For the electrochemical cell M | M2+ || X | X2- If E0(M2+/M) = 0.46 V and E0(X/X2-) = 0.34 V. Which of the following is correct?
- Ecell = 0.80 V
- M + X M2+ + X2- is a spontaneous reaction
- Ecell = -0.80 V
- M2+ + X2- M + X is a spontaneous reaction
Answer
(4) M2+ + X2- M + X is a spontaneous reaction
Solution
Anode: M M2+ + 2e-
Cathode: X + 2e- X2-
E0cell = E0cathode - E0anode = 0.34 - 0.46 = -0.12 V ⇒ (A) and (C) are wrong
(B): E0 = -0.12 V ⇒ G0 = -nFE0 > 0 ⇒ (B) is non-spontaneous
(D): reverse reaction, E0 = 0.12 V ⇒ G0 < 0 ⇒ (D) is spontaneous
Answer: (4)