Enthalpy and Hess’ Law of Constant Heat Summation

Originating from the greek for ‘to warm in’ enthalpy is a thermodynamic potential state function consisting of internal energy plus the product of pressure and volume of the system. Enthalpy is officially measured in joules but antiquated units such as the calorie are still commonly used.

Due to it simplifying the description of energy transfer, enthalpy is often used as an expression of system energy changes in physical, biological, and chemical measurements at a constant pressure. A definite reference point must be used in order to calculate the change in enthalpy of a system as total enthalpy can’t be measured directly.

Lee is a freelance writer with a keen interest in history and science.