What does Hess's Law state about enthalpy change in chemical reactions?

Hess's Law establishes that the total enthalpy change for a chemical reaction is constant, regardless of the number of steps involved in the reaction or the specific pathway taken to achieve that change. This principle is grounded in the first law of thermodynamics, which asserts that energy cannot be created or destroyed, only transformed.

When considering a reaction that can occur through multiple pathways, Hess's Law allows chemists to calculate the enthalpy change of the overall reaction by summing the enthalpy changes of individual steps, regardless of whether those steps are hypothetical or actual. This is particularly useful because it means that if you know the enthalpy changes for several individual reactions that add up to your overall reaction, you can add those values to find the total enthalpy change.

This principle facilitates the calculation of enthalpy changes for reactions that might be difficult to measure directly. It emphasizes the relationship between the final and initial states of a system rather than the specifics of the transformation, reinforcing that enthalpy is a state function.

The other options presented do not accurately represent the core tenet of Hess's Law. For example, the speed of the reaction (kinetics) and the nature of the pathways are irrelevant to the enthalpy