Thermodynamics

 

 46) (a) H2(g) + Cl2(g) 2HCl (g)

 

             ΔG°rxn = ΣΔGf°(products) - ΣΔGf°(reactants)

             ΔG°rxn = [2ΔGf°(HCl(g))] - [ΔGf°(H2(g)) + ΔGf°(Cl2(g))]

             ΔG°rxn = [2 mol HCl(g) x -95.27 kJ/1 mol HCl(g)] - 0 = -190.54 kJ

             The reaction will be spontaneous at this temperature because the reactants and products are in their standard states and ΔG°rxn < 0.

 

       (b) MgCl2(s) + H2O(l) MgO(s) + 2HCl(g)

 

            ΔG°rxn = ΣΔGf°(products) - ΣΔGf°(reactants)

            ΔG°rxn = [ΔGf°(MgO(s)) + 2ΔGf°(HCl(g))] - [ΔGf°(MgCl2(s)) + ΔGf°(H2O(l))]

            ΔG°rxn = [1 mol MgO(s) x -569.6 kJ/1 mol MgO(s) + 2 mol HCl(g) x -95.27 kJ/1 mol HCl(g)] -

                            [1 mol MgCl2(s) x -592.1 kJ/1 mol MgCl2(s) + 1 mol H2O(l) x -237.13 kJ/1 mol H2O(l)] = +69.1 kJ

            The reaction will be nonspontaneous at this temperature because ΔG°rxn < 0.

 

       (c) 2NH3(g) N2H4(g) + H2(g)

 

            ΔG°rxn = ΣΔGf°(products) - ΣΔGf°(reactants)

            ΔG°rxn = [ΔGf°(N2H4(g)) + 0] - [2ΔGf°(NH3(g)) + 0]

            ΔG°rxn = [1 mol N2H4(g) x 159.4 kJ/1 mol N2H4(g) + 0] - [2 mol NH3(g) x -16.66 kJ/1 mol NH3(g)] = +192.7 kJ

           The reaction will be nonspontaneous at this temperature because ΔG°rxn < 0. 

                            

       (d) 2NOCl(g) 2NO(g) + Cl2(g)

 

            ΔG°rxn = ΣΔGf°(products) - ΣΔGf°(reactants)

            ΔG°rxn = [2ΔGf°(NO(g)) + 0] - [2ΔGf°(NOCl(g))]

            ΔG°rxn = [2 mol NO(g) x 86.71 kJ/1 mol NO(g) + 0] - [2 mol NOCl(g) x 66.3 kJ/1 mol NOCl(g) + 0] = +40.8 kJ

            The reaction will be nonspontaneous at this temperature because ΔG°rxn < 0.