Another type of graph can be used when assessing rate of reaction. This graph shows the energy available in the reactant particles and indicates the proportion of them that have the required energy for a reaction.

To compare rate of reaction at different temperatures accurately the Arrhenius equation is used. A is the exponential factor, which relates to the frequency of particle collisions. K is the rate constant and is proportional to rate of reaction. ln is used to solve the Arrhenius equation to remove the 'e' from the equation, ln is a function on your calculator and you don't need to understand it further for chemistry.

A catalyst is a substance that lowers the activation energy of a reaction by providing an alternative pathway for reaction. The catalyst doesn't take part in the reaction so will not be altered or used up.

Catalysts are important to many industrial and biological reactions (inside plants or animals). Biological catalysts are given the name 'enzyme' and different enzymes are present in every cell of the human body to perform a number of vital reactions.

1

Look at this graph showing enzyme activity at different temperatures. Why does the rate of reaction fall at higher temperatures and not continue to increase?

2

What factor would result in more reactant particles being present in the reaction space?

3

In the reaction between hydrogen and nitrogen at 40C the activation energy is 162 kJ/mol and the rate constant is 2.0 x 10-9 s-1. Calculate the exponential factor (A) for this experiment at 250K.

4

What is the catalyst used in the Haber process? (the reaction between nitrogen and hydrogen to form ammonia)

5

How do catalysts affect rate of reaction using collision theory?