STUDENT SPACE · TOPIC 5

Diffusion and chapter review

Explain diffusion-rate differences and apply the particle model across the chapter.

The essentials

Diffusion happens because particles move randomly; the net movement is down a concentration gradient.
Higher temperature increases particle speed and usually increases the rate of diffusion.
At the same temperature, lighter gas molecules diffuse faster than heavier gas molecules.

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

Two gases at the same temperature have relative molecular masses of 17 and 36.5. Which is expected to diffuse faster?

Need a hint for Question 1?

Compare molecular mass while keeping temperature the same.

Check Question 1

The gas with relative molecular mass 17 diffuses faster because its molecules have a higher average speed at the same temperature.

Why does the same gas usually diffuse faster at a higher temperature?

Need a hint for Question 2?

Link temperature to average kinetic energy and particle speed.

Check Question 2

Higher temperature increases average kinetic energy and speed, so particles spread more quickly.

Two gases are compared at different temperatures. Is this a fair test of how molecular mass affects diffusion? Explain.

Need a hint for Question 3?

Identify a second factor that changes diffusion rate.

Check Question 3

No. Temperature also affects particle speed. Keep temperature and other conditions the same when comparing the effect of molecular mass.

For more written practice, use Lesson 5 in your worksheet. Your teacher will discuss those answers in class.

Compare particle motion before and after heating the same substance. The simulation illustrates motion; it does not directly measure diffusion rates.