Describe the pressure and the changes in pressure of a gas in terms of the motion of its particles and their collisions with a surface

What is Pressure?

Pressure is the force that a gas exerts on the walls of its container, divided by the area of those walls.

Mathematically: \$P = \dfrac{F}{A}\$

Think of a crowded classroom: the more students (particles) push against the walls, the higher the pressure.

How Particles Create Pressure

Particles move randomly and collide with the walls. Each collision transfers a tiny bit of momentum.

• More collisions per second → higher pressure.
• Faster particles → each collision delivers more force.
• Heavier particles → more momentum per collision.

Imagine a room full of ping‑pong balls (particles) bouncing around. The more balls and the faster they bounce, the harder they hit the walls.

Changing Pressure: Temperature, Volume, and Number of Particles

Pressure depends on three key factors:

1. Temperature (T) – hotter particles move faster.
2. Volume (V) – a smaller space means more collisions per unit area.
3. Number of Particles (N) – more particles = more collisions.

In equations:

\$P \propto \dfrac{N m \bar{v^2}}{V}\$

Where \$m\$ is particle mass and \$\bar{v^2}\$ is the average of the square of particle speed.

⚡ Quick rule of thumb: Increase temperature → ↑ pressure; decrease volume → ↑ pressure; increase number of particles → ↑ pressure.

Exam Tips

• Show the relationship between pressure and temperature using the ideal gas law: \$PV = nRT\$.
• Explain that pressure changes when \$T\$, \$V\$, or \$n\$ change.
• Use the particle picture: “When the particles move faster (higher T), they hit the walls more forcefully, so pressure rises.”
• Remember to include units: pressure in pascals (Pa) = N/m².
• Practice sketching a simple diagram of particles colliding with a wall and label the force and area.