Reactions and temperature changes

Exothermic and endothermic reactions

When a fuel burns, the surroundings become warmer. Energy is transferred to the surroundings. This is an example of an exothermic reaction.

During some reactions, energy is transferred from the surroundings. This is called an endothermic reaction.

In endothermic reactions, energy enters. In exothermic reactions, energy exits.

Temperature change

For some reactions, it is possible to measure the temperature of the reactants at the start and the temperature of the products at the end.

The change in temperature indicates how exothermic or endothermic the reaction is.

ChangeReaction type
Increase in temperatureExothermic
Decrease in temperatureEndothermic

The slideshow describes an exothermic reaction between dilute sodium hydroxide and hydrochloric acid, and an endothermic reaction between sodium carbonate and ethanoic acid.

Sodium hydroxide solution is poured into a beaker of hydrochloric acid which contains a thermometer showing room temperature.

1. Sodium hydroxide solution is poured into a beaker of hydrochloric acid which contains a thermometer showing room temperature

A study of the energy changes involved in chemical reactions, whether exothermic or endothermic