Energy changes in chemical reactions

Every chemical reaction involves a change in energy. During the reaction, bonds inside the substances that are reacting together must be broken and new chemical bonds must be formed in the products that are being made. There are two different types of energy change that can take place.

Exothermic reactions

Exothermic reactions involve energy being released. This energy is most commonly a release of heat energy which would be indicated by a temperature rise.

Energy could also be released in a chemical reaction in the form of a sound or light being produced but the most exciting chemical reactions will probably have all three going on!

Close-up of burning lumps of coal
Burning fuels like coal is an exothermic process

Exothermic reactions happen around us in everyday life. Fuels burning in combustion reactions involve energy being released. It doesn’t matter if it’s a small object like a match or a whole bonfire that is burning, both heat energy and light energy are given out.

Not every exothermic reaction is as exciting as a combustion reaction. When acids and alkalis react together, the energy released is not as obvious. Mixing the two solutions and stirring results in a small increase in the temperature of the reaction mixture.

Endothermic reactions

An endothermic reaction is one in which heat energy is taken in. Normally this is shown by a drop in temperature.

Chemical cool pack being applied to ankle

There are fewer examples of endothermic reactions in everyday life. Chemical cold packs that are used to treat bumps and sprains use an endothermic reaction to cool down. Squeezing the cold pack bursts a small inner bag allowing two chemicals to mix. The result is an endothermic reaction that cools the pack down and it can be used to stop or reduce swelling.

Move on to Test
next