Enthalpy change for a reaction does not depend upon:

Introduction:
Enthalpy change, often represented as ΔH, is a measure of the heat energy exchanged during a chemical reaction. It indicates whether a reaction is exothermic (releasing heat) or endothermic (absorbing heat). The enthalpy change for a reaction is independent of certain factors, as discussed below.

Physical states of reactants and products:
The enthalpy change for a reaction is calculated based on the molar quantities of reactants and products, regardless of their physical states. Whether the reactants and products are in the gas, liquid, or solid state, the enthalpy change remains the same. This is because the enthalpy change is related to the chemical bonds broken and formed, not the physical arrangement of the molecules.

Use of different reactants for the same product:
The enthalpy change for a reaction is determined by the specific chemical equation and the stoichiometry of the reaction. It does not depend on the specific reactants used to produce the same product. As long as the balanced chemical equation remains the same, the enthalpy change will be constant. For example, the combustion of methane and the combustion of ethane both produce carbon dioxide and water, and the enthalpy change for these reactions will be the same.

The nature of the intermediate reaction steps:
The enthalpy change for a reaction is a state function, which means it depends only on the initial and final states of the system, not on the path taken. The intermediate reaction steps or mechanisms that occur during a reaction do not affect the overall enthalpy change. The enthalpy change is determined by the difference in the potential energy of the reactants and products, regardless of the specific steps involved in the reaction.

Differences in initial or final temperature of involved substances:
The enthalpy change for a reaction is not influenced by the initial or final temperatures of the substances involved. The enthalpy change is solely dependent on the energy difference between the reactants and products, not on the temperature at which the reaction occurs. However, the temperature can affect the rate of reaction, but it does not have a direct impact on the enthalpy change.

Conclusion:
The enthalpy change for a reaction is independent of the physical states of reactants and products, the specific reactants used, the nature of the intermediate reaction steps, and the differences in initial or final temperature. These factors do not affect the overall enthalpy change, which is determined solely by the difference in potential energy between the reactants and products.