Question

Assertion :The concentration cell $\begin{array}{c}\underset{P_1}{Pt{H}_2}\end{array}\left|\begin{array}{c}HCl\end{array}\right|\begin{array}{c}\underset{P_2}{H_{2}Pt}\end{array}$ would show spontaneous flow of current only when $P_1>P_2$ whereas the concentration cell $\begin{array}{c}Pt{H}_2\end{array}\left|\begin{array}{c}\underset{C_1}{HCl}\end{array}\right|\left|\begin{array}{c}\underset{C_2}{HCl}\end{array}\right|\begin{array}{c}{H}_{2}Pt\end{array}$ show spontaneous flow of current only when $C_2>C_1$. Reason: Case I : $E_{cell}=-\frac{0.059}{2}log\frac{P_2}{P_1}$ Case II : $E_{cell}=-\frac{0.059}{1}log\frac{C_1}{C_2}$

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

For the electrode $\begin{array}{c}\underset{P_1}{Pt{H}_2}\end{array}\left|\begin{array}{c}HCl\end{array}\right|\begin{array}{c}\underset{P_2}{H_{2}Pt}\end{array}$, the electrode reactions are
$H_2\left(P_1\right)\to 2H^{+}+2e$
$2H^{+}+2e\to H_2\left(P_2\right)$
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$H_2\left(P_1\right)\to H_2\left(P_2\right)$

The expression for the cell potential is $E_{cell}=-\frac{0.059}{2}log\frac{P_2}{P_1}$

When $P_1>P_2$, the cell potential is positive and the current flow is spontaneous.

For, the electrode $\begin{array}{c}Pt{H}_2\end{array}\left|\begin{array}{c}\underset{C_1}{HCl}\end{array}\right|\left|\begin{array}{c}\underset{C_2}{HCl}\end{array}\right|\begin{array}{c}{H}_{2}Pt\end{array}$,
$H_2\to 2H^{+}\left(C_1\right)+2e$
$2H_{C_2}^{+}+2e\to H_2$
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$H_{C_2}^{+}\to H_{C_1}^{+}$

The expression for the cll potential is $E_{cell}=-\frac{0.059}{1}log\frac{C_1}{C_2}$

When $C_2>C_1$, the cell potential is positive and the current flow is spontaneous.

Option A is correct.