Enthalpy (H) is a measure of the energy in a system, and the change in enthalpy is denoted by

A thermochemical equation is a balanced stoichiometric chemical equation which includes the enthalpy change.
The equations take the form:

## Thermochemical Equations for Endothermic Reactions

The sign of the

Notice that in an endothermic reaction like the one depicted above, we can think of heat as being a *reactant*, just like A and B.

## Thermochemical Equations for Exothermic Reactions

In an exothermic system, the

Notice that here, we can think of heat as being a *product* in the reaction.