Question

Calculate the standard free energy change for the combustion of one mole of methane using the values for standard free energies of formation of the products and reactants. The sign of the standard free energy change allows chemists to predict if the reaction is spontaneous or not under standard conditions and whether it is product-favored or reactant-favored at equilibrium.

_______ kJ/ mol-rxn

Answer 1

combustion reaction of methane is

CH4 (g) + 2 O2 (g) <.....................> CO2 (g) + 2 H2O (l)

thus

ΔG_rxn^o = [ΔG_f^o (products) - ΔG_f^o (reactants)]

or

ΔG_rxn^o = [1*ΔG_f^o (CO2(g)) + 2 *ΔG_f^o (H₂O(l)] – [1*ΔG_f^o CH4 (g)) + 2 * ΔG_f^o (O(2g)]

or

ΔG_rxn^o = [1* (–394.4) + 2 * (–237.1)] – [1 (−74.87)* + 2  ]0.00

or

ΔG_rxn^o = - 793.73 KJ / mole.

As ΔG_rxn^o is negative, so reaction will be spontaneous.

thus

at equilibrium, product-favored.