Particle motion in gases
- The molecules of a gas are in constant random motion.
- The temperature of a gas is related to the average kinetic energy of its molecules: the hotter the gas, the faster they move.
- When the molecules collide with the walls of a container, they exert a force. Pressure is the force per unit area.
Temperature and pressure
- If a gas is heated at constant volume, its molecules move faster.
- They collide with the walls more often and with more force, so the pressure increases.
Pressure and volume (separate sciences)
- A gas exerts a net force at right angles to the walls of its container, or any surface.
- Increasing the volume of a fixed mass of gas at constant temperature decreases its pressure, because the molecules hit the walls less often.
- For a fixed mass of gas at constant temperature: p V = constant, so p₁V₁ = p₂V₂.
Doing work on a gas (Higher, separate sciences)
- Work is done when a gas is compressed, for example in a bicycle pump.
- The work done increases the internal energy of the gas, so its temperature increases. This is why a bicycle pump gets warm.
Key terms
- Pressure
- The force per unit area, caused by gas molecules colliding with surfaces.
- Random motion
- Movement in all directions at different speeds.
- Kinetic energy
- The energy of moving particles; its average is linked to temperature.
- Constant volume
- When a gas is kept in a container that cannot expand.
- Pascal
- The unit of pressure (Pa); 1 Pa = 1 N/m².
- Compression
- Squeezing a gas into a smaller volume.