CHEMICAL THEORY OF SOLUTIONS. PART I. 59 



Thus we see that the state of homogeneous equilibrium at 

 a constant temperature in a system consisting of an associated 

 and a normal component and in wliicli the reversible reaction 



takes place, can be completely represented by a diagram like 

 that shown in Fig. 12. 



{b) The Equlibrium between a Gaseous and a 

 Liquid Phase. 



(1) Vapour Pressure at a Constant Température. 



Let ^\, ^^ß, and p be the partial pressures of 'S«, ©p, and 

 © respectively in the gas pliase which is in equilibrium with 

 the solution consisting of these chemical species, and let P be the 

 vapour tension of the pure ©. Then we have by equation (5) 



and 



P=C,7:,+ C^7:r,+ CP„ (44) 



where P is the total pressure. 



The curves representing the relation between these partial 

 pressures and the empirical molar fractions must have forms 

 resembling those given in Fig. 12. As a rule -^ will be far 

 larger than -p, so that the curve for ^j^ will often lie far below 

 that for 2:>^. 



When these curves of partial pressures are given, we can 



