One student used bond enthalpy data and correctly calculated the enthalpy change for the reaction between ethanol and ethanoic acid as \( 0~kJ~mol^{-1} \). Another student used enthalpy of formation data and correctly calculated the enthalpy change for the same reaction as \( -4~kJ~mol^{-1} \). \( C_{2}H_{6}O(l)+C_{2}H_{4}O_{2}(l)\rightleftharpoons C_{4}H_{8}O_{2}(l)+H_{2}O(l) \) Explain how the two students can carry out a calculation for the same reaction and obtain different results when both calculations are correct.