heat summation

Hess's law, also known as the law of heat summation, is a principle in chemistry that states the total enthalpy change for a chemical reaction is independent of the pathway taken. This means the amount of heat absorbed or released during a reaction is constant, regardless of the number of steps involved.1

This law is a consequence of the first law of thermodynamics and is crucial for calculating the heat of reactions, especially when direct measurement is impractical. It allows chemists to determine the heat of formation of compounds by combining known heats of formation or combustion for various reaction steps. The heat of reaction, or enthalpy of reaction ((\Delta H)), can be positive (endothermic) or negative (exothermic).123