by the gas molecules themselves in the case of high density (real) gases. On noting that the critical isotherm on the P-v diagram has a horizontal inflection point at the that the Van derWaals constant a and b are given as: \mathbf{a}=\frac{27 \mathbf{R}^{2} \mathrm{~T}_{\mathbf{C r}}^{2}}{\mathbf{6 4 P}_{\mathbf{\alpha}}} ; \quad \mathbf{b}=\frac{\mathbf{R T}_{\mathbf{\alpha}}}{\mathbf{8 P}_{\mathbf{C}}} where Pa and Tr are the critical pressure and critical temperature of the gas respectively.
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