9+ GENERAL CONDITIONS OF EQUILIBRIUM, chap.

where /x denotes the heat absorbed when a gram-molecule of ammonium chloride is transformed into a mol of ammonia and a mol of hydrochloric acid. The condition for the applicability of this equation is that the pressure remains constant ; if the change takes place at constant volume, then, as in the case of solutions, we may introduce the concentra- tions (C) instead of the pressures, and obtain —

d(ln Ci + In C;^^ In Ci) ^ _^ (IT ~ BT^'

a In —7-7 —

or - a — /*

��(IT BT^

We know that at constant temperature —

��a

��or integrated —

��We therefore have for the change of K with change of temperature —

(IT BT^'

where M is a constant, or finally —

In general, for a reaction which takes place according to the chemical equation —

mP + nQ + oB + , . . =. fS -k- gT + hV + . . . we have the equilibrium equation —

v a n .s r r

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