To calculate the Gibbs free energy change G for the reaction, we can use the following equation:G = H - TSwhere 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 substances involved in the reaction.Standard enthalpies of formation Hf at 298 K:H2 g = 0 kJ/mol since it is an element in its standard state O2 g = 0 kJ/mol since it is an element in its standard state H2O g = -241.8 kJ/molStandard entropies S at 298 K:H2 g = 130.7 J/molKO2 g = 205.2 J/molKH2O g = 188.8 J/molKNow, we can calculate the standard enthalpy change H and standard entropy change S for the reaction:H = [2 -241.8 kJ/mol ] - [2 0 kJ/mol + 0 kJ/mol] = -483.6 kJ/molS = [2 188.8 J/molK ] - [2 130.7 J/molK + 205.2 J/molK] = 101.6 J/molKNow, we can calculate the Gibbs free energy change G at 298 K:G = H - TS = -483.6 kJ/mol - 298 K 101.6 J/molK 1 kJ/1000 J -457.3 kJ/molSo, the Gibbs free energy change for the reaction at standard conditions 298 K and 1 atm pressure is approximately -457.3 kJ/mol.