How can you measure the enthalpy change per mole of a substance X in a reaction?

Measuring the enthalpy change per mole of a substance in a reaction is most effectively done by recording temperature changes in a calorimeter. This method relies on the principle that when a chemical reaction occurs, energy is either absorbed or released, which results in a change in temperature of the surroundings.

In a calorimetric experiment, the reactants are mixed in the calorimeter, and the resulting temperature change is monitored. By knowing the specific heat capacity of the substance, the mass of the solution, and the temperature change, one can calculate the amount of heat absorbed or released during the reaction. This heat change can be directly correlated to the enthalpy change when normalized for the number of moles of the reactant or product involved in the reaction.

The other methods mentioned, such as measuring gas volume, calculating pH changes, or determining liquid densities, do not provide a direct measure of the enthalpy change. While gas volume measurements can give insights into reaction stoichiometry or shifts in equilibrium, they do not account for the thermal energy changes occurring in the system. pH changes can indicate the progress of a reaction but do not reflect the heat transfer involved. Similarly, the density of liquids does not inform on thermal dynamics of a