Question

What is the Gibbs free energy change, ΔG, for the reaction 2H2(g) + O2(g) → 2H2O(g) at 25°C and 1 bar, given the standard Gibbs free energy of formation values for H2(g), O2(g), and H2O(g)?

Answer 1

To calculate the Gibbs free energy change  G  for the reaction, we need the standard Gibbs free energy of formation  Gf  values for H2 g , O2 g , and H2O g . The standard Gibbs free energy of formation for H2 g  and O2 g  is zero because they are in their elemental form.The standard Gibbs free energy of formation for H2O g  at 25C is -228.57 kJ/mol.Using the stoichiometry of the balanced equation, we can calculate the Gibbs free energy change for the reaction:G =  [Gf products ] -  [Gf reactants ]G = [2  Gf H2O g  ] - [2  Gf H2 g   + Gf O2 g  ]G = [2   -228.57 kJ/mol ] - [2   0 kJ/mol  +  0 kJ/mol ]G = -457.14 kJ/molSo, the Gibbs free energy change  G  for the reaction 2H2 g  + O2 g   2H2O g  at 25C and 1 bar is -457.14 kJ/mol.