The van't Hoff-Raoult Formula

Wilder D. Bancroft
1905 The Journal of Physical Chemistry  
By means of a thermodynamical cycle involving the use of a semipermeable piston, van't Hoff deduced in 1885 an equation' which can be written in the forni In this equation P is the osmotic pressure, V the volume through which the piston moves in squeezing out the amount of solvent in which one molecular weight of the solute is dissolved, R is the gas constant, ' I ' is the absolute temperature, ?z is the grams of solute divided by the molecular weight of the solute in the solution, N is the
more » ... ution, N is the grams of solvent per molecular weight of solute divided by the molecular weight of the solvent when in the form of vapor, Po is the vapor-pressure of the pure solvent at the temperature T, while p1 is the partial pressure of the solvent in the solution a t the same temperature. In deducing this equation the assumptions were made that the vapor of the solvent followed the gas law and that the volume of the liquid could be neglected in comparison with that of the vapor when calculating the work done in an isothermal distillation. Xo other assumption is involved and the formula must be absolutely accurate except in so far as corrections due to the two explicit assumptions have to be made. The value of these corrections is easily determined in any particular case. It is to be noticed that the volume V is not the molecular volume of the solution except for solutions2 so dilute " t h a t the volume occupied by the molecules of the solute is negligible in comparison with the volume of the solution." _ _ _ _ _~. _ _ Kongl-Sveiiska Vetenikaps-..lkademieiis Handlingar, 21, 3 (18S6) ; van't Hoff: Zeit. phys Clieni , I, 483 (1857). Zeit. phys. Chein., I, 481 (IUS~.)
doi:10.1021/j150077a001 fatcat:kcjjwo3ojfbvlltwma6wp3yt2m