We can define enthalpy as a concept used in science and engineering when heat and work need to be calculated or simply the sum of the systemâ€™s internal energy and the product of its pressure and volume.

Measuring the change in enthalpy allows us to determine whether a reaction was endothermic or exothermic.

**Formula to calculate enthalpy.**

**Example:**

When burning benzoic acid the heat evolved was -768 joules, if it was 1 atm and the volume of the acid was 122 cubic meters, calculate the enthalpy.

Therefore, the enthalpy is -646 J.