The standard Gibbs energy for the given cell reaction in $kJ \, mol^{-1}$ at $298 \, K$ is $Zn_{(s)} + Cu^{2+}_{(aq)} \to Zn^{2+}_{(aq)} + Cu_{(s)}$,given $E^o = 2 \, V$ at $298 \, K$ [Faraday's constant $F = 96500 \, C \, mol^{-1}$].

If standard reduction potential $(E^{\circ})$ of $(Ni_{(aq)}^{+2} \mid Ni_{(s)})$ and $(Al_{(aq)}^{+3} \mid Al_{(s)})$ are $-0.25 \ V$ and $-1.66 \ V$ respectively,what is the standard emf of the cell reaction $2 \ Al_{(s)} + 3 \ Ni_{(aq)}^{+2} \rightarrow 2 \ Al_{(aq)}^{+3} + 3 \ Ni_{(s)}$?

For the reactions $Ag^{+} (aq) + e^{-} \rightarrow Ag_{(s)}$ and $Sn^{2+} (aq) + 2e^{-} \rightarrow Sn_{(s)}$,the standard electrode potentials at $25^{\circ}C$ are $0.80 \ V$ and $-0.14 \ V$ respectively. What is the standard $emf$ of the cell $Sn_{(s)} | Sn^{2+}_{(aq)} (1 \ M) || Ag^{+}_{(aq)} (1 \ M) | Ag_{(s)}$ in $volts$?

The e.m.f. of a cell whose half cells are given below is .............. $V$
$Mg^{2+} + 2e^- \to Mg_{(s)}$; $E^o = - 2.37 \ V$
$Cu^{2+} + 2e^- \to Cu_{(s)}$; $E^o = + 0.34 \ V$

$E^o$ values for the half-cell reactions are given below:
$Cu^{2+} + e^- \to Cu^{+} \quad E^o = 0.15 \ V$
$Cu^{2+} + 2e^- \to Cu \quad E^o = 0.34 \ V$
What will be the $E^o$ for the half-cell reaction:
$Cu^{+} + e^- \to Cu$ ? $\dots \ V$

When does a cell reaction occur spontaneously?