exponents of the OVERALL rate law

how to identify intermediates in a reaction mechanism?

• intermediates will NOT be present as either reactants or products

how to identify catalysts in a reaction mechanism?

catalysts will be present as BOTH reactants or products

what are the 3 requirements in the collision theory that allow for a chemical reaction to occur?

1. molecules must collide

2. molecules must be in the correct orientation during collision

3. molecules must have enough energy to overcome the activation energy barrier

arrhenius equation

describes the relationship between temperature and reaction rates

• A= frequency factor or the fraction of collisions that have enough energy to overcome the activation energy barrier

how does temperature affect activation energy?

no effect

half life time equations for varying order or reactions

0 order: t=[A]₀/2k

1 order: t=0.693/k

2 order: 1/k[A]₀

which order of reaction is radioactive decay?

1