Deviations from Ideal Gas Law

[FatherTime-PhD]

Hi,
Thanks in advance for answer this

I'm having a lot of trouble understanding the reasoning behind deviations from the idea gas law.
I understand that Ideal Gases occur under Low Pressure and High temperature but I'm having trouble understanding, on a molecular level, why high pressure and low temperature cause deviation.

According to Kaplan: As pressure of gas increases, particles pushed closer together (makes sense). At moderately high pressure, a gas' volume is LESSS than would be predicted by ideal gas law due to intermoleculer attraction (DOES NOT MAKE SENSE).

I thought ideal gases assumed negligible volume ... so if if volume is less than would be be predicted (which predicted = negligible) ... how does that make sense ... what am I missing?

And the temperature explanation confuses me to.

Thanks!!!

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[FatherTime-PhD]

Also, I'm having trouble reconciling all of this with something like kinetics or Keq ... where increasing temperature increases these values because of more interaction ... but for whatever reason here, gasses have more interactions at low temperature?

 

[sunshine859]

The ideal gas law does NOT assume negligible volume. It states that PV=nRT, or V=(nRT)/P. In regard to your question, think of the ideal gas law as a way to predict the volume of a gas at "normal" conditions. Say, for example, at normal conditions, you calculate the volume of a gas to be 5 L. Now, let's say the gas is at a high pressure. Like you mentioned, there is more intermolecular interaction at high pressure. This causes the molecules of the gas to essentially stick closer to one another. If they're stuck closer to one another, they take up less space, hence, at high pressure, let's say the true volume is 4.5 L, lower than what would be predicted by the ideal gas law.

 

[ManhattanEliteMCAT]

Hello,

At low temperatures, attractions between gas particles cause the particles to collide less often with the container walls, resulting in a pressure lower than the ideal gas value. The behavior of real gases usually agrees with the predictions of the ideal gas equation to within 5% at normal temperatures and pressures. At low temperatures or high pressures, real gases deviate significantly from ideal gas behavior.

Ideal gas according to the kinetic model theory states that the conditions that apply are high temperatures where kinetic energy and pressure is too high and the interactions between the containers are negligible. Hence, the deviations of ideal gas falls when there is low temperature and high pressure.