由下列热力学数据,计算298.15K时Mg2+/Mg电对的标准电极电势。①Mg(s)+1/2O2(g)====MgO(s)=-537kJ·mol-1②MgO(s)+H2O(l)====Mg(OH)2(s)=-31kJ·mol-1③H2(g)+1/2O2(g)====H2O(l)=-241kJ·mol-1④H2O(l)====H++OH-=80kJ·mol-1⑤Mg(OH)2(s)====Mg2+(aq)+2OH-(aq)Ksp=5.5×10-12