Question

The half-cell reaction for the SHE is given by

• A. \(2H^+(aq)+2e^- \rightleftharpoons 2H_2(g)\)
• B. \(2H^+(aq)+2e^- \rightleftharpoons H_2(g)\)
• C. \(H^+(aq)+e^- \rightleftharpoons H_2(g)\)
• D. \(Hg_2^{2+}(aq)+2e^- \rightleftharpoons 2Hg(l)\)

Hint:

Standard hydrogen electrode reaction: \[ 2H^+(aq)+2e^- \rightleftharpoons H_2(g) \] Its standard electrode potential is \(0.00\ \text{V}\).

Answer 1

The Correct Option is B

Concept:
SHE stands for Standard Hydrogen Electrode. It is used as a reference electrode. Its electrode potential is taken as: \[ E^\circ=0.00\ \text{V} \] The electrode consists of hydrogen gas at 1 atm pressure passed over platinum electrode dipped in \(1M\) \(H^+\) solution.

Step 1: Understand the reaction at SHE.
At the hydrogen electrode, hydrogen ions can gain electrons and form hydrogen gas. The reduction half-cell reaction is: \[ 2H^+(aq)+2e^- \rightarrow H_2(g) \] Since electrode reactions are reversible, it is written as: \[ 2H^+(aq)+2e^- \rightleftharpoons H_2(g) \]

Step 2: Check balancing of atoms and charge.
Left side: \[ 2H^+ +2e^- \] Total charge: \[ +2-2=0 \] Right side: \[ H_2 \] Charge: \[ 0 \] So the reaction is balanced.

Step 3: Check the options.
Option (A) is incorrect because it forms \(2H_2\), which is not balanced with \(2H^+\).
Option (B) is correct.
Option (C) is incorrect because one \(H^+\) and one electron cannot form \(H_2\).
Option (D) is a mercury electrode reaction, not SHE. Hence, the correct answer is: \[ \boxed{(B)\ 2H^+(aq)+2e^- \rightleftharpoons H_2(g)} \]