Model the diffusion of a gas using the particle theory.
The particle theory can also be used to explain diffusion. Diffusion is the spreading out of particles to fill the space they are in.
For example, if somebody spills some perfume in your classroom, your nose will soon pick up the smell. The smell of the perfume quickly spreads through the room. However, you cannot see any perfume in the air.
Perfume is made up of small particles. It has a low boiling point and easily becomes a gas at room temperature.
Diffusion happens by itself. You do not need to mix or stir the substances. Diffusion in gas
1. Spray some perfume at the top of the classroom. a. Predict which students will be the first to smell the perfume.
b. Predict how long it will take for all the students in the room to smell the perfume.
2. Draw a diagram to explain how the smell of the perfume reached your nose (remember to include the air particles that also fill the room).
z Diffusion in liquids
In small groups, set up the investigation shown in Fig. 9.2.2. Your aim is to determine if the temperature of the water has any effect on how the food dye moves in the water.
1. Before you start, predict the results of this investigation and explain your prediction.
2. What will you do to make this investigation a fair test?
3. What did you observe when food colouring was placed in each cup?
4. Explain what happened using the particle model.
z 158 158 Fig. 9.2.2 Hot Medium Cold Food dye Fig. 9.2.1
