Final answer:
Enthalpy change is a state function that depends only on initial and final states, not on the reaction pathway. This principle underlies Hess's law, which states that the enthalpy change for a total reaction is the sum of the changes for individual reaction steps.
Step-by-step explanation:
Enthalpy change is considered a state function because it is determined solely by the initial and final states of a process, irrespective of the path taken to get from one state to the other. This is analogous to how the altitude change in climbing a mountain is the same no matter the path taken; it depends only on the starting and ending points. Consequently, Hess's law takes advantage of this property of enthalpy. Hess's law states that the total enthalpy change for a reaction is equal to the sum of enthalpy changes for individual steps comprising the overall reaction process. Therefore, enthalpy changes of intermediate reactions in a multi-step process can be combined to determine the enthalpy change of the overall reaction, regardless of whether the reaction actually proceeds through those intermediate steps.