Chemistry GCSE

Exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings.  Reversable reactions are where the products can react to remake the orginal reactants. If the forward reaction is exothermic, the reverse reaction is endothermic.

When a chemical reaction occurs, energy is transferred, to or from, the surroundings- and there is often a temperature change. For example when a bonfire burns it tranfers heat to the surroundings. Objects near the bonfire become warmer

Exothermic reactions:

These are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. The temperature increase can be detected using a thermometer. Some examples of exothermic reactions are:

• burning
• the reaction between water and calcium oxide

Endothermic reactions:

These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. Some examples of endothermic reactions are:

• electrolysis
• the thermal decomposition of calcium carbonate in a blast furnace