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Q.

You are given normal boiling points and standard enthalpies of vapourisation. Calculate the entropy of vapourisation of liquids listed below. | S.No | Liquid | Boiling point (∘^\circC) | ΔH\Delta H (kJ mol−1^{-1}) | |---|---|---|---| | 1. | Ethanol | 78.4 | +42.4 | | 2. | Toluene | 110.6 | +35.2 |

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Step 1. Entropy of vapourisation: ΔSv=ΔHv/Tb\Delta S_v=\Delta H_v/T_b (eq. 7.33), with TbT_b in kelvin.

Step 2. Ethanol: Tb=78.4+273=351.4T_b=78.4+273=351.4 K, ΔHv=42.4\Delta H_v=42.4 kJ mol−1=42,400^{-1}=42{,}400 J mol−1^{-1}. ΔSv=42,400/351.4≈120.7\Delta S_v=42{,}400/351.4\approx120.7 J K−1^{-1}mol−1^{-1}.

Step 3. Toluene: Tb=110.6+273=383.6T_b=110.6+273=383.6 K, ΔHv=35.2\Delta H_v=35.2 kJ mol−1=35,200^{-1}=35{,}200 J mol−1^{-1}. ΔSv=35,200/383.6≈91.8\Delta S_v=35{,}200/383.6\approx91.8 J K−1^{-1}mol−1^{-1}. …

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