In Van der Waals equation, the constants a and b represent what?

• A. Forces and Size
• B. Temperature and Volume
• C. Pressure and Temperature
• D. Moles and Volume

Answer: (A)

The key idea is that real gases don’t behave like ideal gases because there are intermolecular attractions and finite molecular sizes. In the Van der Waals correction, the term a accounts for the attractive forces between molecules—the stronger these attractions, the more they pull gas particles inward, reducing the pressure they exert on the container compared to an ideal gas. The term b accounts for the finite size of molecules—the molecules themselves take up space, so the free volume available for movement is smaller than the container volume, effectively using V minus nb.

So the constants reflect two physical realities: forces pulling molecules together and the actual volume each molecule occupies. This is why the correct description is “forces and size.” The other options mix wrong physical quantities (temperature, pressure, or moles) with the concept, which don’t correspond to what a and b represent.