Excess molar enthalpies of (toluene + n-heptane) and (toluene + methylcyclohexane) using a new variable-volume dilution calorimeter

Abstract

A new variable-volume isothermal dilution calorimeter has been designed and constructed, with the variability in volume provided by use of flexible metal bellows. A computerized control and data-acquisition system has been developed using a digital PID control algorithm to control the calorimeter heater, with temperature variations during injections held to within a few mK. This new calorimeter concept is believed to be capable of rapid and precise measurements of excess molar enthalpies H m E for both endothermic and exothermic (liquid + liquid) and (gas + liquid) mixtures over wide ranges of temperature. The performance of this calorimeter has been evaluated by employing (cyclohexane + n-hexane) as a standard test mixture at 298.15 K. Experimental H m E results agree within 0.5 J · mol −1 (0.2 per cent of H m, max E) with the best previous results for this test mixture. New H m Es were produced for (toluene + n-heptane) and (toluene + methylcyclohexane) at the same temperature.