The isothermal displacement calorimeter: Design modifications for measuring exothermic enthalpies of mixing

Abstract

The isothermal displacement calorimeter described previously has been modified by the inclusion of a thermoelectric cooling module to allow the study of both endothermic and exothermic mixing. Other modifications are also described. Excess enthalpies are reported for 1,4-dioxan+tetrachloro-methane, benzene+dichloromethane, tetrahydrofuran+water, and ethanol+water at 298.15 K and 1,4- dioxan+dichloromethane at 298.15 and 303.15 K. These mixtures have been suggested as possible reference mixtures for either checking the operation of, or calibrating, calorimeters to be used for making measurements on exothermic mixtures. The performances of our calorimeters have been evaluated on the basis of the results presented here and by comparison with previous results. Some advantages and disadvantages of the proposed reference mixtures are discussed. Photochemical effects from the tungsten thermostat lamp affect the results for mixtures of tetra-chloromethane with 1,4-dioxan.