Question

The standard reduction potential for $Z{n}^{2+}/Zn,N{i}^{2+}/Ni$ and $F{e}^{2+}/Fe$ are $-0.76,0.23$ and $-0.44V$, respectively.

The reaction, $X+Y^{2+}\to X^{2+}+Y$ will be spontaneous when

• A. $X=Ni,Y=Fe$
• B. $X=Ni,Y=Zn$
• C. $X=Fe,Y=Zn$
• D. $X=Zn,Y=Ni$

Answer 1

The correct option is D $X=Zn,Y=Ni$

The reaction is spontaneous when $△G<0$ and $E_{cell}^{\circ }>0$.

$\because △G=-nF{E}^{\circ }$ and $E^{\circ }>0$

Also, $E_{cell}^{\circ }=E_{oxi}^{\circ }+E_{red}^{\circ }$ (or) $E_{cathode}^{\circ }-E_{anode}^{\circ }$

Here, $E_{cell}^{\circ }$ for

(a) $-0.67V$, i.e. $E_{cell}^{\circ }<0$ (b) $-0.99V$, i.e. $E_{cell}^{\circ }<0$

(c) $-0.32V$, i.e. $E_{cell}^{\circ }<0$ (d) $0.99V$, i.e. $E^{\circ }>0$.