Question

Standard molar enthalpy of formation, `Delta_(f)H^(c-)` is just a special case of enthalpy of reaction, `Delta_(r)H^(c-)` . Is the `Delta_(r)H^(c-)` for the following reaction same as `Delta_(f)H^(c-)` ? Give reaction for your answer.
`CaO(s) +CO_(2)(g) rarr CaCO_(3)(s), Delta_(f)H^(c-)= - 178. 3 kJ mol^(-1)`

Answer 1

No, because enthalpy of formation is the enthalpy change when 1 mole of the compound is formed from the elements , i.e., for the reaction `Ca(s) + C(s) + (3)/(2) O_(2)(g) rarr CaCO_(3)(s)`. Thus, this reaction is different from the givien reaction. Hence, `Delta_(r) H^(@) cancel(=) Delta_(f)H^(@)`.