Pressure and Temperature in Gases

Gas particles are far apart and move randomly. When they hit the walls of a container, they push on it. This push per unit area is called pressure.

How pressure changes

• At fixed temperature, squeezing a gas into a smaller volume makes more frequent wall collisions, so pressure rises. Boyle’s law: $p \propto 1/V$.
• At fixed volume, heating makes faster collisions, so pressure rises. Pressure law: $p \propto T$ (T in kelvin).

How temperature changes volume

Heating increases particles’ average kinetic energy. If pressure is kept constant (for example, a loose balloon), the gas expands. Charles’ law: $V \propto T$ (T in kelvin; $T(\mathrm{K}) = \, ^\circ\!\mathrm{C} + 273$).

Everyday links

• Balloons shrink in a freezer and grow in warm air.
• Aerosol cans become dangerous if heated: pressure increases in the fixed can volume.
• Pushing a syringe plunger halves the volume, roughly doubling pressure (if temperature stays the same).

Common misconceptions

• Heating does not make particles bigger; it makes them move faster.
• Use kelvin for gas laws, not °C.