Assumptions of the Ideal Gas Model and Its Applications
Assumptions of the Ideal Gas Model
- The ideal gas model is based on five key assumptions.
- These assumptions simplify the complex behavior of real gases, allowing us to predict their behavior using mathematical relationships.
1. Gas Particles Are in Constant, Random Motion
- Gas particles are never at rest; they move in straight lines until they collide with another particle or the walls of their container.
- This constant, random motion explains why gases fill any container they occupy, regardless of its shape.
When you spray perfume in a room, the gas molecules disperse evenly, filling the available space.
TipVisualize gas particles as tiny billiard balls moving in random directions and bouncing off walls without losing energy.
2. Collisions Between Gas Particles Are Perfectly Elastic
- When gas particles collide with each other or with the walls of their container, no energy is lost as heat or sound.
- These are perfectly elastic collisions, meaning the total kinetic energy of the system remains constant.
- This explains why the pressure exerted by a gas on its container walls doesn’t decrease over time, as long as temperature and volume remain constant.
Students often assume that gas particles lose energy during collisions, but in the ideal gas model, energy is always conserved.
3. Gas Particles Have Negligible Volume Compared to the Space They Occupy
- Although gas particles have mass and volume, their size is so small compared to the distance between them that we treat their volume as negligible.
- This assumption explains why gases are compressible and why their behavior can be described using simple equations.
- Vaporized water occupies about 1600 times the volume of liquid water at standard temperature and pressure (STP).
- This dramatic expansion illustrates how much empty space exists between gas particles.
4. No Intermolecular Forces Act Between Gas Particles
- In an ideal gas, particles neither attract nor repel each other.
- This assumption allows gas particles to move independently of one another.
- As a result, an ideal gas cannot condense into a liquid, no matter how much the temperature is lowered.
In real gases, intermolecular forces like van der Waals forces become significant at low temperatures or high pressures, causing deviations from ideal behavior.
5. The Kinetic Energy of Gas Particles Is Proportional to Temperature (in Kelvin)
- The average kinetic energy of gas particles is directly proportional to the gas's absolute temperature.
