Which of the following statements does NOT apply to Hess's Law?

• A. The enthalpy change of a reaction is independent of the pathway taken.
• B. Hess's Law allows the calculation of enthalpy changes for reactions that cannot be measured directly.
• C. Enthalpy is a state function, so only initial and final states matter.
• D. The total enthalpy change depends on the number of steps in the reaction mechanism.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand Hess's Law, which states that the total enthalpy change for a reaction is the same regardless of the pathway taken, because enthalpy is a state function depending only on initial and final states.
2. Step 2: Recognize that this means the enthalpy change is independent of the number of steps or the mechanism of the reaction; it depends only on the overall change from reactants to products.
3. Step 3: Analyze each statement: the first three statements correctly describe Hess's Law and the nature of enthalpy as a state function.
4. Step 4: Identify that the statement 'The total enthalpy change depends on the number of steps in the reaction mechanism' contradicts Hess's Law, because the enthalpy change does not depend on the number of steps.
5. Step 5: Conclude that the statement about the enthalpy change depending on the number of steps is the one that does NOT apply to Hess's Law.