Question

When 1 g hydrogen (ECE = \(1.044 \times 10^{-8} \, \text{kg C}^{-1}\)) forms water, 34 kcal heat is liberated. The minimum voltage required to decompose water is :

• A. 0.75 V
• B. 3 V
• C. 1.5 V
• D. 4.5 V

Hint:

Use \(E = VQ\) and electrochemical equivalent relation to connect energy and charge.

Answer 1

The Correct Option is C

Concept: Energy required: \[ E = VQ \]

Step 1: Convert heat.
\[ Q_{heat} = 34 \times 10^3 \, \text{cal} = 34 \times 10^3 \times 4.2 = 1.428 \times 10^5 \, J \]

Step 2: Charge required.
\[ Q = \frac{m}{Z} = \frac{10^{-3}}{1.044 \times 10^{-8}} = 9.58 \times 10^4 \, C \]

Step 3: Voltage.
\[ V = \frac{E}{Q} = \frac{1.428 \times 10^5}{9.58 \times 10^4} = 1.5 \, V \]