Real Gas At Very High Pressure

[rowjimmy]

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I know that at very high pressure a real gas will have a greater volume than what would be predicted by the ideal gas law equation, but would the pressure of the gas be greater, equal, or less than what would be predicted by the ideal gas law equation. What about at moderate pressure?

From looking at the van der Waals equation I would predict that under very high pressures, as volume increases, the pressure deviation from ideality is lessened but pressure would still be less (because volume is in the denominator of the portion that corrects its deviation from ideality). At lower pressures where volume is lower, real pressure will be even less than what was predicted by the ideal gas equation under extremely high pressure conditions because the pressure deviation from ideality under moderate pressure conditions is greater because the correction factor is greater (volume in the denominator decreases, thereby increasing the amount that needs to be added to the real pressure to make it near ideal).

Let me know if this sounds right. Thanks!!

 

[dmf2682]

I know that at very high pressure a real gas will have a greater volume than what would be predicted by the ideal gas law equation, but would the pressure of the gas be greater, equal, or less than what would be predicted by the ideal gas law equation. What about at moderate pressure?

From looking at the van der Waals equation I would predict that under very high pressures, as volume increases, the pressure deviation from ideality is lessened but pressure would still be less (because volume is in the denominator of the portion that corrects its deviation from ideality). At lower pressures where volume is lower, real pressure will be even less than what was predicted by the ideal gas equation under extremely high pressure conditions because the pressure deviation from ideality under moderate pressure conditions is greater because the correction factor is greater (volume in the denominator decreases, thereby increasing the amount that needs to be added to the real pressure to make it near ideal).

Let me know if this sounds right. Thanks!!

This is probably out of scope for the mcat.

 

[chiddler]

I don't understand your reasoning, but the way I understand it is that real pressure is less than ideal pressure because the gases exert intermolecular attractions. Therefore, the force of banging on the walls of a container are reduced and pressure is reduced.

Does increasing the volume reduce this? Yes, because pressure is lower not because the volume is smaller. Smaller pressure means fewer gas particles interacting and therefore less deviation from ideal behavior. At high pressure, gas particles are swamped together in a shorter average distance and therefore can exhibit more forces on each other.