Most liquids follow Trouton's rule, which states that the molar entropy of vaporization lies in the range of 88 ± J/mol-K. The normal boiling points and enthalpies of vaporization of several organic liquids are as follows:
|
Substance
|
Normal Boiling Point (°C)
|
ΔHvap (kJ/mol)
|
|
Acetone, (CH3)2CO
|
56.1
|
29.1
|
|
Dimethyl ether, (CH3)2O
|
-24.8
|
21.5
|
|
Ethanol, C2H5OH
|
78.4
|
38.6
|
|
Octane, C5H18
|
125.6
|
34.4
|
|
Pyridine, C5H5N
|
115.3
|
35.1
|
(a) Calculate ?Svap for each of the liquids. Do all the liquids obey Trouton's rule?
(b) With reference to intermolecular forces, can you explain any exceptions to the rule?
(c) Would you expect water to obey Trouton's rule? By using data in Appendix B, check the accuracy of your conclusion.
(d) Chlorobenzene (C6H5Cl) boils at 131.8 °C. Use Trouton's rule to estimate ?Hvap for this substance.