How does enthalpy differ from heat?

1 Answer
May 26, 2014

Enthalpy is what is sometimes termed Chemical Energy - the potential energy locked up inside a substance as a result of its bonding.

During a exothermic reaction, the chemical energy (enthalpy) inside a substance decreases as this form of energy is transformed into heat energy, resulting in the substances and their surroundings getting hotter. Conservation of energy is satisfied. During an endothermic reaction, the enthalpy increases: the products have more chemical energy than the reactants. This energy has to come from somewhere, so it is taken from the surroundings, which lose heat energy as a result.