States of Matter
Recap States of Matter for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Use the particle model to explain changes of state, and learn the state symbols (s), (l), (g) and (aq).
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The three states of matter are solid, liquid and gas. The state a substance is in depends on the strength of the forces between its particles.
In a solid the particles are close together in a regular arrangement, vibrating about fixed positions. In a liquid they are close together but arranged randomly and able to move past each other. In a gas they are far apart and move rapidly in all directions.
The amount of energy needed to change state depends on the strength of those forces. Stronger forces mean a higher melting or boiling point. The forces are between the particles, not within the molecules, and confusing the two is the most common error in this topic.
Revision notes
The particle model
Solid: particles close together in a regular arrangement, vibrating about fixed positions.
Liquid: particles close together, randomly arranged, able to move past one another. Gas: particles far apart, moving rapidly in all directions, with negligible forces between them.
Changing state
Melting and boiling occur when the forces between particles are overcome by the energy supplied.
The stronger the forces, the more energy is needed and the higher the melting and boiling points. Freezing and condensing are the reverse processes.
Limitations of the model
The particle model represents particles as solid spheres with no forces between them.
In reality particles are not solid spheres, they are not all the same size, and there are forces between them. Being able to state these limitations is examinable.
Key points
- The three states are solid, liquid and gas.
- Solid particles vibrate about fixed positions.
- Liquid particles move past one another.
- Gas particles move rapidly and are far apart.
- Stronger forces mean higher melting and boiling points.
- The particle model treats particles as solid spheres.
Worked examples
Example 1
Describe the arrangement and movement of particles in a liquid. [2 marks]
Model answer
The particles are close together but arranged randomly (1 mark), and they are able to move past one another (1 mark).
Example 2
Explain why a substance with strong forces between its particles has a high melting point. [2 marks]
Model answer
A large amount of energy is needed to overcome the strong forces between the particles (1 mark), so the substance must be heated to a high temperature before it melts (1 mark).
Example 3
Give two limitations of the simple particle model. [2 marks]
Model answer
It assumes there are no forces between the particles, when in reality there are (1 mark). It represents particles as solid spheres that are all the same size, when in reality they are neither (1 mark).
Common mistakes
Confusing forces between particles with bonds within molecules.
Melting and boiling overcome the forces BETWEEN particles, not the covalent bonds within them.
Saying particles in a solid do not move.
They vibrate about fixed positions.
Saying gas particles have strong forces between them.
The forces between gas particles are negligible.
Not being able to state a limitation of the model.
It is examinable, so learn at least two.
Exam tips
- Describe both arrangement and movement when asked about a state.
- Link melting and boiling points to the strength of forces between particles.
- Learn two limitations of the particle model.
- Keep intermolecular forces and covalent bonds clearly separate.
Key terms
- Particle model
- A model representing matter as small spheres.
- Melting point
- The temperature at which a solid becomes a liquid.
- Intermolecular force
- A force of attraction between particles.
- Change of state
- A physical change between solid, liquid and gas.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.