2Cu+O2=2CuO Cu(0)-2e=Cu(+2) O2+4e=2O(-2) CuO=Cu+O2 Cu(+2)+2e=Cu(0) 2O(-2) -4e O2(0) 2H2O=2H2+O2 2H(+1)+2e=H2(0) 2O(-2)+4e=O2(0) 4Al+3O2=2Al2O3 Al(0)-3e=Al(+3) O2(0)+4e=2O(-2)