Konovalov's Rules

two rules expressing the relation-ship between the composition of a liquid solution and the composition and pressure of saturated vapor (or boiling point) in a system comprising two volatile substances. These rules were experimentally and theoretically established by D. P. Konovalov in 1881–84. J. Gibbs derived (1876–78) more general relationships using a different method.

Given identical temperature conditions, the first rule can be expressed as follows: the total saturated vapor pressure of a solution rises with an increase in the concentration of that component whose content is greater in the vapor than in the solution and decreases with an increase in the concentration of that component whose content is lower in the vapor than in the solution.

At identical pressure, this rule may be expressed as follows: the boiling point of a solution rises with an increase in the concentration of that component whose content is lower in the vapor than in the solution and decreases with an increase in the concentration of that component whose content is higher in the vapor than in the solution. A simpler formulation of this rule is used for systems that do not have minimum or maximum points on the total saturated vapor-pressure curve or, consequently, on the boiling-point curve: the saturated vapor of a solution composed of two volatile substances is richer in the component that in the pure state has a higher vapor pressure, that is, a lower boiling point.

The second rule applies to more specific cases. The maximum or minimum points on the total saturated vapor-pressure curve (and correspondingly the minimum or maximum points on the boiling-point curve) correspond to solutions whose composition is the same as that of their saturated vapor.

Konovalov’s rules play an important role in the theory of distillation and rectification processes.