The Core Principle: Increased Kinetic Energy
Gases expand when heated because increasing the temperature adds kinetic energy to the gas molecules. This causes the individual particles to move faster and with greater force throughout their container or space.
Molecular Collisions and Internal Pressure
As gas molecules move faster, they collide more frequently and more forcefully with each other and with the walls of their container. If the container is flexible or the gas is unconfined, this increased molecular activity naturally pushes the boundaries outward, causing the gas to occupy a larger volume.
Maintaining Equilibrium in an Expanding System
For a gas at constant pressure, a rise in temperature directly leads to an increase in volume. The gas expands until the internal pressure from the more energetic molecular collisions once again equals the external pressure, re-establishing equilibrium at a larger volume.
Real-World Applications of Gas Expansion
This principle is fundamental to many phenomena, from hot air balloons rising as the air inside is heated and expands, to the pressure increase in vehicle tires during warm weather as the air within expands and exerts more force on the tire walls.