Simultaneous flow measurement of specific heats and thermal expansion coefficients of liquids: Aqueoust-BuOH mixtures and neat alkanols and alkanediols at 25�C

Abstract

A flow method is described for the simultaneous measurement of volumetric specific heat capacities cpv and thermal expansion coefficients α of liquids, using a Picker heat capacity microcalorimeter. the method involves a simple sequence of operations in which the calorimeter unit is used alternately to measure a difference in volumetric specific heats at constant flow rate and temperature, or a flow rate variation resulting from a temperature scan on a flow cell. The precision of the method in α measurements is close to 1% which is comparable to that of current dilatometric methods; the overall time for the combined cpv-α measurement is less than 30 minutes. Typical uses and reliability of the method are illustrated through results for aqueous NaCl solutions, t-BuOH-water mixtures, and α,ω-diols (C2−C5) at 25°C. The α and cpv values in homologous series of normal alkanes, alcohols and diols appear well represented by equations comprising two contributions, one related to the hydrocarbon chain length, the other dependent on the number density of −OH groups. The general trends in these data and comparison with similar results for H2O2 and H2O illustrate the magnitude of the cpv and α ‘anomalies’ in liquid water.