Question

If a voltaic cell reaction is written in reverse, the

a. E° becomes positive

b. ∆G° becomes positive

c. reaction becomes spontaneous

d. E° becomes zero

Answer 1

Voltaic cell is a cell which converts chemical energy to electrical energy due to spontaneous chemical reaction.

For a spontaneous chemical reaction, standard electrode potential is positive

ie for a spontaneous reaction, E⁰ is positive.

For example, Zn + Cu²⁺ --------> Cu + Zn^{​​​​​2+} , standard cell potential is + 1.1 V

If the reaction is reversed, the standard cell potential becomes negative of the actual reaction.

if Voltaic cell reaction is reversed, E⁰ becomes negative as it is positive for actual reaction.

Therefore if Voltaic cell reaction is reversed, the reaction becomes non-spontaneous and E° becomes negative.

Since ∆G° and E° are related as

∆G° = -nFE°

If E° is positive, ∆G° becomes negative

If E° is negative, ∆G° becomes positive.

So option B is correct.

Since is E° becomes negative, option A is wrong.

Since the reaction is non spontaneous, option C Is wrong.