For which of the following reactions is ΔH∘rxn equal to ΔH∘f of the product (s) ?

Choose all that apply.

a. C (s, graphite) + O2 (g) →CO2 (g)

b. Li (s) + 12Cl2 (g) →LiCl (s)

c. Li (s) + 12Cl2 (l) →LiCl (s)

d. 2Li (s) + Cl2 (g) →2LiCl (s)

e. CO (g) + 12O2 (g) →CO2 (g)

f. BaCO3 (s) →BaO (s) + CO2 (g)

The correct answers are A, B, and D. The ΔHrxn is equal to the ΔHf when the ΔHf of the reactants is zero, and this can only occur when the reactants are pure elements (not compounds) in their natural phase at ambient temperature.

c) Chlorine's natural phase is gaseous, but since it is a liquid in this reaction, ΔHf ≠ 0.

e) CO is a compound, not a pure element.

f) BaCO3 is a compound, not a pure element.