Calculate the molar volume of oxygen gas at 298. K and 136. bar (2000 lb/in², the pressure in a filled laboratory gas cylinder), using the van der waals equation. How does this value compare with the ideal gas law value?

This problem requires solving the van der Waals equation for . The equation is:. It is cubic in the volume and its solution is not straight-forward. A single equation can be solved in Mathcad using a solve block. The solve block consists of the word Given, the equation to be solved, and the Find function. The solve block is preceded by a guess value for the unknown variable

Since the equation is cubic there are three roots. The function Find returns the root which is the closest to the initial guess value. A reasonable guess value for in this case, is the ideal gas law value:

Guess value

Use control = for the = sign

Percent deviation from ideality=