What do the van der Waals constants a and b represent?

What do the van der Waals constants a and b represent?

• A. a represents molecular size; b represents intermolecular attractions.
• B. a represents the rate constant; b represents volume.
• C. a accounts for intermolecular attractions; b accounts for finite molecular size.
• D. a and b have no physical meaning.

Answer: (C)

The van der Waals equation introduces corrections to account for real-gas behavior. The constant a captures the strength of intermolecular attractions; these attractions pull molecules toward each other, lowering the pressure the gas would exert at a given volume and temperature. The constant b represents the finite size of molecules; because molecules take up space, the actual free volume available for movement is reduced by nb, so you replace V with V minus nb in the equation. That’s why the correct interpretation is that a accounts for intermolecular attractions and b accounts for finite molecular size. The other options either swap these ideas, misidentify them as rate or volume without physical meaning, or claim there’s no physical meaning, which isn’t accurate for the van der Waals model.

The van der Waals equation introduces corrections to account for real-gas behavior. The constant a captures the strength of intermolecular attractions; these attractions pull molecules toward each other, lowering the pressure the gas would exert at a given volume and temperature. The constant b represents the finite size of molecules; because molecules take up space, the actual free volume available for movement is reduced by nb, so you replace V with V minus nb in the equation.

That’s why the correct interpretation is that a accounts for intermolecular attractions and b accounts for finite molecular size. The other options either swap these ideas, misidentify them as rate or volume without physical meaning, or claim there’s no physical meaning, which isn’t accurate for the van der Waals model.