The isotherms for the VdW fluid (as calculated directly from theVdW equation of state, without performing the Maxwellconstruction)increase monotonically for T > Tc as V isdecreased. For T < Tc , they pass through a maximum and then aminimum before steeply increasing as V is decreased.
What does this tell you about the first and second derivativesof P with respect to V, when the pressure, temperature, and volumeall attain their critical values?
