Question

16. Does the reaction Cu²⁺ + Mg (s) →    Cu (s) + Mg²⁺ occur spontaneously in aqueous solution?

            A.     yes                      B.    no

17. Does the reaction 2 Al³⁺ + 3 Pb (s) →    2 Al (s) + 3 Pb²⁺ occur spontaneously in aqueous solution?

            A.     yes                      B.    no

Answer 1

Solution :-

The element with lower rediuction potential can reduce the element which have higher reduction potential

following are the reduction potentials for the each element

Cu^2+ +2e- ---- > Cu    Eo = 0.34 V

Mg^2+ +2e- ---- > Mg   Eo= -2.37 V

Al^3+ + 3e- ----- > Al Eo = -1.66 V

Pb^2+ + 2e- ---- > Pb         Eo = -0.13 V

Therefore for the first reaction the Mg is oxidizing and Cu^2+ is reducing

since the Mg have lower reduction potential than the Cu therefore reaction is possible threfore this is the spontaneuos reaction

In the second reaction standard reduction potential of the Al is lower than the Pb

therefore Pb cannot reduce the Al^3+

hence the reaction is non spontaneous

Cu²⁺ + Mg (s) →    Cu (s) + Mg²⁺            Spontaneous

2 Al³⁺ + 3 Pb (s) →    2 Al (s) + 3 Pb²⁺     Non spontaneous