Real Gases (DP IB Chemistry): Revision Note

Real gases

• The ideal gas equation (PV = nRT) assumes:

  • Gas particles have negligible volume

  • There are no intermolecular forces

• Real gases deviate from this behaviour, especially at:

  • Low temperatures (stronger attractions between particles)

  • High pressures (particle volume becomes significant)

Graph to show deviation from ideal gas behaviour

Assumptions about volume

• Ideal gases assume gas particles take up no space

• At high pressure, particles are close together, so their volume becomes significant

• This reduces the available space for movement, causing deviation from the ideal gas law

Diagram to show gas volumes at low and high pressure

Assumptions about attractive forces

• Ideal gases assume there are no intermolecular attractions

• At low temperatures, attractions between molecules become significant

• This reduces the frequency and force of collisions with the container walls, leading to a lower pressure than predicted