Question

Calculate the Gibbs free energy change (∆G) for the combustion of methane, CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l), at standard conditions (298 K and 1 atm pressure) using appropriate thermodynamic data.

Answer 1

To calculate the Gibbs free energy change  G  for the combustion of methane at standard conditions, we need to use the following equation:G = H - TSwhere G is the change in Gibbs free energy, H is the change in enthalpy, T is the temperature in Kelvin, and S is the change in entropy.First, we need to find the standard enthalpy change  H  and standard entropy change  S  for the reaction. We can do this by using the standard enthalpies of formation and standard entropies of the reactants and products.Standard enthalpies of formation  Hf  at 298 K  in kJ/mol :CH4 g : -74.8O2 g : 0  element in its standard state CO2 g : -393.5H2O l : -285.8Standard entropies  S  at 298 K  in J/molK :CH4 g : 186.3O2 g : 205.1CO2 g : 213.8H2O l : 69.9Now, we can calculate the standard enthalpy change  H  and standard entropy change  S  for the reaction:H = [1   -393.5  + 2   -285.8 ] - [1   -74.8  + 2  0] = -890.9 kJ/molS = [ 1  213.8 + 2  69.9  -  1  186.3 + 2  205.1 ] = -164.2 J/molKNow, we can calculate the Gibbs free energy change  G  at 298 K:G = H - TS = -890.9 kJ/mol -  298 K  -164.2 J/molK  1 kJ/1000 J  = -802.3 kJ/molSo, the Gibbs free energy change  G  for the combustion of methane at standard conditions is -802.3 kJ/mol.