Key idea: Enthalpy is a state function

The enthalpy change of a reaction, $\Delta H$, depends only on the initial state and the final state of the system, not on the path by which the reaction occurs.

This is the basis of Hess's law.

$\Delta H = H_{\text{products}} - H_{\text{reactants}}$

Interpret the question

We need the factor on which enthalpy change does not depend.

Check each option

A: use of different reactants for the same product

If different reactants are used to form the same product, then the initial state changes. Since $\Delta H$ depends on initial and final states, it can change.

So, $\Delta H$ does depend on this.

A is incorrect.

B: the nature of intermediate reaction steps

Since enthalpy is a state function, the route or mechanism of the reaction does not matter.

Whether the reaction occurs in one step or many steps, total enthalpy change remains the same.

$\Delta H_{\text{overall}} = \text{same regardless of intermediate steps}$

So, $\Delta H$ does not depend on intermediate steps.

B is correct.

C: the differences in initial or final temperature of involved substances

Enthalpy change depends on the temperature at which reactants and products are considered. Changing temperature changes enthalpy values.

So, $\Delta H$ does depend on temperature.

C is incorrect.

D: the physical states of reactants and products

Enthalpy depends on physical state, e.g.,

• $\mathrm{H_2O(l)}$
• $\mathrm{H_2O(g)}$

Since these have different enthalpies, reaction enthalpy changes if physical states change.

So, $\Delta H$ does depend on physical states.

D is incorrect.

Final answer

The enthalpy change for a reaction does not depend upon:

$\boxed{\text{B: the nature of intermediate reaction steps}}$

Comparison with stored answer

Stored correct answer: B

Derived answer: B

They match.