Question

$Z{n}^{2+}\to Z{n}_{(s)};E^{°}=-0.76V$
$C{u}^{2+}\to C{u}_{(s)};E^{°}=-0.34V$
Which of the following is spontaneous?

• A. $Z{n}^{2+}+Cu\to Zn+C{u}^{2+}$
• B. $C{u}^{2+}+Zn\to Cu+Z{n}^{2+}$
• C. $Z{n}^{2+}+C{u}^{2+}\to Zn+Cu$
• D. none of these

Answer 1

Answer: (B)

$z{n}^{2+}\to Z{n}_s;E^{\circ }=-0.76V$
$C{u}^{2+}\to C{u}_{\left(s\right)};E^{\circ }=-0.34V$
A redox reaction is feasible if $E_{cell}$ is Positive.
$\frac{\begin{array}{c}z{n}^{2+}+2e^{-}\to Z{n}_{\left(s\right)};E^{\circ }=-0.76V\\ C{u}^{2+}+2e^{-}\to C{u}_{\left(s\right)};E^{\circ }=-0.34V\end{array}}{\therefore C{u}^{2+}+zn\to z{n}^{2+}+Cu;}$
$E_{cell}=E_{\left(C{u}^{2+}/cu\right)}^{\circ }-E_{\left(z{n}^{2+}/zn\right)}^{\circ }$
Therefore, $E_{cell}=-0.34-\left(-0.76\right)$
$=-0.34+0.76=+0.42V$