enthalpy change for 2 C(s) + 3H2(g) → C2H6(g) using hess law and reactions 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l), C(s) + O2(g) → CO2(g) and 2 H2(g) + O2(g) → 2H2O(l)