Heat and Thermodynamics

5.5 Comparison of Van der Waals’ Equation with Andrews’ Experimental Curves

The p – v curves for CO₂ obtained from Van der Waals’ equation are similar to the experimental p–v curves of Andrews for CO₂ only at and above the critical temperature. Below the critical temperature, the curves due to Van der Waals’ equations are different from Andrews’ experimental curves. If the isothermals of Andrews’ experimental curves are made to overlap the theoretical curves for the same temperatures, it is found that above the critical temperature the two sets of curves coincide whereas below the critical temperature the two sets of curves are coincident only at the purely gaseous and liquid region, and there is a prominent difference in the central region ( ...