Ethylbenzene, ethylcyclohexane, pentylbenzene, and pentylcyclo-hexane, both pure and binary mixtures, were studied to ascertain the effects ofthe molecular structure and the physical properties of the pure components onresultant properties of the binary mixtures. Density, viscosity, refractive index,isobaric specific heat capacity, and ultrasonic velocity were measured for thepure materials and for the six possible binary mixtures of the four hydrocarbons.Molar volume, isentropic compressibility, isothermal compressibility, and heatcapacity ratio were calculated from the measured quantities. Deviations fromideality were determined as either excess or increment values for each physicalproperty for each mixture. The sign and magnitude of the deviation values varieddepending on the property and the mixture. The isothermal compressibility wassuccessfully calculated from the isentropic compressibility using a well-knownthermodynamic relationship. The isentropic compressibility was found to bealmost a linear function of mixture composition and the difference between theisothermal and isentropic compressibilities was also found to be a smooth function of mixture composition. The difference onlyvaries between 0.15 and 0.22 GPa-1depending on the specific binary mixture. The heat capacity ratio was found to be a smooth, almost linear function of composition
