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2.7Unit 3: Forces, motion and pressure

Particles on the move — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 7 of 7 1 quiz

📚 Cambridge Checkpoint Physics 0893 Hub / Topical Revision
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Lesson summary

2.7 Particles on the move — CHECKPOINT PHYSICS 0893 notes: Explain diffusion in gases and liquids and the factors that change its speed.In a gas — both the speed and the direction of the particles are randomMixed gases — each gas spreads to fill the whole containerDiffusion = the…

  • Concentration
  • Stops when
  • After diffusion stops
  • Random movement
  • Ink in water
  • Tea in water

Part 1 of 7Random movement of particles

Random movement of particles
In a gas
  • In a gas both the speed and the direction of the particles are random
Mixed gases
  • Mixed gases each gas spreads to fill the whole container

Part 2 of 7Diffusion

Diffusion
Diffusion the overall random movement of particles from an area of higher concentration to an area of lower concentration
Concentration
Concentration the number of particles in a particular volume
Stops when
  • Stops when the concentrations are equal everywhere
After diffusion stops
  • After diffusion stops the particles carry on moving randomly

Part 3 of 7Diffusion of two gases

1
At the start a tap is closed, with one gas on the left and another on the right.
2
The tap is opened and particles of each gas pass through at random.
3
Each gas spreads to the other side, so the concentrations become more equal.
4
After some time both gases are at equal concentration on both sides.
5
Diffusion stops, but individual particles still move.

Part 4 of 7Smell of cooking food

Source
  • Source heated food releases particles that change state to gas
Spreading
  • Spreading these particles move randomly and spread through the air by diffusion
Strength
  • Strength the smell is stronger closer to the food because the concentration is higher
Animals
  • Animals many animals use the change in strength of smell to find food

Part 5 of 7Diffusion in liquids

Random movement
  • Random movement particles in a liquid also move at random
Ink in water
  • Ink in water blue ink moves from a high concentration to low concentration until it is spread evenly
Tea in water
  • Tea in water tea diffuses through the water of a cup

Part 6 of 7Speed of diffusion

FactorEffect on speed of diffusion
Bigger difference in concentrationFaster diffusion
Higher temperatureFaster diffusion because particles move faster
Lower temperatureSlower diffusion

Part 7 of 7Temperature and diffusion investigation

1
Add equal volumes of water at different temperatures to beakers and record each temperature.
2
Add a small volume of ink carefully to the bottom of each beaker with a dropper pipette.
3
Time how long the ink takes to spread through the water in each beaker.
4
Record the results in a table.
5
Describe the trend: the higher the temperature, the shorter the time.
6
Keep the volume of water the same to make it a fair test.

Key terms

TermMeaning
DiffusionSpreading of particles from high to low concentration.
ConcentrationNumber of particles in a given volume.
RandomWithout a pattern in speed or direction.
GasState with particles moving freely and randomly.
Equal concentrationSame number of particles per volume everywhere.

Avoid these mistakes

1
Thinking diffusion stops all particle movement — particles keep moving at random.
2
Thinking diffusion only happens in gases — it also happens in liquids.
3
Thinking particles move in one direction in diffusion — movement is random, but overall they spread from high to low concentration.
4
Thinking diffusion is faster in cold water — it is faster in hot water.

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