Question

Hydrogen overvoltage is observed in:

• A. Oxidation processes
• B. Cathodic processes
• C. Anodic processes
• D. Smelting processes

Hint:

Hydrogen overvoltage occurs during \textbf{hydrogen evolution} at the cathode — it’s the extra voltage needed to overcome slow reaction kinetics on some electrode surfaces.

Answer 1

The Correct Option is B

Step 1: Understanding Hydrogen Overvoltage
Hydrogen overvoltage (or hydrogen overpotential) refers to the extra voltage required beyond the theoretical voltage to produce hydrogen gas at the cathode during electrolysis. This phenomenon arises due to the slow kinetics of the hydrogen evolution reaction on certain electrodes. Step 2: Where Hydrogen Evolution Occurs
Hydrogen gas is liberated at the cathode during electrolysis as per the reaction: \begin{equation} 2H^+ + 2e^- \rightarrow H_2(g) \end{equation} The electrode material and the electrolyte conditions can affect the rate and efficiency of this hydrogen evolution. Due to energy losses, a higher voltage (overvoltage) than theoretically required is needed to drive the reaction. Step 3: Evaluating the Options
- (A) Oxidation processes: These occur at the anode, not relevant to hydrogen evolution.
- (B) Cathodic processes: Correct, as hydrogen gas is released at the cathode during electrolysis.
- (C) Anodic processes: Involve oxidation (e.g., of anions or metal), not H\(_2\) gas evolution.
- (D) Smelting processes: These are metallurgical and thermal processes, unrelated to overvoltage. Conclusion: Hydrogen overvoltage is specifically observed during cathodic processes where hydrogen gas is produced.