1. What Kinetic Theory Tries to Explain
The kinetic theory of gases tries to explain the behaviour of gases by imagining them as made of a huge number of tiny particles moving very fast in all directions. Instead of using large-scale ideas like pressure or temperature, it looks at how individual particles move and collide.
This microscopic viewpoint helps understand why gases expand, why pressure changes, and why temperature is linked to the motion of particles.
2. Gases Are Made of Tiny Moving Particles
According to kinetic theory, a gas consists of extremely small particles (molecules or atoms) that:
- move randomly in all directions
- travel at very high speeds
- collide with each other frequently
- collide with the container walls
2.1. Why This Matters
Many gas properties become easier to understand when we think in terms of particle motion. For example, pressure comes from particles striking the container walls. Temperature is linked to the average kinetic energy of these particles.
3. Macroscopic vs Microscopic View
In thermodynamics, gases are studied using macroscopic quantities like pressure (P), volume (V), and temperature (T). Kinetic theory connects these macroscopic variables to microscopic particle behaviour.
3.1. Connecting the Two Views
- Pressure comes from collisions of particles with the walls.
- Temperature comes from the average kinetic energy of particles.
- Volume is the amount of space available for particle motion.
4. Why Kinetic Theory Is Useful
Kinetic theory helps explain many properties of gases that are difficult to understand using only macroscopic ideas.
4.1. Examples
- Why gases have pressure
- Why pressure increases when temperature increases
- Why gases expand to fill their container
- Why lighter molecules move faster than heavier ones at the same temperature
5. Visualising Particle Motion
Gas particles do not move in straight lines for long. They travel a short distance, collide with another particle, change direction, travel again, and so on. This constant motion and collision behaviour creates the properties we observe at the macroscopic level.
5.1. Simple Example
Imagine releasing perfume in a room. The smell spreads everywhere because the molecules move randomly and collide repeatedly, slowly reaching all corners of the room.