Study on Isochoric Specific Heat Capacities for Liquid Methanol-Water Mixtures

Published

November 1, 2002

Author(s)

Hiroshi Kitajima, Hiroyuki Miyamoto, Noboru Kagawa, Joe W. Magee, Harumi Endo, Seizo Tsuruno, Koichi Watanabe

Abstract

Hydrogen bonding of water (H₂O) is certain to introduce an effect of the molecular energy to the heat capacity. Due to the presence of the strong hydrogen bonding, interactions between water and methanol (CH₃OH) molecules show anomalous thermodynamic properties. Measurements of the thermodynamic properties are essential to characterize such interactions and to model this behavior with an equation of state. Specific heat capacity at constant volume (c_v) is one of the most important thermodynamic properties to develop and evaluate equations of state. With this point of view, c_v values of water, methanol and their mixtures were measured with an adiabatic calorimeter developed at the National Defense Academy. The calorimeter (fig. 1) is a twin-cell type whose sample and reference cells (33cm³) and their shields were heated by electric power. The cells were surrounded by high vacuum. During the experiment, the heating power was carefully controlled so that the cell temperature increased uniformly. The reference cell was always evacuated and was heated with a constant current. Absolute temperatures were measured with a platinum resistance thermometer (PRT) on the bottom of each cell and were reported on the ITS-90. The experimental uncertainty of temperature measurements is plus or minus} 13 mK, and that of pressure measurements is plus or minus} 8 kPa. The expanded relative uncertainty for c_v is estimated to be 2 % for liquid phase measurements, and for density it is about 0.16 %. Figure 2 shows measured c_v of CH3OH + H20} with x = (0.059, 0.354, 0.503, 0.708) that were measured by our laboratory. Also excess molar isochoric heat capacities c_v^E_m were calculated with an aid of reliable equation of state for both components (Fig. 3). Measured densities with x = (0.503, 0.708) were compared with published data and the result showed good agreement between them.

Proceedings Title

Proc. Japan Symp. on Thermophysical Properties

Conference Location

Tokyo, 1, JA

Conference Title

Japan Symp. on Thermophysical Properties

Pub Type

Conferences

Citation

Kitajima, H. , Miyamoto, H. , Kagawa, N. , Magee, J. , Endo, H. , Tsuruno, S. and Watanabe, K. (2002), Study on Isochoric Specific Heat Capacities for Liquid Methanol-Water Mixtures, Proc. Japan Symp. on Thermophysical Properties, Tokyo, 1, JA (Accessed June 2, 2024)