Reactions and temperature changes

When a chemical reaction happens, energy is transferred to or from the surroundings. For example, changes in heat energy happen in the following situations:

When these reactions happen in solution, there are temperature changes that can be observed. These can be measured using a thermometer.

Reactions can be endothermic or exothermic. The table shows some differences.

EndothermicExothermic
Heat energyTaken inGiven out
Temperature of reaction mixtureDecreasesIncreases

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

In endothermic reactions, energy enters from the surroundings. In exothermic reactions, energy exits to the surroundings.

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

What an exothermic and an endothermic reaction is, and how temperature changes can be used to identify which reaction is which