STUDENT SPACE · TOPIC 4

Gas pressure and Brownian motion

Explain gas pressure under controlled conditions and distinguish Brownian motion from molecular motion.

The essentials

Gas pressure results from particles colliding with container walls.
At constant volume, heating a fixed amount of gas increases pressure: particles move faster and collisions are more frequent and forceful.
At constant temperature, reducing the volume of a fixed amount of gas increases the frequency of collisions with the walls.
Brownian motion is the irregular movement of visible particles caused by uneven collisions with much smaller, moving particles.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

A sealed, rigid container of gas is warmed. Predict the pressure change and explain it using particles.

Need a hint for Question 1?

The amount of gas and container volume stay constant. What changes about collisions?

Check Question 1

Pressure increases. Particles move faster, so they collide with the walls more often and with greater force.

A fixed amount of gas is compressed at constant temperature. Predict its pressure change and explain.

Need a hint for Question 2?

Average particle speed stays the same. Think about wall collisions.

Check Question 2

Pressure increases because particles collide with the walls more frequently in the smaller volume.

Smoke particles move irregularly under a microscope. What causes this motion?

Need a hint for Question 3?

The visible particles are much larger than air molecules.

Check Question 3

Uneven collisions with rapidly moving air molecules cause the smoke particles to move irregularly. This is Brownian motion.

For more written practice, use Lesson 4 in your worksheet. Your teacher will discuss those answers in class.

Use the Phase Changes tab. Add heat and observe the particles and pressure reading while keeping the amount of gas and container volume fixed.