# A small amount of perfume is sprayed at one end of a long room. After a few minutes, the scent can be detected at the other end of the room. Explain why the scent spreads through the room and why it would spread more slowly on a cold day than on a warm day.

> Cambridge International IGCSE Chemistry (0620) — 1.2 Diffusion · Explain · 4 marks

## Mark scheme (4 marks)

1. Perfume molecules move/spread from an area of high concentration to an area of low concentration
2. Perfume molecules are in constant/random motion
3. On a cold day, perfume molecules have less (kinetic) energy / move more slowly
4. Slower-moving molecules take longer to spread/diffuse across the room, so diffusion is slower

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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