liquids can be expected to have sim

liquids can be expected to have similar standard entropies of vaporization. Liquids
that show significant deviations from Trouton’s rule do so on account of strong
molecular interactions that result in a partial ordering of their molecules. As a result,
there is a greater change in disorder when the liquid turns into a vapour than for a
fully disordered liquid. An example is water, where the large entropy of vaporization
reflects the presence of structure arising from hydrogen-bonding in the liquid.
Hydrogen bonds tend to organize the molecules in the liquid so that they are less random
than, for example, the molecules in liquid hydrogen sulfide (in which there is no
hydrogen bonding). Methane has an unusually low entropy of vaporization. A part of
the reason is that the entropy of the gas itself is slightly low (186 J K−1 mol−1 at 298 K);
the entropy of N2 under the same conditions is 192 J K−1 mol−1
. As we shall see in
Chapter 12, fewer rotational states are accessible at room temperature for light
molecules than for heavy molecules