Enthalpy Reaction from Enthalpy Formation

Question

Using standard heats of formation, calculate the standard enthalpy change for the following reaction.

CaCO₃(s)CaO(s) + CO₂(g)

Answer 1

This type of question is solved by taking the sum of the standard heats of formations of the products minus the sum of standard heats of formation for the reactants. Work is shown below: (kJ/mol)

ΔHf (kJ/mol) CaO(s) = -635.5

ΔHf (kJ/mol) CO₂(g) = -393.5

ΔHf (kJ/mol) CaCO₃(s) = -1207.0 (you use the positive of this number since it is being broken down rather than formed)

[ΔHf (kJ/mol) CaO(s) + ΔHf (kJ/mol) CO₂(g)] - ΔHf (kJ/mol) CaCO₃(s) = standard enthalpy change

[(-635.5)+(-393.50] - 1207.0 = -178 kJ/mol