AIChE Chemical Engineering Jeopardy Practice Exam

Real gases don’t behave like ideal gases because molecules have finite size and attract each other. The van der Waals equation introduces two corrections to capture that: a term that reduces the effective pressure due to attractions, and a term that reduces the available volume due to finite molecular size. The expression P = RT/(V - b) - a/V^2 uses V as molar volume (V_m) and includes these corrections: the denominator (V - b) accounts for the space the molecules cant occupy, while the subtractive a/V^2 term lowers the pressure because intermolecular attractions hold molecules together a bit, especially at higher densities. This form is the standard van der Waals equation of state for a real gas. The other options come from different topics (reaction kinetics and fluid flow) and do not describe a gas’s equation of state.