Question

Standard electrode potentials are
Fe2+/Fe; E° = -0.44 volts
Fe3+/Fe2+; E° = 0.77 volts
Fe2+, Fe3+ and Fe blocks are kept together, then
(1) Fe3+ increases
(2) Fe3+ decreases
(3) Fe2+/Fe3+ remains unchanged
(4) Fe2+ decreases​

Answer 1

If Fe2+, Fe3+ and Fe blocks are kept together then Fe3+ decrease.

• In case of standard electrode potential,

1. positive value indicates a spontaneous reaction.
2. negative value indicates a non-spontaneous reaction.
3. No value (=0) means no change.

• This is just the opposite of Gibb's free energy change, where positive value indicates non-spontaneous reaction and negative value represents the spontaneous reaction.
• According to the question, the positive value is Fe3+/Fe2+ so Fe3+ will spontaneously convert to Fe2+.
• Hence, Fe2+ will increase and Fe3+ will decrease.