Topic 16 - Chemical Kinetics

Rate expression

rate = k[A]^x[B]^y

rate constant

k

overall order of reaction

x + y

order of reaction

either x (with respect to A) or y (with respect to B)

Order of reactions

zero-order: the concentration does not affect the reaction rate
first-order: order of reaction = 1 (rate is proportional to concentration)
second-order: order of reaction = 2

catalysts in activation energy

Alter a reaction mechanism by introducing a step with a lower activation energy

Reaction mechanism

A series of separate intermediate steps. All elementary steps summed together will give the overall balanced reaction.

heterogeneous reaction

a reaction involving reactants in two different phases

homogeneous reaction

a reaction whose reactants and products exist in a single phase

molecularity

the number of reactant particles involved in an elementary step

Unimolecular

describes a reaction that involves only one particle that goes on to form products

bimolecular

an elementary step in a reaction that involves two particles, either the same species or different, that collide and go on to form products

Relationship between reaction mechanism, order of reaction and rate-determining step

The slowest step in a reaction mechanism is known as the rate-determining step or the step with the highest activation energy

unit rate of reaction

mol dm-3 s-1

unit concentration

mol dm-3

Concentration-time graph zero order

Concentration-time graph first order

Concentration-time graph second order

rate-concentration graph zero order

rate-concentration graph first order

rate-concentration graph second order

Gradient of arrhenius graph

-Ea/R

y intercept (Arrhenius graph)

ln[A]

units in arrhenius equation

t = kelvin, Ea = J mol-1

What is A in the arrhenius equation

A = frequency factor (how many successful reactions occur)

What is your x value

1/T

What are the axis of an Arrhenius equation?

Y axis = ln k

\
X axis = 1/T