An understanding of the energy involved in chemical reactions is important in the chemical industry.

Endothermic reactions that take in energy may generate additional costs through heating the reaction to ensure that the rate remains high enough.

Some exothermic reactions require no additional heating. In some cases, the energy given out by the reaction is so great, that the heat source can be removed once the reaction has begun.

The temperature must be monitored to ensure that the energy given out during the process doesn’t cause the temperature of reaction vessels to rise to unsafe levels.

The chemical energy involved in a reaction is also called the enthalpy. Chemical reactions involve an enthalpy change:

  • Energy is used breaking bonds
  • Energy is released when new bonds form

This means that the enthalpy change is the difference in energy between the products and the reactants.

The enthalpy change takes the form of heat given out or absorbed. The heat energy given out or taken in by one mole of a substance can be measure in either joules per mole (J mol-1) or more commonly kilojoules per mole (kJ mol-1).