Conditions when real gases behave as ideal gases

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Discussion Overview

The discussion revolves around the conditions under which real gases approximate ideal gas behavior, focusing on the effects of pressure and temperature. Participants explore the implications of intermolecular forces and distances in relation to the kinetic theory of gases.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that real gases behave like ideal gases at low pressure and high temperature, proposing that the fast movement of gas molecules at high temperatures compensates for attractive forces at low pressures.
  • Another participant questions the reasoning behind why high pressure and low temperature do not lead to ideal gas behavior, indicating that repulsive forces dominate at high pressures due to close molecular proximity.
  • A participant recalls the assumptions of the kinetic theory, noting that molecules are considered to have negligible size and that there are no intermolecular forces apart from collisions.
  • Further discussion highlights that at low pressure and high temperature, intermolecular distances are large, leading to negligible intermolecular forces, which aligns with the ideal gas postulates.
  • A participant raises a question about the real gas equation, specifically the correction term for pressure, asking whether it accounts for attractive forces, repulsive forces, or both, and whether the value of "a" changes under different conditions.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding regarding the behavior of real gases under different conditions, with some agreement on the effects of pressure and temperature, but no consensus on the specifics of the correction term in the real gas equation.

Contextual Notes

The discussion does not resolve the complexities surrounding the correction term in the real gas equation, nor does it clarify the conditions under which the value of "a" may change.

jd12345
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Well i know real gases behave as ideal gas (almost) when pressure is low and temperature is high. I want to understand this - When pressure is low attractive forces in the gas moelcules will be stronger(as compared to high pressure) but the fast movement due to high temperature compensates it? Am i right?

Why can't it be high pressure and low temperature? Because of high pressure repulsive forces dominate ( because molecules will be very close) but then you lower the temperature and moelcules don't move very fast and that compensates for the repulsive forces

Anything wrong in my reasoning. Please help!
 
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Do you remember assumptions used in the kinetic theory?
 
Yes - molecules have negligible size
no intermolecular forces
elastic collisions
 
No intermolecular forces or negligible intermolecular forces (apart from collisions).

Start from there. What can you say about intermolecular distances in the gas that has a low pressure and a high temp?
 
well in case of low pressure and high temperature - there will be large intermolecular distances so negligible intermolecular forces. So it well behave as an ideal gas. I understand now - thank youAnd if there is high pressure there will be repulsive forces and small distances which does not match with the postulates. Thank you again

But one more question - not closely related to my previous question
In the real gas equation pressure is P + an2/V2. Is the correction term only for attractive forces , only for repulsive forces or both? If its for both does that mean value of "a" changes according to conditions
 

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