Page:Text-book of Electrochemistry.djvu/122

 VII.

��VELOCITY OF REACTION.

��carried out by the gas evolution ; it is the more perfect the greater the mobility of the solution, and, as is well known, this last factor increases with the temperature. A similar reasoning can be applied to other solution processes.

Velocity of Reaction and Osmotic Pressure. — ^It has been shown that in the inversion of cane sugar the quantity of sugar inverted is proportional to its concentration in the solution. This follows firom the agreement between the calculated values and those found by Wilhelmy. However, this connection is only exact because during the reaction invert sugar is formed. If we start with different concentra- tions of cane sugar, we find that for a 40 per cent, solution the velocity constant is more than double that for a 20 per cent, solution. The following table contains the results obtained by Ostwald {11) : —

��Jjrs'^EKSiox OF Cane Suo.ui with 0*5-Normal HCl.

��c

�F

�p

V

�s

�p

B

�40 per cent.

�20 „

�10 „

�4 „

��The table contains under C the number of grams of sugar in 100 c.c. of solution, under p the velocity of reaction, in the third column the ratio of these two, in the fourth column the depression of the freezing point of a solution of the given concentration, and in the last column the ratio between velocity of reaction and the depression of the freezing point. This latter ratio is constant throughout, whilst the quotient

— is entirely dependent on the concentration.

This result can be made clear by a kinetic consideration of the matter. The osmotic pressure at constant temperature is proportional to the number of collisions which the sugar molecules make with the sides of the containing vessel.

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