Question

The reduction potential of hydrogen half-cell will be negative if

• A. $p\left(H_{2}\right)=1\, atm$ and $\left[H^{+}\right]=1.0\, M$
• B. $p\left(H_{2}\right)=1 \,atm$ and $\left[H^{+}\right]=2.0 \,M$
• C. $p\left(H_{2}\right)=2 \,atm$ and $\left[H^{+}\right]=1.0 \,M$
• D. $p\left(H_{2}\right)=2 \,atm$ and $\left[H^{+}\right]=2.0\, M$

Answer 1

Answer: (C)

Reaction $2 H ^{+}+2 e \rightarrow H _{2}$
$\therefore n=2, \,\, Q =\frac{P_{H_{2}}}{\left[H^{+}\right]^{2}} $
As $E_{H^{-} / H_{2}} =E_{H^{-} / H_{2}}^{\circ} \frac{-0.059}{n} \log Q$
$=-\frac{0.059}{2} \log Q $
$\therefore $ if $Q > 1 E_{H^{-} / H_{2}} < 0$

A	$Q = \frac{1}{1} = 1$	X
B	$Q = \frac{1}{2^2} < 1$	X
C	$Q = \frac{2}{12} > 1$	$\checkmark$
D	$Q = \frac{2}{2^2} < 1$	X