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Calculate the total entropy change when 1 kg of ice at 273 K is completely converted to water vapour at 383 K. Use: specific heat of liquid water = 4.2 kJ K⁻¹ kg⁻¹, specific heat of water vapour = 2.0 kJ K⁻¹ kg⁻¹, latent heat of fusion = 344 kJ kg⁻¹, latent heat of vaporisation = 2491 kJ kg⁻¹. (log 273 = 2.436, log 373 = 2.572, log 383 = 2.583)

1. 7.90 kJ kg⁻¹ K⁻¹
2. 2.64 kJ kg⁻¹ K⁻¹
3. 8.49 kJ kg⁻¹ K⁻¹
4. 9.31 kJ kg⁻¹ K⁻¹

Correct answer: 8.49 kJ kg⁻¹ K⁻¹

Solution

The total entropy change is the sum of four contributions: isothermal melting, isobaric heating of liquid water, isothermal vaporisation, and isobaric heating of steam. Each stage's entropy change is calculated separately and added.

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