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Question
You are given normal boiling points and standard enthalpies of vapourisation. Calculate the entropy of vapourisation of liquids listed below.
| Liquid | Boiling points (°C) | ΔH (kJ mol−1) |
| Ethanol | 78.4 | + 42.4 |
Solution
Given, Tb = 78.4°C = (78.4 + 273) = 351.4 K
ΔHV(ethanol) = + 42.4 kJ mol−1
∆SV = `(Δ"H"_"V")/"T"_"b"`
∆SV = `(+ 42.4 "kJ mol"^-1)/(351.4 "K")`
∆SV = `(+ 42400 "J mol"^-1)/(351.4 "K")`
∆SV = + 120.66 J K−1 mol−1
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