Abstract |
A thermodynamic relationship among excess ultrasound speed, excess molar volume and excess molar isentropic compression of liquid mixtures is revisited. The consequences of this relationship, which stems from the Newton-Laplace equation, are discussed. The constraints for possible values taken by Balankina s relative excess properties, that is, ratios between excess and ideal quantities, are further developed. It is demonstrated that, besides the requirement for, if two of these properties attain extreme values at a common exact composition, then the remaining one also takes an extreme value at that composition, further constraints apply to the signs of their rate of change with composition. Using accurate literature data for a binary liquid mixture possessing small positive relative excess molar volumes over the entire composition range, coupled with large positive relative excess ultrasound speeds and large negative relative excess molar isentropic compressions, it is shown that the thermodynamic equations under scrutiny are numerically verified. It is concluded that present theoretical developments can confidently be used for testing the thermodynamic consistency of experimentally determined excess properties of liquid mixtures. (C) 2012 Elsevier B.V. All rights reserved. |