Skip to main content
Chemistry LibreTexts

Real Gases - Joule-Thomson Expansion

  • Page ID
  • The Joule-Thomson effect is also known as the Joule-Kelvin effect. This effect is present in non ideal gasses, where a change in temperature occurs upon expansion.


    The Joule-Thomson coefficient is given by

    \[\mu_{\mathrm JT} = \left. \dfrac{\partial T}{\partial p} \right\vert_H\]


    • T is the temperature,
    • p is the pressure and
    • H is the enthalpy.

    In terms of heat capacities one has

    \[\mu_{\mathrm JT} C_V = -\left. \dfrac{\partial E}{\partial V} \right \vert_T \]


    \[\mu_{\mathrm JT} C_p = -\left. \dfrac{\partial H}{\partial p} \right \vert_T \]

    In terms of the second virial coefficient at zero pressure one has

    \[\mu_{\mathrm JT}\vert_{p=0} = ^0\!\!\phi = B_2(T) -T \dfrac{dB_2(T)}{dT}\]


    1. Jacques-Olivier Goussard and Bernard Roulet "Free expansion for real gases", American Journal of Physics 61 pp. 845-848 (1993)
    2. E. Albarran-Zavala, B. A. Espinoza-Elizarraraz, F. Angulo-Brown "Joule Inversion Temperatures for Some Simple Real Gases", The Open Thermodynamics Journal 3 pp. 17-22 (2009)
    3. Thomas R. Rybolt "A virial treatment of the Joule and Joule-Thomson coefficients", Journal of Chemical Education 58 pp. 620-624 (1981)


    • Was this article helpful?