Question

If enthalpies of formation of CH4(g), CO2(g) and H2O(l) at 25°C and 1 atm pressure are –x, –y and – z kJ/mol respectively, then enthalpy of combustion of CH4 (g) will​

Answer 1

The enthalpy of combustion of CH4 (g) will​ be (x - y - 2z) kJ / mol.

- The combustion of Methane (CH4)  can be shown as :

CH4 (g) + 2 O2 (g) ----> CO2 (g) + 2 H2O (l)

- For this reaction, enthalpy change is given by:

ΔH = ∑ΔH(products) - ∑ΔH(reactants)

⇒ ΔH = {(-y) + 2 (-z)} - {(-x) + (0)}

⇒ ΔH = (x - y - 2z) kJ / mol