1)Fe +S = FeS
Fe(0)-2e=Fe(+2) 1
S(0)+2e=S(-2) 1
Fe(0)+S(0) = Fe(+2) + S(-2)
2)Fe+2HCl = FeCl2 + H2
Fe(0)-2e=Fe(+2) 1
2H(+)+2e=H2(0) 1
Fe(0)+2H(+) = Fe(+2) + H2(0)
Fe + CuSO4 = FeSO4 + Cu
Fe(0)-2e=Fe(+2) 1
Cu(+2)+2e=Cu(0) 1
Fe(0)+Cu(+2) = Fe(+2)+Cu(0)
3Fe+2O2 = Fe3O4