**Kinetics**

**⇒** THE RATE OF CHEMICAL REACTIONS
Rate of Reactions is affected by: Surface Area of a Solid Reactant
Temperature
Pressure of gaseous reactants
Catalyst
Concentration of a reactant in Solution
DEFINITION OF A RATE OF A CHEMICAL REACTION; change in concentration of a substance
time
Unit: moldm-3s-1
NB: the use of square brackets denotes concentration e.g. [HCl]
Measuring Rate of Reactions
Some techniques for doing this are:
1.Gas syringe.
2.Volumetric analysis - samples are removed at regular intervals.
3.Measuring changes in pressure (for gas reactions)
4.Colorimeter
5.A conductivity meter
The rate at a particular instant in a reaction can be determined by
finding the gradient of a tangent on a concentration versus time curve
at that time. The gradient at t=0 is called the initial rate and is used to calculate k.
THE RATE EXPRESSION
The rate equation, the rate constant and the orders of reaction can only be worked out experimentally.
Consider the chemical equation A + B → products
Rate expression: rate α [A]m[B]n
GENERAL RATE EQUATION: rate = k [A]m[B]n
The individual order is the power to which a concentration is raised in the rate
The overall order of a reaction is the sum of all the individual orders in the rate equation eg = m + n
k is the rate constant - it’s unique to each reaction and conditions, units
depends on order of reaction.
The rate constant, k, increases exponentially with increasing temperature.