HESS’S LAW

Hess's Law is a fundamental principle in thermochemistry stating that the change in enthalpy (ΔH) of a chemical reaction is independent of the pathway taken, depending only on the initial and final states of the system11. In the context of this laboratory manual, the study of Hess's Law aims to bridge the gap between theoretical thermodynamics and empirical observation2. By measuring the heat of reaction through various experimental routes, students can verify that the total enthalpy change remains constant regardless of whether the reaction occurs in one step or several stages3. The determination of reaction heat is crucial for identifying whether a process is exothermic (releasing heat, ΔH = -) or endothermic (absorbing heat, ΔH = +).