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  • Viscosity Of Hard Sphere Gases – Chemistry Notes – For W.B.C.S. Examination.
    Posted on November 25th, 2019 in Chemistry
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    Viscosity Of Hard Sphere Gases – Chemistry Notes – For W.B.C.S. Examination.

    হার্ড স্ফিয়ার গ্যাসের সান্দ্রতা – রসায়ন নোট – WBCS পরীক্ষা।

    The pressure in a dilute hard sphere gas is calculated, starting from the virial theorem and making use of the ergodic hypothesis. The time development of the system is described within the ’’sucessive uncorrelated binary collision approximation.’’Continue Reading Viscosity Of Hard Sphere Gases – Chemistry Notes – For W.B.C.S. Examination.

    The results obtained are applied to calculate the time correlation function for the bulk viscosity. As is well known, only the potential part of the time correlation function gives a nonvanishing contribution to the bulk viscosity. It is shown that for hard spheres the time correlation function is just a δ function without an exponentially decaying contribution.

    The well-known formula for calculating the viscosity of hard sphere gases, ηo = 2(mkT)1/2/3π3/2σ2, where σ2 is molecular cross section, is altered to ηo = K(MT)1/2/Vt2/3, where Vt is the molal volume of a liquid that has expanded sufficiently to permit mean free paths long enough to have significant fractions of the random thermal momenta of molecules in free flight and M is molal mass.

    This formulation places upon a single straight line points for all nonpolar molecules, mono- and polyatomic molecules alike, over long ranges of temperature.The ratios D/DE (where D is diffusion coefficient and DE is the Enskog dense fluid diffusion coefficient) for smooth hard spheres, and η/ηE (η being shear viscosity and ηE the Enskog dense fluid viscosity) for methane, are used in conjunction with equivalent hard spheres diameters (σϱ) derived from liquid densities on solid-liquid coexistenxe curves to examine (a) application of the smooth hard spheres (SHS) model to self-diffusion in the liquefied rare gases; (b) application of the Chandler rough hard spheres (RHS) model to diffusion and viscosity of the complex molecular liquids carbon tetrachloride, benzene, acetonitrile, carbon disulphide, 1,2-dichloroethane, mesitylene, octamethylcyclotetrasiloxane and deuteromethanol. Predictions of the SHS model are satisfactory for the liquefied rare gases provided that σϱ values are corrected to allow for less dense liquid packing, at temperatures approaching the triple points, than for hard spheres.

    Translational- rotational coupling factors for diffusion (AD) and in some cases viscosity (Aη) for the complex molecular liquids show all four kinds of temperature (T) and density (ϱ) dependence: (i) independent of T and ϱ (CS2); (ii) temperature-dependent, density-independent (CH3CN, CH2OD); (iii) density-dependent, temperature-independent (CCl4); (iv) density and temperature- dependent (benzene).

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