States and properties of matter

Characteristics of gases

Diffusion

Atomic structure

Electronic configuration and valency

MYP Chemistry Diffusion Notes

What Is Diffusion?

Have you ever noticed how the scent of perfume spreads across a room, or how a drop of ink slowly spreads out in water?

This process is called diffusion.

This happens naturally because all particles are in constant random motion.

Definition

Diffusion

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

Analogy

Consider a crowded room where people are standing very close together.
If the doors open to an empty hallway, people will naturally walk out and spread into the free space.
Over time, the people become more evenly spread out.
This spreading out is similar to diffusion.

The Particle Model and Diffusion

The particle model helps us understand why diffusion occurs in different states of matter.

Note

Diffusion can be described using the particle model: particles are always moving, and over time their random motion causes them to spread out and mix.

These properties of gases, liquids, and solids perfectly describe diffusion:

Gases:

Particles are far apart, move very quickly and collide frequently.
This allows gases to diffuse rapidly.

Liquids:

Particles are closer together than in gases, but they still have enough energy to move around each other.
Diffusion still happens, but usually more slowly than in gases.

Solids:

Particles are packed very closely and can only vibrate around fixed positions.
Diffusion in solids is therefore extremely slow and often negligible at everyday temperatures.

Common Mistake

Note

Try not to confuse diffusion with sedimentation.
- Diffusion: Particles move in all directions due to random motion, spreading out from high to low concentration.
- Sedimentation: Particles settle to the bottom of a container because of gravity, usually when they are large or dense.
Both processes can happen at the same time, but they are not the same.
Particles that are diffusing are still moving randomly through the fluid, while sedimented particles have mostly collected at the bottom and are no longer spreading through the fluid.

Example

Ammonium Chloride Ring

A classic experiment demonstrates diffusion in gases using ammonia gas (NH₃) and hydrogen chloride gas (HCl).

The two gases are released at opposite ends of a long glass tube.
As they diffuse along the tube, they meet and react to form a white solid, ammonium chloride (NH₄Cl).
The white ring forms closer to the HCl end because NH₃ molecules have a lower relative mass and diffuse faster than HCl molecules.

Potassium Permanganate in Water

Diffusion in liquids can be seen using potassium permanganate (KMnO₄):

A small crystal of KMnO₄ is placed gently in a beaker of water.
At first, the purple colour is concentrated near the crystal.
Over time, the colour spreads throughout the water as KMnO₄ particles diffuse between the water particles.

Why Diffusion Is Slower in Liquids than in Gases

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MYP Chemistry Diffusion Notes

What Is Diffusion?

The Particle Model and Diffusion

Ammonium Chloride Ring

Potassium Permanganate in Water

Why Diffusion Is Slower in Liquids than in Gases

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What Is Diffusion?

The Particle Model and Diffusion

Ammonium Chloride Ring

Potassium Permanganate in Water

Why Diffusion Is Slower in Liquids than in Gases

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Periodic table5 subtopics

Matter5 subtopics

Types of chemical reaction18 subtopics

International Union of Pure and Applied Chemistry (IUPAC)4 subtopics

Pure and impure substances2 subtopics

The atmosphere2 subtopics

Bonding4 subtopics

MYP Chemistry Diffusion Notes

Periodic table5 subtopics

Matter5 subtopics

Types of chemical reaction18 subtopics

International Union of Pure and Applied Chemistry (IUPAC)4 subtopics

Pure and impure substances2 subtopics

The atmosphere2 subtopics

Bonding4 subtopics

What Is Diffusion?

The Particle Model and Diffusion

Ammonium Chloride Ring

Potassium Permanganate in Water

Why Diffusion Is Slower in Liquids than in Gases

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

What Is Diffusion?

The Particle Model and Diffusion

Ammonium Chloride Ring

Potassium Permanganate in Water

Why Diffusion Is Slower in Liquids than in Gases

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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