The Cluster Theory of Imperfect Gases

Abstract

DEVIATIONS from ideality of real gases are generally attributed to the effects of the volume of the molecules and to the attractive forces between them. The volume effect has been described fairly simply and accurately, but explanations put forward as to the way in which the attractive forces act are open to criticism. One of the older common explanations¹ is that the unbalanced attraction inwards on the molecules near the boundary wall results in their being slowed down before they hit the wall, thus giving a lower contribution to the pressure than they would in the absence of attractive forces. As stated, this appears to be a violation of the Principle of Equipartition of Energy. Another way of expressing what is probably the same thing, is often preferred². In this, the deficiency in pressure is attributed to a lower concentration in the boundary layer arising out of a relatively higher potential energy in this layer, due to the attraction inwards. These explanations ignore the fact that adsorption measurements show that all known walls exert a strong attractive force on all gaseous molecules and that the concentration in the boundary layer is invariably higher than that in the body of the gas.