Exothermic and Endothermic Reactions

Exothermic and Endothermic Reactions

Chemical reactions either release energy to the surroundings (exothermic) or take energy in from the surroundings (endothermic) — you can usually tell which by the temperature change.

Exothermic reactions

An exothermic reaction transfers energy to the surroundings, so the temperature increases. Combustion and neutralisation reactions are both exothermic.

Endothermic reactions

An endothermic reaction takes in energy from the surroundings, so the temperature decreases. Thermal decomposition is a common example.

Practice

A student mixes two chemicals and the test tube feels cold. Was the reaction exothermic or endothermic?