What does Hess's Law state?

Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of the number of steps taken to complete the reaction. This principle is based on the fact that enthalpy is a state function, meaning that it depends only on the initial and final states of the system, not on the path taken to get from one to the other. As a result, whether a reaction occurs in one step or multiple steps, the total change in enthalpy remains constant. This law is particularly useful for calculating the enthalpy changes of reactions that may not occur in a single step but can be represented as a series of smaller steps.

Understanding Hess's Law is crucial for thermochemistry as it allows chemists to find the enthalpy changes for complex reactions by using simpler reactions for which the enthalpy values are known.