Q. $Cu\ + \ 2HCl\ \rightarrow \ {CuCl}_{2} + \ H_{2}(g)\ \ \ \ \ \ \ \$ $\ \ \ \ \ \ \ \ \ \ \ \ \lbrack E_{{Cu}^{2 +}/Cu}^{{^\circ}}\ = \ + 0.34\ V\ \rbrack$ $Zn\ + \ 2HCl\ \rightarrow \ {ZnCl}_{2} + \ H_{2}(g)\ \ \ \ \ \ \ \$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \lbrack E_{{Zn}^{2 +}/Zn}^{{^\circ}}\ = \ - 0.76\ V\ \rbrack$ $Ag\ + \ 2HCl\ \rightarrow \ AgCl + \ \frac{1}{2}H_{2}(g)\$ $\ \ \ \ \ \ \ \ \ \ \ \ \lbrack E_{{Ag}^{+}/Ag}^{{^\circ}}\ = \ + 0.80\ V\ \rbrack$ Which of the following reaction is feasible ?
A) (ii)
B) (i)
C) (iii)
D) All of these
Explanation
(a)
For a reaction to be feasible, the value of $E_{cell}^{{^\circ}}$ must be positive.
$Cu\ + \ 2HCl\ \rightarrow \ {CuCl}_{2} + \ H_{2}(g)$
$E_{cell}^{{^\circ}} = E_{H^{+}/H_{2}}^{{^\circ}} - E_{{Cu}^{2 +}/Cu}^{{^\circ}}$
= 0.00 – (+0.34) = -0.34 V
$Zn\ + \ 2HCl\ \rightarrow \ {ZnCl}_{2} + \ H_{2}(g)\ \$
$E_{cell}^{{^\circ}} = E_{H^{+}/H_{2}}^{{^\circ}} - E_{{Zn}^{2 +}/Zn}^{{^\circ}}$
= 0.00 – (-0.76) = +0.76 V
$Ag\ + \ 2HCl\ \rightarrow \ AgCl + \ \frac{1}{2}H_{2}(g)\ \ \$
$E_{cell}^{{^\circ}} = E_{H^{+}/H_{2}}^{{^\circ}} - E_{{Ag}^{2 +}/Ag}^{{^\circ}}$
= 0.00 – (0.80) = - 0.80 V
Hence, only reaction (ii) is feasible.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.