LIVING MATTER AND ITS PRODUCTS 149 



P B the osmotic pressure of either of the two substances produced on 

 the right-hand side, for these being produced in equimolecular pro- 

 portion, their osmotic pressures at any given stage in the reaction 

 will be equal in value. 1 



Here, as a result of the reaction, a grm. molecule of A disappears, 



p 

 lowering the volume energy by RT log p-, and a grm. molecule of 



r o 

 each of the two substances formed appears at a pressure P B , raising 



P PB 



the volume energy in each case by RT log p 8 , or in all by 2RT log p"- 



"o r o 



Accordingly our equation becomes 



o 

 or 



As before, the reaction runs exotherniically from either end until 



P 2 

 RT log p -- = C, at which point there is equilibrium. 2 



r A- r o 

 For the heat of reaction at any other point we have 



or, using the same notation as in the other cases, 



or 



v 2 P P 

 H = RTlog PB - . ^ 2 . 



But the zero pressure P and p Q is always the same, hence 



1 If unequal quantities of the two substances formed on the right-hand 

 side are present at the beginning along with the single substance, or a certain 

 amount of one of them, then the osmotic pressures of these two (B and C) 

 will not be equal; but if they are represented by the pressures P B and PC the 

 only difference is that we will have P B .P C in the final equation instead of 



P P 



P B 2 , so that the equation becomes: H = C-RT log p B ' p c , which for equili- 



** -M) 



brium leads to log = or = e^' 



2 As before, the equilibrium equation can accordingly be written 



