Diffusion

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课程笔记

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.

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练习题

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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?
Easy
- 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?
Easy
- 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?
Medium
- 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

更多题目

9.What happens to the average speed of particles in a liquid when the temperature is increased?
Easy
- AIt decreases
- BIt stays the same
- CIt increases
- DIt becomes zero
10.A drop of blue dye is placed in a beaker of water. After some time, the water becomes uniformly blue. This is due to:
Easy
- AConvection currents in the water
- BDiffusion of dye particles from high to low concentration
- CEvaporation of the water
- DChemical reaction between dye and water
11.Which of the following statements is false?
Easy
- ADiffusion can occur in gases
- BDiffusion can occur in liquids
- CDiffusion can occur in solids
- DDiffusion is faster at higher temperatures
12.The diagram shows two gas jars, one containing bromine gas (brown) and the other containing air. When the divider is removed, the brown gas spreads into the air jar. This is an example of:
Medium
- ADiffusion because bromine particles move from high to low concentration
- BDiffusion because air particles move into the bromine jar
- COsmosis because the gases mix
- DBrownian motion because the particles are visible
13.A student places a crystal of potassium permanganate at the bottom of a beaker of water. After one hour, the water is uniformly purple. Which process explains this?
Easy
- ADiffusion
- BOsmosis
- CActive transport
- DBrownian motion
14.A beaker of water at 30°C has a drop of blue dye added. After 5 minutes, the dye has spread 2 cm. In a second beaker at 60°C, how far would the dye spread in the same time?
Medium
- AMore than 2 cm
- BLess than 2 cm
- CExactly 2 cm
- DCannot be determined
15.Two gas jars are connected by a narrow tube. Jar A contains nitrogen gas at 1 atm, jar B contains oxygen gas at 1 atm. The tube is opened. After some time, the gases are uniformly mixed. What is the ratio of nitrogen to oxygen molecules in jar A after mixing?
Hard
- A1:1
- B2:1
- C1:2
- DDepends on molecular masses
16.A student observes smoke particles under a microscope. The particles appear to jitter and move randomly. This phenomenon is called:
Easy
- ABrownian motion
- BDiffusion
- COsmosis
- DEvaporation
17.Which of the following will increase the rate of diffusion of a gas into air?
Medium
- AIncreasing the temperature
- BDecreasing the temperature
- CDecreasing the concentration of the gas
- DIncreasing the volume of the container
18.The diagram shows a container divided by a permeable membrane. Left side has 10% sugar solution, right side has 20% sugar solution. Which direction will water move by diffusion?
Medium
- AFrom left to right
- BFrom right to left
- CNo net movement
- DSugar moves instead
19.A student places a drop of food colouring in a beaker of cold water and another in a beaker of hot water. Which beaker will become uniformly coloured first?
Easy
- AHot water
- BCold water
- CBoth at the same time
- DNeither will become uniform
20.Diffusion occurs in which states of matter?
Easy
- ALiquids and gases
- BSolids and liquids
- CSolids and gases
- DSolids, liquids, and gases
21.A gas diffuses through a porous barrier. The time taken for diffusion is inversely proportional to the square root of the molar mass. Which gas diffuses fastest?
Hard
- AHydrogen (H₂)
- BOxygen (O₂)
- CCarbon dioxide (CO₂)
- DChlorine (Cl₂)
22.A student measures the time for a smell to travel across a room. She repeats the experiment with a fan on. What happens to the time?
Easy
- ADecreases
- BIncreases
- CStays the same
- DCannot predict
23.Which of the following best describes the movement of particles in a gas?
Easy
- ARandom and fast
- BRandom and slow
- COrdered and fast
- DOrdered and slow
24.A drop of ink is placed in a beaker of water. After one hour, the ink has spread evenly. Which statement is true?
Medium
- AThe ink particles moved from high to low concentration
- BThe water particles moved from high to low concentration
- CBoth ink and water particles moved equally
- DNo net movement occurred
25.A student sets up an experiment to investigate the effect of temperature on diffusion. Two beakers of water are placed on a bench. Beaker X is at 20°C, beaker Y is at 50°C. A drop of red dye is added to each at the same time. Which beaker will become uniformly coloured first, and why?
Medium
- ABeaker Y, because the particles have more kinetic energy and move faster.
- BBeaker X, because cooler water has less movement so the dye spreads more evenly.
- CBeaker Y, because the dye dissolves faster in hot water.
- DBeaker X, because diffusion is slower at higher temperatures.
26.A student places a crystal of potassium permanganate at the bottom of a beaker of water. After one hour, the water is uniformly purple. Which process explains this observation?
Easy
- ADiffusion
- BConvection
- COsmosis
- DEvaporation
27.A beaker of water at 30°C has a drop of blue dye added. After 5 minutes, the dye has spread 2 cm from the drop. In a second beaker at 60°C, how far would the dye spread in the same time, assuming the rate of diffusion doubles for every 10°C rise?
Hard
- A4 cm
- B8 cm
- C16 cm
- D6 cm
28.A student sets up an experiment to compare diffusion rates of two gases, ammonia (NH₃, M = 17 g/mol) and hydrogen chloride (HCl, M = 36.5 g/mol). Cotton wool soaked in each solution is placed at opposite ends of a glass tube. A white ring of ammonium chloride forms where the gases meet. Which statement is correct?
Hard
- AThe white ring forms closer to the ammonia end because ammonia diffuses faster.
- BThe white ring forms closer to the hydrogen chloride end because ammonia diffuses faster.
- CThe white ring forms exactly in the middle because both gases diffuse at the same rate.
- DThe white ring forms closer to the ammonia end because hydrogen chloride diffuses faster.
29.A student investigates diffusion using a Petri dish of agar gel containing a pH indicator. Wells are cut and filled with acid or alkali. After 30 minutes, a coloured zone appears around each well. Which factor would NOT affect the distance the colour spreads?
Medium
- AThe size of the well
- BThe temperature of the agar
- CThe concentration of the acid or alkali
- DThe colour of the pH indicator
30.Which of the following best describes particle motion in a liquid?
Easy
- AParticles vibrate about fixed positions.
- BParticles move with random motion and can flow past each other.
- CParticles move rapidly in random directions and are far apart.
- DParticles are stationary.
31.Diffusion occurs in which of the following?
Easy
- ASolids only
- BLiquids only
- CGases only
- DLiquids and gases
32.What is Brownian motion?
Easy
- AThe movement of particles from high to low concentration
- BThe random movement of particles in a fluid
- CThe movement of particles due to gravity
- DThe movement of particles in a straight line
33.Which statement about diffusion is correct?
Easy
- AParticles move from a low concentration to a high concentration.
- BParticles move from a high concentration to a low concentration.
- CParticles move only in gases.
- DParticles move only when stirred.
34.What happens to the rate of diffusion when the temperature of a liquid is increased?
Easy
- AIt decreases.
- BIt stays the same.
- CIt increases.
- DIt stops.
35.A drop of red dye is placed in a beaker of water at 20°C. A second drop is placed in water at 50°C. In which beaker will the dye spread fastest?
Easy
- AThe 20°C beaker
- BThe 50°C beaker
- CThey spread at the same rate
- DNeither spreads
36.How does stirring affect the rate of diffusion in a liquid?
Easy
- AIt decreases the rate.
- BIt has no effect.
- CIt increases the rate.
- DIt reverses the direction of diffusion.
37.A student sprays deodorant in a room. Which process explains how the smell spreads?
Easy
- AConvection
- BDiffusion
- CBrownian motion
- DOsmosis
38.Which of the following is a correct description of particle motion in a gas?
Easy
- AParticles vibrate about fixed positions.
- BParticles move slowly and are closely packed.
- CParticles move quickly in random directions at a range of speeds.
- DParticles move in straight lines at constant speed.
39.What is the definition of diffusion?
Easy
- AThe movement of particles from a low concentration to a high concentration
- BThe movement of particles from a high concentration to a low concentration
- CThe random motion of particles in a fluid
- DThe movement of particles due to gravity
40.A fan is turned on in a room where deodorant has been sprayed. What happens to the rate of diffusion?
Medium
- AIt decreases because the fan blows particles away.
- BIt increases because the fan mixes the air.
- CIt remains the same.
- DIt stops completely.
41.Diffusion is the movement of particles from a high concentration to a low concentration.
Easy
True or false?
42.Diffusion occurs only in gases.
Easy
True or false?
43.Increasing the temperature of a liquid decreases the rate of diffusion.
Easy
True or false?
44.Stirring a liquid can speed up diffusion.
Easy
True or false?
45.Which of the following best describes the movement of particles in a liquid?
Easy
- AParticles vibrate about fixed positions.
- BParticles move with a random motion and are free to flow past each other.
- CParticles are stationary.
- DParticles move in straight lines at constant speeds.
46.What is the term for the random movement of particles in a fluid?
Easy
- ADiffusion
- BBrownian motion
- COsmosis
- DEvaporation
47.In which of the following can diffusion occur? (Select all that apply.)
Medium
- ASolids
- BLiquids
- CGases
- DVacuum
48.Match each description to the correct state of matter.
Medium
- Particles are in contact but free to flow past each other
- Particles are separate and move quickly in random directions
- Particles only vibrate about fixed positions
- Liquid
- Gas
- Solid
49.Arrange the following steps in the correct order to describe how a drop of dye diffuses in water.
Medium
- Dye particles are at high concentration at the drop
- Dye particles move from high to low concentration
- Dye particles spread randomly due to water particle collisions
- Dye becomes evenly distributed throughout the water
50.Which of the following factors will increase the rate of diffusion in a liquid? (Select all that apply.)
Medium
- AIncreasing the temperature
- BStirring the liquid
- CUsing a larger container
- DUsing a smaller concentration difference
51.Complete the sentence using the correct word.
Easy
Diffusion is the movement of particles from a ____ concentration to a ____ concentration.
52.Describe how particles move in gases.
Easy
53.A beaker of water at 30°C has a drop of blue dye added. After 5 minutes, the dye has spread 2 cm from the drop. In a second beaker at 60°C, how far would the dye spread in the same time? (Assume the rate of diffusion doubles for every 10°C increase.)
Hard
54.Describe how particles move in a liquid.
Easy
55.A student observes that a smell spreads across a room in 10 seconds at 20°C. If the temperature is increased to 40°C, the average speed of the particles doubles. Assuming diffusion rate is proportional to particle speed, how many seconds will the smell take to spread across the same room at 40°C?
Medium
56.Explain why a drop of ink spreads out when placed in a beaker of water.
Medium
57.A beaker of water at 30°C has a drop of blue dye added. After 5 minutes, the dye has spread 2 cm from the drop. In a second beaker at 60°C, how far would the dye spread in the same time? (Assume the rate of diffusion doubles for every 10°C increase.)
Hard
- A7 cm
- B9 cm
- C10 cm
- D8 cm
58.A student observes that a smell spreads across a room in 10 seconds at 20°C. If the temperature is increased to 40°C, the average speed of the particles doubles. Assuming diffusion rate is proportional to particle speed, how many seconds will the smell take to spread across the same room at 40°C?
Medium
- A7 s
- B4 s
- C5 s
- D6 s

复习笔记

## 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.

闪卡

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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