Approximation formula for chemical equilibria

Approximation Formula for Chemical Equilibria.—We now return to the subject-matter of page 125 instead of operating with the vapour-pressure formula, 

further, as is usually preferable for gaseous systems, we work with partial pressures instead of with concentrations, and put, accordingly, 

The heat evolution, Q, at constant pressure is consequently given by the expression 

In the foregoing formula we have restricted ourselves to the first two terms of the developed series, as was also done in deriving the approximate vapour-pressure formula, 

Conventional Chemical Constants. —The problem now arose to determine the values of C for as many gases as possible we may obviously regard C as a property of the particular gas, because it must be independent of the nature of the condensate, and therefore depends only on the nature of the gas. 

---