Trouton's rule

Trouton’s rule states that the entropy of vaporization is almost the same value, about 87–88 J K⁻¹ mol⁻¹, for various kinds of liquids. The entropy of vaporization is defined as the ratio between the enthalpy of vaporization and the boiling temperature. It is named after Frederick Thomas Trouton.

Mathematically, it can be expressed as:

Failed to parse (unknown function "\rise"): {\displaystyle \rise to a large rotational constant (B), with correspondingly widely separated rotational energy levels and, via Maxwell-Boltzmann distribution, a small population of excited rotational states and hence a low rotational entropy. Trouton's rule validity can be increased by considering: :<math>\Delta \bar S_{vap} = 4.5R + R\ln T}

Here, if T = 400 K, we find the original formulation for Trouton's rule.

Another equation which T_boiling < 2100 K is ΔH_boiling = 87 T_boiling − 0.4 J/K.

Further reading

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