Excess Heat Capacities of Binary Mixtures at 298 K

Abstract

We constructed a differential flow microcalorimeter designed by Picker et al. in order to measure excess heat capacities of binary mixtures and checked the reproducibility of the calorimeter by using aqueous NaC1 solutions, because Desnoyers suggested it as a standard chemical solution. We obtained the following equation for the apparent molar heat capacity, c_{p, φ}: C_{p, φ} =-82.46+20.59 m^1/2+35.86 m-11.37 m^3/2 This result is a little smaller than that of Picker et al. but the error is believed to be about 1% of 50JK^-1⋅ mol^-1.
Using this calorimeter, we measured excess heat capacities, C_p^E of following binary mixtures:
1) Heptane cyclohexane and + benzene
2) Carbon tetrachloride + benzene and -I toluene In the heptane system, C_p^E is negative but in the carbon tetrachloride system, C_p^E is positive. The experimental results are at variance with the Prigogine-Flory corresponding state theory which predicts C_p^e= 0. It may be explained in terms of the difference in the molecular orientation in pure components and the mixture, which is suggested by Patterson et al.