Page:Text-book of Electrochemistry.djvu/119

 ��VELOCITY OF REACTION.

��CHAP.

��solution of a solid substanlbe is at any moment proportional to the difference between the concentration G when the solution is saturated, and the concentration c at that time i,e, the rate is equal to l^C — c).

The velocity of crystallisation has recently been studied by Tammann (5). The velocity at first increases with the degree of super-cooling, reaches a maximum, then by further depression of the temperature decreases, and may thereafter become very small. H. A. Wilson {G) has shown that the velocity of crystallisation v can be represented by the equation —

��v^K

V

��where 0q — represents the super-cooling, V the viscosity of the liquid, and K a constant.

Influence of Temperature on the Velocity of Reaction. — If we examine the influence of temperature on the specific velocity of a reaction, e,g, the saponification of ethyl acetate, we find that it can be approximately represented by the formula given on page 95 for the change of equilibrium. This is clearly seen from the results given in the following tables, in which are to be found: t, the temperature (Celsius); p (observed), the observed velocity of reaction; and p (calculated), the value calculated according to the formula mentioned: —

��Saponification of Ethyl Acetate.

��t

�p (observed).

�p (calculatec

�o

�(1-92)

�23-G

�(10-92)

�� �