Which of the following best explains why the enthalpy change calculated for a…
CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics
Problem
Which of the following best explains why the enthalpy change calculated for a reaction at constant pressure is based on the amount of the limiting reactant rather than the reactant present in excess?
(a) Because enthalpy is an intensive property, the quantity of excess reactants does not affect its value, so the calculation is referenced to the limiting reactant.
(b) The enthalpy change depends solely on the molar mass of the reactant with the smallest value, which is usually the limiting reactant.
(c) The limiting reactant fixes the maximum extent to which the balanced chemical equation can proceed, so the heat released is directly proportional to its amount.
(d) Excess reactants remain at their standard states throughout the process, so they do not contribute to the overall enthalpy change.