A SIMPLE DIFFERENTIAL THERMOMETRIC TECHNIQUE FOR MEASURING RATES OF CHEMICAL REACTIONS IN SOLUTIONS

This paper describes the construction and operation of a constant-temperature-environment differential twin microcalorimetric apparatus for following the rate of a chemical reaction by monitoring the difference between the temperature of a reaction mixture, contained in one of two identical vessels, with that of a reference solution contained in the other. The temperatures are sensed by thermistors, whose resistances are compared in a simple Wheatstone bridge. Data on the reaction between ethyl acetate and sodium hydroxide indicate that second-order rate constants can be evaluated with accuracies and precisions of a few per cent or better even if the overall change of temperature during a reaction is as small as 0.015°. Various tests for internal consistency indicate that the measured differential temperatures are reliable to ± 20 μdeg or better.