Raoult's law

noun

Ra·​oult's law rä-ˈülz- 

: a law in physical chemistry: the fraction by which the vapor pressure of a liquid is lowered when a small amount of a substance that is nonvolatile, not capable of being dissociated, and usually not a high polymer is dissolved in it is equal to the ratio of the number of moles of the solute to the total number of moles of all components of the solution