5.1 The Gaseous State
Kinetic theory of gases
- Assumptions made in the kinetic theory of gases as applied to ideal gases:
- The gas particles have zero intermolecular forces between them
- The gas particles behave as point particles which have negligible volume.
- The gas particles are in constant random motion, colliding with each other and the wall of the container frequently
- All collisions between the gas particles are perfectly elastic
- Pressure is due to the collision of gas particles with the wall of container
- In the gaseous state, the particles can move freely and are far apart.
- A gas has no ftxed shape and volume, it takes the shape of container and always fills The volume of a gas depends on its pressure, temperature and number of moles.
Ideal gas and real gas
- A real gas is most like an ideal gas at:
i. low pressures
- At low pressures, the distance between gas particles is large and the volume of the gas particles is negligible(very small compared to the volume of the container).
- Intermolecular forces are also negligible at low pressures.
ii. high temperatures(well above its boiling point)
– At high temperatures, the gas particles have negligible intermolecular forces between them because they have sufficient energy to overcome it.
- However, an ideal gas does not exist, because:
- there are intermolecular forces between the gas particles
- the volume occupied by the gas particles is not zero
- A real gas shows biggest deviation from an ideal gas at:
i. high pressures
- At high pressures, the gas particles are packed close together, thus the volume occupied by the gas particles is not negligible
- The intermolecular forces between them is also not negligible
ii. low temperature
- At low temperatures, the gas particles are packed close together, thus the volume occupied by the gas particles is not negligible
- The intermolecular forces between them is also not negligible because they do not have sufficient energy to overcome it
The general gas equation
