Question

The complete combustion of cyclohexane occurs according to the following equation:

C₆H₁₂(g) + 9O₂(g) → 6CO₂(g) + 6H₂O(l)

For this process, Δ_combH^o(298 K) = -3952 kJ mol^-1. If values of Δ_fH^o(298 K) for CO₂(g) and H₂O(l) are -394 and -286 kJ mol^-1, respectively, what is the value of Δ_fH^o(C₆H₁₂, g, 298K)?

Answer 1

we have:

deltaHo rxn = -3952.0 KJ/mol

Hof(O2(g)) = 0.0 KJ/mol

Hof(CO2(g)) = -394.0 KJ/mol

Hof(H2O(l)) = -286.0 KJ/mol

we have the Balanced chemical equation as:

C6H12(g) + 9 O2(g) ---> 6 CO2(g) + 6 H2O(l)

deltaHo rxn = 6*Hof(CO2(g)) + 6*Hof(H2O(l)) - 1*Hof( C6H12(g)) - 9*Hof(O2(g))

-3952.0 = 6*(-394.0) + 6*(-286.0) - 1*Hof(C6H12(g)) - 9*(0.0)

Hof(C6H12(g)) = -128 KJ/mol

Answer: -128 KJ/mol