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G. Venkata Ramana ¹, E. Rajagopal ², N. Manohara Murthy ²

Affiliations
1 Sree Lakshmi Sreenivasa Degree College, Pullareddy Peta, Kadapa-516175, IN
2 Department of Physics, Sri Krishnadevaraya University, Anantapur-515003, IN

Abstract

Ultrasonic velocities (u) in dilute solutions of water in diethylamine, triethylamine, dibutylamine and di-sec-butylamine have been determined at 298.15 K using single crystal variable path interferometer working at 3 MHz. Excess ultrasonic velocities (u^E) have been evaluated using thermodynamically valid expression. A distinctive non-linear variations of ultrasonic velocity and excess ultrasonic velocity with concentration (X₂) of water in all the (amine+water) systems have been observed. The linear variation of u and u^E upto certain optimum concentration (X₂)_opt, observed has been explained as due to the existence of water molecules as monomers distributed uniformly throughout the solutions. The non-linear variations of u and u^E versus X₂ beyond (X₂)_opt has been explained in the light of water-water and water-amine interactions leading to the formation of water-amine complexes.

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T. Ramanjappa ¹, E. Rajagopal ², N. Manohara Murthy ²

Affiliations
1 Department of Physics, University of Botswana, Gaborone, BW
2 Department of Physics, Sri Krishnadevaraya University, Anantapur-515003, IN

Abstract

The parameters characterizing thermodynamic fluctuations namely mean square fluctuations of pressure <(ΔP)²>, temperature <(ΔT)²>, number of molecules in a given volume < (ΔN/N)²> and the correlation function of pressure and temperature fluctuations <(ΔP)(ΔT)> in the binary mixtures of CH₃CN + C₆H₆, C₆H₆ + HCON(CH₃)₂ and CH₃CN + HCON(CH₃)₂ at 298.15 K have been evaluated using the data on ultrasonic velocity, density, molar heat capacity at constant pressure and thermal expansion coefficient. The corresponding excess functions have been evaluated considering that the ideal values are additive on mole fraction basis. The variations of <(ΔP)²>^E, <(ΔT)²>^E, < (ΔN/N) >E and <(ΔP)(ΔT)>^E with the mole fraction of the first component are found to exhibit extrema at intermediate concentrations. The residts are explained in the light of modification of the structure of pure liquids as a result of mixing with the other and stability of the structure formed in the mixtures against the various thermodynamic fluctuations present in the liquid state.

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