Heat capacity of solutions by flow microcalorimetry

Abstract

A differential flow microcalorimeter has been designed for the measurement of heat capacities of solutions. Under steady-state condition, it is possible to obtain directly the ratio of the heat capacity of a solution to that of its solvent without any knowledge of the heat capacity of the instrument, the flow rate, or the induced change in temperature. The steady state is reached within 1 min. The overall precision on heat capacity changes is 0.5 per cent and the limit of detectability is 7 × 10 −5 JK −1 g −1 . As a check for reproducibility, the apparent molar heat capacities of aqueous solutions of NaCl in the range 0.01 to 2 mol kg −1 and of urea in the range 0.1 to 10 mol kg −1 were measured at 297.3 K.