Page:Outlines of Physical Chemistry - 1899.djvu/252

 284 OUTLINES OF PHYSICAL CHEMISTRY

portions, this ratio remains constant, and by means of it the value of x can be calculated from the equation

h (a — x) (b — x) = k x (a x + x) {b Y + x).

Knowing thus the division of the base between the acids we can calculate the accompanying thermal effect and confirm theory by experiment. Thomsen has found :

Equivalents mixed Thermal effect

(a) (6) (a,) (&!> Calculated Observed

i 1 — — -1-331 OaL -1-292 Gal

1 1 — - -1-773 „ -1-752 „

2 1 — — -1-974 „ -2026 „ 2 1 1 — -0-982 „ -0-978 „

— — 1 1 +0-298 „ +0-288 „

— — 2 1 +0-348 „ +0-379 „

There is no doubt about the conclusion — Guldberg and Waage's theory is in this case also supported by facts. If we return now to the simplest case

��we see that

��(a = b = 1, a x = b x = 0),

��V F =

���X

The ratio ~ tells us how many times x (the quan-

x "■ x

tity of nitric acid which is transformed to nitrate) is greater than 1 — x (the quantity of remaining sulphate). This ratio is termed the avidity, and expresses, according to Thomsen, the relative energy with which the acids tend to seize their part of the base. 1 The following table gives the relative avidity for a number of acids compared with nitric acid as standard : —

1 The equation of equilibrium contains the active mass of the

k acid and also that of the base ; that is the reason why the ratio =- is

equal to the square of the avidity. This is confirmed by other func- tions which we shall study later.

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