CORRECTIONS IN ISOPERIBOL CALORIMETRY - A UNIFIED VIEW OF ADIABATIC AND HEAT-FLOW CALORIMETERS

When both temperature change and heat loss, as given by Newton's law of cooling, are inserted into the enthalpy-balance equation of an isoperibol calorimeter, it is possible to transform the observed curve of temperature against time into either of two functions of time. One is directly proportional to the enthalpy change ΔrHm·Δξ due to chemical reaction in the calorimeter, and the other to its time derivative. Algorithms for numerical treatment are given and applied to experiments with the following sources and calculated results: (a) a short electric pulse giving a step-like function; (b) a first-order reaction of several hours' duration where the function was found proportional to the extent of reaction; and (c) constant electric power at several levels which were correctly reproduced by the function. Considerable improvement in precision was obtained. The method clarifies the relation between adiabatic and heat-flow calorimetry, and extends the use of both into the region of finite time. © 1990.