Blundell Thermal Physics · Problem 9.6

Transport properties in gases

Physics — Statistical Mechanics · eucken-formula-heat-capacity

Problem

In Section 11.3, we will define the ratio of CpC_p to CVC_V as given by the number γ\gamma. We will also show that Cp=CV+RC_p = C_V + R, where the heat capacities here are per mole. Show that these definitions lead to CV=R(γ−1).(9.50)C_V = \frac{R}{(\gamma - 1)}.\tag{9.50} Starting with the formulae CV=CV′+CV′′C_V = C_V' + C_V'' and κ=(52CV′+CV′′)η\kappa = \left(\frac{5}{2}C_V' + C_V''\right)\eta, show that if CV′/R=32C_V'/R = \frac{3}{2}, then κ=14(9γ−5) ηCV,(9.51)\kappa = \frac{1}{4}(9\gamma - 5)\,\eta C_V,\tag{9.51} which is Eucken's formula. Deduce the value of γ\gamma for each of the following monatomic gases measured at room temperatures. [table — see PDF] Deduce what proportion of the heat capacity of the molecules is associated with the translational degrees of freedom for these gases. (Hint: notice the word ``monatomic''.)

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