An exothermic reaction is one that gives out energy to its surroundings, usually in the form of heat.

Everyday uses of exothermic reactions include hand warmers and self-heating coffee cans.

An endothermic reaction is one that takes in energy from its surroundings, usually in the form of heat.

An everyday use of endothermic reactions is cold packs for sports injuries.

A catalyst is a substance that speeds up the rates of chemical reactions without being used up itself.

1. They increase the speed of reactions.

2. They allow reactions to occur at lower temperatures.

3. They increase the yield of products.

4. They make processes more economical.

1. They are expensive to buy initially.

2. Different reactions require different catalysts.

3. They can become contaminated or 'poisoned'.

4. They may need regular cleaning.

Catalysts work by providing an alternative route for the reaction with a lower activation energy, meaning the minimum energy needed to start the reaction is lowered.