What method is used to find the enthalpy change in a reaction involving substance X?

To determine the enthalpy change in a reaction involving substance X, calculating the energy change per mole of substance X is a key step. This is because enthalpy change (ΔH) is commonly expressed in terms of energy per mole. When you divide the total energy change observed during the reaction by the number of moles of substance X that were involved, you can accurately assess how much energy is associated with each mole of the reactant.

This method allows scientists to compare the enthalpy changes of different reactions by standardizing the results to a per-mole basis, which is essential for understanding reaction energetics and for stoichiometric calculations in varying reaction conditions. Thus, the correct approach to find the enthalpy change is to relate the energy change directly to the amount of substance involved in the reaction, providing a clear understanding of how much energy is released or absorbed in relation to the quantity of material reacted.