Changes of state
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Explainer Video
Summary
Changes of state
In a nutshell
The arrangement of particles in solids, liquids and gases can be changed. This summary will cover how changes between these states can occur and allow you to predict the states of substances.
Particle model
Definition
The arrangement of particles in either solids, liquids or gases due to how much energy they hold.
The particle model explains how particles behave in each of the states.
STATE OF MATTER | PROPERTIES |
 Solid |
|
 |
|
 Gas |
|
However, this model is not perfect. In reality, particles are not perfect spheres - they are ions, atoms, or molecules of different shapes and sizes. In addition, the graphic representation does not show the strength of forces between particles.
State changes
Substances can change states and these changes are also reversible. This is shown below.
State change | Explanation | Example | ||
1. | Deposition | Gas to solid | Particles change from a gas to a solid without passing through the intermediate liquid phase. | Frost formation |
2. | Sublimation | Solid to gas | Particles change from a solid to a gas without passing through the intermediate liquid phase. | Dry ice |
3. | Condensing | Gas to liquid | Particles no longer have enough energy to overcome attractive forces, so bonds form between them. | Water condenses on cold surfaces |
4. | Boiling | Liquid to gas | Particles gain even more energy and vibrate more, breaking the forces holding particles together. This occurs at the boiling point and is known as evaporation. | Water (C) evaporates from a kettle as steam (A) |
5. | Melting | Solid to liquid | Particles gain energy and vibrate more, weakening forces between particles. This occurs at the melting point. | A snowflake (B) melts |
6. | Freezing | Liquid to solid | Particles have even less energy, so more bonds form between them. | Making ice cubes |
Predicting states
You must be able to make predictions on the state of a substance given information such as melting or boiling point.
Rules for state changes:
- If the temperature is below the melting point, the state is solid.
- If the temperature is above the boiling point, the state is gas.
- If the temperature is between melting and boiling point, the state is liquid.
Example
Methanol melts at and boils at . Predict the state of methanol at:
a)
b)
c)
a) Solid; the temperature is below melting point.
b) Liquid; the temperature is between melting and boiling point.
c) Gas; the temperature is above boiling point.
FAQs - Frequently Asked Questions
What does the particle model show?
The particle model explains how particles behave in each of the states.
Is the particle model perfect?
No, the model is not perfect. In reality, particles are not perfect spheres - they are ions, atoms, or molecules of different shapes and sizes.
What is sublimation?
Sublimation is when particles change from a solid to a gas without passing through the intermediate liquid phase.