1.5.2 real gases

chem modelsofparticulatenatureofmatter

Structure 1.5.2 - real gases deviate from the ideal gas model, particularly at low temperature and high pressure

there is no such thing as an ideal gas. real gases deviate to some extent from ideal behaviour as the assumptions that:

• gas particles occupy a negligible volume compared to the volume the gas occupies
• there are no intermolecular forces between gas particles
  do not apply under all conditions

1. the volume of gas particles is not negligible
   if the volume isn’t negligible, then they would travel less distance between collisions with the wall, so collisions would be more frequent than predicted by the ideal gas model and the pressure is greater.

this is most noticeable at high pressures and low temperatures when the particles are confined in a small volume and the distance between the particles are significantly reduced.

2. there are attractive forces between the particles

when a particle approaches the wall of a container, attractive forces will pull it in the opposite direction, reducing the speed of the colliding particle, leading to a less energetic collision with the wall, leading to a lower pressure than predicted by the ideal gas.

this reduction in speed is most significant when the average speed is relatively low

read more in 1.5.3 and 1.5.4 the ideal gas laws