Is the Van der Waals Gas Equation More Accurate Than the Ideal Gas Equation?

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Discussion Overview

The discussion revolves around the comparison between the Van der Waals gas equation and the ideal gas equation, specifically focusing on the accuracy of these models in predicting real gas behavior regarding pressure and volume. Participants explore the implications of molecular volume and interactions at varying pressures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the real pressure is smaller than the ideal pressure and if the real volume is smaller than the ideal volume when using the Van der Waals equation.
  • Another suggests calculating pressure and volume for various cases using both the ideal gas equation and the Van der Waals equation to compare results.
  • A participant reports finding that the real volume is indeed less than the ideal volume but expresses confusion about how the real volume could also be perceived as larger than the ideal volume, particularly at high pressures.
  • Another participant clarifies that the ideal gas law ignores molecular size, which leads to the theoretical prediction of volume compressing to zero at high pressures, while the real volume is significantly larger due to the presence of gas molecules.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are conflicting interpretations regarding the relationship between real and ideal volumes, especially under high-pressure conditions.

Contextual Notes

There are unresolved assumptions regarding the behavior of gases under different conditions, particularly concerning the effects of molecular size and interactions, which may influence the accuracy of the equations being discussed.

requal
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Just wondering, for van der waals equation, the real pressure is smaller than the ideal pressure and the real volume is smaller than the ideal volume?
 
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Check - calculate P&V for several cases using both ideal gas equation and VdV equation.
 
Okay I found out that the real volume is indeed less than the ideal volume, but I don't get how the real volume is bigger than the ideal volume? I thought it would be the other way around because molecular volume becomes significant at high pressures meaning that gases have less free space to move around (because some of the space is taken up by the gas molecules themselves), and hence the real volume would be lower than the ideal volume? No?
 
requal said:
Okay I found out that the real volume is indeed less than the ideal volume, but I don't get how the real volume is bigger than the ideal volume?

This is a little bit convoluted and I have a feeling you are contradicting yourself - volume is less but you don't understand how it is bigger?

Ideal gas ignores molecule size, so at high pressures it theoretically compresses to zero, real volume is much larger than that.
 

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