Ncert Exercises & Solutions

Standard molar enthalpy of formation, $∆_{f} H^{⊝}$ is just a special case of enthalpy of reaction, $∆_{r} H^{⊝}$ . Is the $∆_{r} H^{⊝}$ for the following reaction same as $∆_{f} H^{⊝}$ ? Give reason for your answer.

$CaO (s) + {CO}_{2} (g) \to {CaCO}_{3} (s); ∆_{f} H^{⊝} = - 178.3 kJ {mol}^{- 1}$

No, the

∆_{r} H^{⊝}

for the given reaction is not same as

∆_{r} H^{⊝}

. 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,

∆_{f} H^{⊝}

Ca (s) + C (s) + \frac{3}{2} O_{2} (g) \to {CaCO}_{3} (s);

∆_{f} H^{⊝}