Why Does the Van der Waals Equation Adjust Pressure Up and Volume Down?

In summary, the Van der Waals equation adjusts pressure up and volume down in order to account for the fact that gas molecules are not point masses and actually occupy some volume, as well as to take into consideration the effects of intermolecular attractions and inelastic collisions on the pressure of a gas. This allows for a more accurate calculation of the pressure of a gas, as the ideal gas law equation (PV = nRT) does not account for these factors.
  • #1
Qube
Gold Member
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Homework Statement



Why does the Van der Waals equation adjust pressure up and volume down?

Homework Equations



(P + a)(V-b) = nRT (overly simplified, but it gets the point across).

The Attempt at a Solution



Okay. Volume refers to total free volume in a container in the context of the gas law. I can understand why volume is adjusted down relative to the ideal gas law equation (PV = nRT). Gases aren't point masses and actually occupy some volume.

However, why is pressure adjusted up? Gas molecules may attract and participate in inelastic collisions. This would seem to decrease the actual pressure. Why then would pressure need to be adjusted up?
 
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  • #2
Qube said:
Gas molecules may attract and participate in inelastic collisions. This would seem to decrease the actual pressure.
If you were to measure the pressure of a gas with ##a = 0##, and then, with everything else the same, with ##a > 0##, how would the measurements differ?
 

FAQ: Why Does the Van der Waals Equation Adjust Pressure Up and Volume Down?

1. What is the Conceptual Van der Waals Question?

The Conceptual Van der Waals Question is a theoretical problem in the field of thermodynamics and statistical mechanics. It is used to understand the limitations of the van der Waals equation of state, which is used to describe the behavior of real gases.

2. Who proposed the Conceptual Van der Waals Question?

The question was first proposed by Dutch physicist Johannes Diderik van der Waals in 1873. He used it to challenge the assumptions of the ideal gas law and to develop a more accurate equation of state for real gases.

3. What are the key components of the Conceptual Van der Waals Question?

The key components of the question are the concepts of volume exclusion and intermolecular interactions. These factors were not considered in the ideal gas law, but are essential for understanding the behavior of real gases.

4. How is the Conceptual Van der Waals Question answered?

The question is typically answered by using the van der Waals equation of state, which takes into account volume exclusion and intermolecular interactions. This equation allows for more accurate predictions of gas behavior, especially at high pressures and low temperatures.

5. What are the practical applications of the Conceptual Van der Waals Question?

The Conceptual Van der Waals Question has important applications in many fields, including chemistry, physics, and engineering. It is used to understand and predict the behavior of real gases in various systems, such as industrial processes, atmospheric conditions, and biological systems.

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