When do gases behave ideally?

An ideal gas has no interactions between constituent molecules and all the collisions taking place between those molecules are perfectly elastic. These conditions are necessary for an ideal gas to exist.

No gas can be perfectly ideal but real gases can behave like ideal ones. Gases need high temperatures and low pressures to behave ideally. This is because the molecules of gases are faster at high temperatures and molecules have a large free volume around them at low pressures.

  • High temperature increases the kinetic energy of the gas molecules. This makes them able to overcome intermolecular interactions that exist between all real particles.
  • Low pressure increases free volume around molecules. This increases the elasticity of collisions among particles.

The real gases having properties near to perfect gases should have molecules far away from each other so that they may not interfere with the properties and functions of one another. Similarly, to decrease the energy wastage due to intermolecular collisions, molecules must have a maximum distance among particles.

Conditions for an ideal gas Behavior

An ideal gas must have the following properties:

  1. A constant motion of molecules.
  2. Negligible actual volume.
  3. No intermolecular forces among particles.
  4. Perfectly elastic collisions among particles.
  5. Kinetic energy equal to the absolute temperature.

Ideal gases obey all gas laws under all conditions of pressure and temperature. Whereas real gases obey gas laws under high temperature and low pressure only.