Journal of Solution Chemistry

, Volume 18, Issue 4, pp 369–377 | Cite as

The effect of pressure on order destruction and order creation in linear or branched alkane mixtures

  • Emilio Aicart
  • Gloria Tardajos
  • Miguel Costas
Article

Abstract

The pressure dependence of the excess enthalpy H E , dH E /dP, has been calculated from experimental excess volumes V E and dV E /dT using dH E /dP=V E −TdV E /dT. dH E /dP at zero pressure are reported at 25°C and equimolar concentration for the mixtures: cyclohexane with the series of normal alkanes (n-C n , where n=6,8,10,12,14 and 16) and with the series of highly branched alkanes (br-C n , where n=6,8,12 and 16), benzene, toluene and p-xylene +n-C n and 1-chloronaphthalene +n-C n and br-C n . Experimental and Flory theory dH E /dP values are in good agreement for the whole cyclohexane +br-C n series. For the n-C n series, dH E /dP becomes increasingly positive deviating from the Flory predictions. This discrepancy is due to the presence of short-range orientational order in the higher n-C n pure liquids which makes dH/dP more negative and which, upon mixing, is destroyed producing a positive contribution to dH E /dP not accounted for by the theory. The discrepancy between theoretical and experimental dH E /dP is large for benzene, but progressively smaller for toluene, p-xylene and 1-chloronaphthalene. These results are consistent with creation of order between the aromatic plate-like molecule and the long n-C n in solution. For 1-chloronaphthalene +n-C n , this order creation process produces a negative contribution to dH E /dP which balances the positive order-destruction contribution originated by the rupture, upon mixing, of short-range orientational order in pure n-C n .

Key words

Short-range orientational order excess enthalpy excess volume excess expansivity pressure normal alkanes branched alkanes, cyclohexane, benzene, toluene,p-xylene, 1-chloronaphthalene 

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Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • Emilio Aicart
    • 1
  • Gloria Tardajos
    • 1
  • Miguel Costas
    • 2
  1. 1.Departamento de Químíca-Física. Facultad de Ciencias QuímicasUniversidad ComplutenseMadridSpain
  2. 2.Departamento de Física y Química Teórica. División de Ciencias BásicasUniversidad Nacional Autónoma de MéxicoMéxicoMéxico

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