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A sample of 0.1 g of water at 100°C and normal pressure (1.013 × 10⁵ Nm⁻²) requires 54 cal of heat energy to convert to steam at 100°C. If the volume of the steam produced is 167.1 cc, the change in internal energy of the sample is,
- 104.3 J
- 208.7 J
- 84.5 J
- 422.2 J
Correct answer: 104.3 J
Solution
The heat energy supplied (Q) is 54 cal = 54 × 4.186 J = 226.04 J. The work done (W) is PΔV = (1.013 × 10⁵) × (167.1 × 10⁻⁶) = 16.93 J. Using the first law of thermodynamics, ΔU = Q - W = 226.04 - 16.93 = 209.11 J. The closest option is 208.7 J.
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