Question

Consider the following voltaic electrochemical cell reactions of (under standard conditions)

1) Copper (cathode ) and Zinc (anode)

2) Copper (cathode) and Magnesium (anode)

3) Zinc (cathode) and Magnesium (anode)

Of the electrochemical cell reactions listed above (1 - 3) which would be expected to have the smallest K Value? Elaborate.

Answer 1

Cu2+ + 2 e− ⇌ Cu(s) +0.337;

Zn2+ + 2 e− ⇌ Zn(s) −0.7618;

Mg2+ + 2 e− ⇌ Mg(s) −2.372

the lowest value will be tht with the lowest E°cell

dG = -n*F*E°cell

dG = -RT*lnK

RT*lnK = n*F*E°cell

K = exp(n*F/(RT)*E°cell)

E°cell = Ecahtode - EAnode

then, we must find the similar species

those are:

Cu2+ + 2 e− ⇌ Cu(s) +0.337;

Zn2+ + 2 e− ⇌ Zn(s) −0.7618;

E°cell = 0.337 - - 0.7618 = 1.09

all other should have higher values

then

the pair: Copper + Zinc will have the lowest K