Standard molar enthalpy of formation, fH is just a special case of enthalpy of reaction, rH. Is the rH for the following reaction same as fH? Give reason for your answer.

CaO(s)+CO2(g)CaCO3(s); fH=-178.3 kJ mol-1


No, the rH for the given reaction is not same as rH. The standard enthalpy change for the formation of one mole of a compound from its elements in their most stable states (reference states) is called standard molar enthalpy of formation, fH.
Ca(s)+C(s)+32O2(g)CaCO3(s); fH