Diffusion

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Lesson notes

What is Diffusion?

Diffusion is the movement of particles from a **high concentration** to a **low concentration**.
It occurs in **fluids** (liquids and gases).
Diffusion is a **passive** process – no energy input is needed.
Particles move due to their **random motion** (kinetic energy).

Particle Motion in Fluids

In **liquids**, particles are in contact but can flow past each other.
In **gases**, particles are far apart and move quickly in random directions at a range of speeds.
Random motion of particles causes **Brownian motion**.
Particles in a fluid are constantly moving and colliding.

Factors Affecting Diffusion Rate

**Temperature**: higher temperature → particles move faster → diffusion is faster.
**Stirring** (in liquids) speeds up diffusion by distributing particles.
**Concentration gradient**: steeper gradient → faster diffusion.
**Air currents** (e.g., a fan) can speed up diffusion in gases.

Examples of Diffusion

Dye spreading in water: dye particles move from high to low concentration until evenly spread.
Deodorant spreading in a room: gas particles diffuse through the air.
Smell of food cooking travels through the kitchen.

Key Points to Remember

Diffusion is **not** from low to high concentration – that is false.
Diffusion happens in **both** liquids and gases, not just one.
Rate of diffusion increases with temperature.
Stirring or using a fan increases the rate of diffusion.

Particle arrangement in solids, liquids, and gases. Diffusion occurs in liquids and gases where particles can move.

Slides

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Practice questions

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1.Which of the following best describes diffusion?
Easy
- AMovement of particles from a high concentration to a low concentration
- BMovement of particles from a low concentration to a high concentration
- CMovement of particles only in solids
- DMovement of particles only in gases
2.In which states of matter can diffusion occur?
Easy
- ALiquids and gases
- BSolids and liquids
- CSolids and gases
- DSolids, liquids and gases
3.Which of the following statements about diffusion is true?
Easy
- ADiffusion happens at the same rate regardless of temperature
- BDiffusion can be sped up by heating the liquid or gas
- CDiffusion only occurs when a liquid is stirred
- DDiffusion is faster in cold liquids than in hot liquids
4.What type of motion do particles in a liquid or gas exhibit?
Easy
- ARandom motion
- BVibrational motion only
- CCircular motion
- DStraight-line motion only
5.Two beakers contain water at different temperatures. Beaker A is at 20 °C, Beaker B is at 50 °C. Red dye is added to both. In which beaker will the dye spread faster?
Medium
- ABeaker A, because cold water has more space between particles
- BBeaker B, because the particles have more kinetic energy and move faster
- CBeaker A, because diffusion is slower at higher temperatures
- DBeaker B, because hot water has fewer particles
6.A student sprays deodorant in a room. How does the deodorant spread throughout the room?
Medium
- ABy convection currents only
- BBy diffusion of deodorant particles from high to low concentration
- CBy evaporation of the liquid into the air
- DBy the force of gravity pulling the particles
7.A fan is turned on in a room where deodorant has been sprayed. What effect does this have on the rate of diffusion?
Medium
- AIt decreases the rate because the fan blows particles away
- BIt increases the rate because the fan mixes the air, moving particles faster
- CIt has no effect on the rate of diffusion
- DIt stops diffusion completely
8.Which of the following is an example of Brownian motion?
Hard
- AThe movement of pollen grains suspended in water as seen under a microscope
- BThe spreading of a smell across a room
- CThe flow of water through a pipe
- DThe movement of a gas from a high-pressure to a low-pressure region

Revision notes

## Diffusion - **Definition**: Diffusion is the movement of particles from a **high concentration** to a **low concentration**. - **Occurs in**: Fluids (liquids and gases) only. - **Cause**: Random motion of particles. - In **liquids**: particles are in contact, free to flow past each other. - In **gases**: particles are separate, move quickly in random directions at a range of speeds (causes Brownian motion). - **Example**: Dye dropped in water spreads from high to low concentration until evenly distributed. - **Speeding up diffusion**: - **Increase temperature**: particles move faster → diffusion faster. - **Stirring** (liquids) or using a **fan** (gases) also speeds up diffusion. - **Key point**: Diffusion is faster at higher temperatures because particles have more kinetic energy and move faster.

Diffusion: The movement of particles from a high concentration to a low concentration.
Fluid: A substance that can flow; includes liquids and gases.
Random motion: Movement of particles in unpredictable directions, caused by collisions.
Brownian motion: The random movement of particles suspended in a fluid, caused by collisions with fast-moving molecules.
Concentration: The amount of a substance in a given volume; high concentration means many particles per unit volume.

Flashcards

What is diffusion?

Diffusion is the movement of particles from a high concentration to a lower concentration.

In which states of matter does diffusion occur?

Diffusion occurs in fluids: liquids and gases.

How do particles move in a liquid?

Particles in a liquid are in contact with each other and free to flow past each other, moving with random motion.

How do particles move in a gas?

Particles in a gas are separate from one another and move quickly in random directions at a range of speeds.

What is Brownian motion?

Brownian motion is the random movement of particles in a fluid caused by collisions with other particles.

What happens to dye dropped into water?

The dye particles diffuse from a high concentration where they are dropped to areas of lower concentration, eventually spreading evenly throughout the water.

How can diffusion in a liquid be sped up?

Diffusion can be sped up by heating the liquid (particles move faster) or by stirring the liquid.

True or false: In diffusion, particles move from a low concentration to a high concentration.

False. In diffusion, particles move from a high concentration to a lower concentration.

True or false: Diffusion happens at the same rate regardless of temperature.

False. Diffusion is faster at higher temperatures because particles move faster.

True or false: Diffusion happens only in liquids.

False. Diffusion happens in both liquids and gases (fluids).

True or false: Diffusion in a liquid can be sped up by stirring.

True. Stirring speeds up diffusion.

What happens to the average speed of particles in a liquid when temperature increases?

The average speed of particles increases as temperature increases.

Two beakers of water at 20°C and 50°C have dye added. Which diffuses faster?

Beaker B at 50°C diffuses faster because the particles have more kinetic energy and move faster.

How does deodorant spread throughout a room?

Deodorant particles diffuse from a high concentration near the spray to lower concentration areas, spreading throughout the room.

What effect does a fan have on the rate of diffusion?

A fan speeds up diffusion by moving air and increasing particle movement.

What is a fluid?

A fluid is a substance that can flow, such as a liquid or a gas.

Describe the random motion of particles in a gas.

Gas particles move quickly in random directions at a range of speeds, and they are separate from one another.

Describe the random motion of particles in a liquid.

Liquid particles are in contact but free to flow past each other, moving randomly.

What is the final result of diffusion over time?

Particles become evenly distributed throughout the space, reaching equilibrium.

Why does heating a liquid speed up diffusion?

Heating increases particle kinetic energy, making them move faster and spread more quickly.

Why does stirring a liquid speed up diffusion?

Stirring moves particles around, increasing the rate of mixing and spreading.

What is the concentration gradient?

The difference in concentration between two areas; diffusion occurs down the concentration gradient (high to low).

Does diffusion occur in solids?

No, diffusion occurs only in fluids (liquids and gases), not in solids.

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