AP Chemistry/Kinetics

TERMINOLOGY

Rate of reaction - change of concentration of reactants/products per unit time

Activation energy - energy required to break the bonds of the reactants at the start of the reaction Rate equation - experimentally determined equation showing the relationship between the rate constant and concentrations of reactants raised to their               respective powers

Order of reaction(with respect to a reactant) - is the power to which the reactant concentration is raised in a rate equation

Overall order of reaction - sum of powers to which concentrations of reactants are raised in a rate equation

Rate constant - proportionality constant whose magnitude shows how fast the reaction proceeds

Reaction mechanism - series of steps undergone by a reaction

Rate determining step - slowest step in the reaction mechanism of a reaction

Catalysis - process of speeding up the rate of a reaction using a catalyst. It involves the lowering of activation energy

Homogeneous catalysis - catalysis using a catalyst which is in the same phase with reactants e.g the reaction of S2O82- with I- catalysed by Fe2+ or Fe3+ in an aqueous state as shown below:

S2O82- + 2I- → I2 + 2SO42-

Using Fe3+ : 1. 2Fe3+ + 2I- → I2 + 2Fe2+ 2. 2Fe2+ + S2O82- → 2Fe3+ + 2SO42-

WORKED EXAMPLE

1 The mechanism of a reaction is as shown below:

H2O2 + I- → H2O + IO- (slow)

H+ + IO- → HIO (fast)

HIO + H+ + I- → H2O + I2 (fast)

a Deduce the equation of the reaction

b Write down the rate equation

ANSWER

1(a) step1: cancel out what appears on both sides of the reaction mechanism step2: equate what remains on the LHS to what remains on the RHS:

H2O2 + 2I- + 2H+ → 2H2O + I2

b rate equation: k[H2O2].[I-]. *{taken from the slowest step/rate determining step}