Some features of heat capacity changes in aqueous solutions of low molecular weight alkanols at T = 298.15 K and ambient pressure

Abstract

The specific (cp) and molar (Cp) heat capacities of dilute aqueous solutions of methanol (MeOH), ethanol (EtOH), 1-propanol (n-PrOH) and 2-propanol (i-PrOH) were measured using an adiabatic calorimetry at T = 298.15 K and ambient pressure. Based on the obtained results, the excess molar heat capacities, CpE, as well as the apparent molar heat capacities of each of components, Cp,∅,12, of the system {water (1) + alkanol (2)} were calculated. The standard (at infinite dilution) Cp,2o values were also estimated. All the CpE values are positive and pass through maxima, which shift to the range of a lower mole fraction of alcohol, x2, when the molecular weight of the latter increases. The same goes for the Cp,∅,1max values, too. In turn, the order of changing Cp,∅,2max within the narrow high-diluted range of (∼0.01 <x2 < 0.035) m.f. is oppositely directed. It is established that the x2 value at dCpE/dx2 = 0 is approximately half of the sum of the x2 values at Cp,∅,1max and Cp,∅,2max, a fact indicating the parity contribution of both interacting components of the solution to the structure-energy transformations occurring in it.