Gases exhibit remarkable uniformity in physical behaviour regardless of their chemical identity. The ideal gas is a theoretical model that allows generalised mathematical treatment.
Assumptions of the Ideal Gas Model
You must be able to state these clearly in exam responses:
Continuous Random Motion
Gas particles are in constant, rapid, random straight-line motion in all directions.
Negligible Particle Volume
The particles possess negligible volume compared to container space (the gas is mostly empty space).
Zero Intermolecular Forces
There are no attractive or repulsive intermolecular forces between the gas particles.
Perfect Elastic Collisions
All particle collisions are perfectly elastic with zero net dissipation of kinetic energy.
Avogadro's Law and Molar Volume
Avogadro's Law (V ∝ n)
Equal volumes of any gases, measured under identical conditions of temperature and pressure, contain the same number of particles (moles): \(V \propto n\).
Molar Volume at STP (22.7 dm³ mol⁻¹)
IUPAC defines Standard Temperature and Pressure (STP) as 273.15 K (0 °C) and 100 kPa (10⁵ Pa). Under STP conditions, one mole of any ideal gas occupies exactly 22.7 dm³ (0.0227 m³).
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