Question

# The standard reduction potential for $$Zn^{2+}/ Zn, Ni^{2+}/ Ni$$ and $$Fe^{2+}/ Fe$$ are $$-0.76, 0.23$$ and $$-0.44\ V$$, respectively.The reaction, $$X + Y^{2+} \rightarrow X^{2+} + Y$$ will be spontaneous when

A
X=Ni,Y=Fe
B
X=Ni,Y=Zn
C
X=Fe,Y=Zn
D
X=Zn,Y=Ni

Solution

## The correct option is D $$X = Zn, Y = Ni$$The reaction is spontaneous when $$\triangle G < 0$$ and $$E_{cell}^{\circ} > 0$$.$$\because \triangle G = -nFE^{\circ}$$ and $$E^{\circ} > 0$$Also, $$E^{\circ}_{cell} = E^{\circ}_{oxi} + E^{\circ}_{red}$$ (or) $$E^{\circ}_{cathode} - E^{\circ}_{anode}$$Here, $$E^{\circ}_{cell}$$ for(a) $$-0.67\ V$$, i.e. $$E^{\circ}_{cell} < 0$$     (b) $$-0.99\ V$$, i.e. $$E^{\circ}_{cell} < 0$$(c) $$-0.32\ V$$, i.e. $$E^{\circ}_{cell} < 0$$     (d) $$0.99\ V$$, i.e. $$E^{\circ} > 0$$.Chemistry

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