Page:Outlines of Physical Chemistry - 1899.djvu/259

 the temperature is higher, that is to say, a lower propor- tion will counterbalance the action of the vapour if the temperature is higher. These facts are expressed in the equation

k * (a — x) = k x ttj (a l + x),

in which w and ir x are the constant active masses, a and a x the initial masses of the gaseous products.

A similar example has been studied by Quldberg and Waage — namely, the reversible reaction

BaS0 4 + K 2 C0 3 ^ K 2 S0 4 + BaC0 3.

As the theory predicts, it has been found that the

equilibrium requires a constant ratio (4 : 1) between the

active masses of the soluble substances K 2 C0 3 and K 2 S0 4.

(See also Nernst, * Theoretische Chemie," 1898, p. 498.)

��B. Dissociation Phenomena

When a substance is decomposed by heat, giving one or more volatile products, similar equilibria are observed to those which obtain in the case of reversible reactions.

Calcvum carbonate, for example, commences to decom- pose about 450°0. into lime and carbon dioxide. To each degree of temperature there corresponds a dissociation pressure, that is, a certain concentration of the gaseous product. According to Guldberg and Waage's theory, equilibrium will be established when

/Or = k X TTj u.

In this equation k and k x have their usual signification (and are functions of the temperature), n and 7r, denote the constant active masses of the undecomposed carbonate and of the lime formed, and u is the variable concentration (pressure) of the evolved carbon dioxide. The only

B

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