The thermodynamic method of Eyring and Hirschfelder has been employed to evaluate intermolecular free lengthLfwhereas free length theory FLT of Jacobson was used to compute the theoretical data of ultrasonic sound velocityCFLT. A maximum variation of 0.06% is observed between experimental velocity and the velocity deduced from free length theory (Cexp>CFLT), while uncertainty forCexpdata is as high as ±0.02%. The ultrasonic velocity dataCFLTand densitypof pentanol in water have been used to compute coefficient of thermal expansion α, isothermal compressibility βT, ratio of heat capacity γ, internal pressurepiand pseudo-Gruneisen parameter Γ for the system. The results confirm that, upon increasing the temperature of the system, the solutions become easier to compress.