To calculate the Gibbs free energy change G for the reaction, we can use the following equation:G = Gf products - Gf reactants where Gf represents the standard Gibbs free energy of formation of the respective compounds.For the given reaction:2NO g + O2 g 2NO2 g G = [2 Gf NO2 ] - [2 Gf NO + Gf O2 ]We are given the standard Gibbs free energy of formation for NO, O2, and NO2 as +90.4 kJ/mol, 0 kJ/mol, and +51.3 kJ/mol, respectively.Substitute the given values into the equation:G = [2 +51.3 kJ/mol ] - [2 +90.4 kJ/mol + 0 kJ/mol]G = [102.6 kJ/mol] - [180.8 kJ/mol]G = -78.2 kJ/molThe Gibbs free energy change at 25C for the reaction is -78.2 kJ/mol.