A method of measuring the velocity of very rapid chemical reactions

Abstract

In devising methods for determining the velocity of any chemical reaction there are two experimental problems which invariably arise : (1) To arrange that the chemical system under investigation be made initially unstable in a period of time that is negligibly short in comparison with that taken by the chemical reaction. (2) To record from time to time the stages reached by the system (during its passage from the initial unstable state to the final stable condition wherein the several reacting substances are in chemical equilibrium) by means of methods which take a negligibly short time in comparison with that taken by the chemical reaction. A perusal of the literature shows that previous investigators have, in the main, restricted themselves to the study of slow reactions, such as may require many minutes or even hours to reach completion. In such cases, both requirements which we have mentioned can be easily met. For the production of the initially unstable condition can be achieved without difficulty by merely mixing the several reacting substances together in proportions far removed from those which prevail when equilibrium has been attained. The time required by the mixing operation can be reduced to a few seconds, and can therefore be neglected when dealing with a process which may last many minutes or even hours. The slow reactions possess a further attraction, in that the procedure for estimating the concentrations of the several reactants at different stages during the progress of the reaction need not be a hurried one. This permits the use of a wide variety of methods, e. g ., polarimetry as in the study of the inversion of sucrose, ordinary titration as in the saponification of esters, and separation of one of the constituents as a gas phase as in the decomposition of diazo-acetic ester by water, i. e ., N 2 . CHCOOC 2 H 5 +H 2 O→OHCH 2 . COOC 2 H 5 +N 2 (gas phase).