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Entropy
Appears in
Concepts tested here
- Entropy of fusion
- Entropy of vaporisation
All Questions
2012 AIPMT-PRE 1 question
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The enthalpy of fusion of water is 1.435 kcal/mol. The molar entropy change for the melting of ice at $0^\circ C$ isAt the melting point the process is reversible, so $\Delta S_{fusion} = \frac{\Delta H_f}{T}$
$\Delta H_f = 1.435$ kcal/mol $= 1.435\times10^3$ cal/mol; T = 273 K
$\Delta S_{fusion} = \frac{1.435\times10^3}{273} = 5.26$ cal/(mol K)
2011 AIPMT-PRE 1 question
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If the enthalpy change for the transition of liquid water to steam is 30 kJ $mol^{-1}$ at $27^\circ C$, the entropy change for the process would beFor a phase transition at equilibrium, $\Delta S = \frac{\Delta H}{T}$
$\Delta H_{vap} = 30$ kJ $mol^{-1}$ = 30000 J $mol^{-1}$
T = 27 + 273 = 300 K
$\Delta S_{vap} = \frac{30000}{300}$
$\Delta S_{vap} = 100$ J $mol^{-1}K^{-1}$