Laboratory manual of biological chemistry : with supplement / by Otto Folin.

  • Folin, Otto, 1867-1934.
Date:
[1934], ©1934
Catalogue details

Licence: Public Domain Mark

Credit: Laboratory manual of biological chemistry : with supplement / by Otto Folin. Source: Wellcome Collection.

    25/388 (page 11)
    not only of pure water, but of any neutral aqueous solution. On the other hand, a solution is acid if its [H'J is greater than its [OH], and alkaline if the reverse is the case. The nature of the equilibrium between water and its two ions can be shown by means of the Law of Mass Action. Law of Mass Action.—If two substances, A and B, when brought together in solution, react with each other to form two other substances, C and D, and if these two can react with each other in such a way that they are converted back into A and B, the reaction is a reversible one, and can be expressed as follows: A + B^±C+D The two opposing reactions concerned may be called Reaction i (A + B^C + D) and Reaction 2 (C+D—>A-\- B). Reaction i may first be considered by itself. That is, if the solution at the start contains only A and B, it is the only reac¬ tion that can take place at first. The fundamental statement of the Law of Mass Action is that any substance participating in a chemical reaction does so at a rate proportional to its concen¬ tration. In the case of Reaction i, which proceeds with a velocity (zq) proportional to the concentrations of A and B (that is, vx = kx [A] [R]),2 A and B are used up (that is, their concentra¬ tions diminish), and so the velocity of this reaction is greatest at the beginning, and becomes less as time goes on. However, as soon as A and B have begun to react, the prod¬ ucts of their decomposition (C and D) begin to appear, and the concentrations of C and D steadily rise. The velocity (v2) of Reaction 2, which is proportional to the concentrations of C and D (v2 = k2 [C] [R]), was zero at the start (since C and D were absent), but becomes progressively greater as these products accumulate. In view of the fact that the rate of one reaction is constantly decreasing, and the rate of the other reaction constantly increas¬ ing, the two velocities must at some point become equal. When that point has been reached, the two opposing reactions are tak¬ ing place at the same rate, and the process will appear to have stopped. It is then said to have come to equilibrium. 2 See footnote, p. 9.