Question

Explain why the enthalpy changes for the reaction given are not enthalpies of formation of CaCo3 and HBr:
(a) CaO+CO2--> CaCo3
(b) H2+Br2-->2HBr

Answer 1

Answer:

Enthalpy of formation

The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states. ... For an element: the form in which the element is most stable under 1 bar of pressure.

a) CaCO3

Ca + C(g) + 3/2 O2 = 1CaCO3

b) HBr

1/2 H2 + 1/2Br2 = 1HBr

Thanks for Reading