Question

. In the extraction of chlorine from brine _____________.

• A. $E^{\circ }$ for the overall reaction has a positive value
• B. $\Delta G^{\circ }$ for the overall reaction is positive
• C. $\Delta G^{\circ }$ for the overall reaction is negative.
• D. $E^{\circ }$ for the overall reaction has a negative value.

Answer 1

Answer: (B), (D)

$E^{\circ }$ for the overall reaction has a negative value.

Extraction of chlorine from brine.

Chlorine can be manufactured by the electrolysis of a Sodium Chloride solution (brine), which is known as the Chlor Alkali process.

Cathode: $2H^{+}\left(aq\right)+2e^{-}\to H_2\left(g\right)$

Anode: $2C{l}^{-}\left(aq\right)+2e^{-}\to C{l}_2\left(g\right)+2e^{-}$

Overall process: $2NaCl+2H_{2}O\to C{l}_2+H_2+2NaOH$

The Gibbs free energy is related to the poential by $\Delta G^{\circ }$Cell= $-nF{E}^{\circ }$.

Here, $E^{circ}cell<0$, for the electrolytic cell so $\Delta G^{\circ }$ will be positive.

So, this reaction is not a spontaneous reaction and so it requires external emf.

Analysing the options:

In the extraction of chlorine from brine

$\Delta G^{\circ }$^o for the overall reaction is positive.

$E^{\circ }$ for the overall reaction has a negative value.

Hence, the correct options are (B) and (C).