Explain what happens to the arrangement and movement of particles when a solid is heated until it melts and then heated further until it boils.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The particle model represents the particles in the three states of matter as small solid spheres. Melting and boiling are examples of physical changes.
Model answer (4 marks)
In a solid the particles are in a fixed, regular arrangement and vibrate about fixed positions.
When the solid is heated to its melting point the particles gain kinetic energy, vibrate more vigorously and the forces that hold them in the lattice are overcome. The particles break free from their fixed positions and can move past one another, giving a random arrangement that is still relatively close together.
On further heating to the boiling point the particles gain even more energy, the attractive forces between them are completely overcome and the particles move very rapidly. They are now far apart, spread out and move randomly in all directions, forming a gas.
When the solid is heated to its melting point the particles gain kinetic energy, vibrate more vigorously and the forces that hold them in the lattice are overcome. The particles break free from their fixed positions and can move past one another, giving a random arrangement that is still relatively close together.
On further heating to the boiling point the particles gain even more energy, the attractive forces between them are completely overcome and the particles move very rapidly. They are now far apart, spread out and move randomly in all directions, forming a gas.
Examiner tips
- Use the word "vibrate" for solids, "move past one another" for liquids, and "move rapidly" for gases.
- Mention the increase in kinetic energy and the overcoming of forces.
- Show the change from fixed to random arrangement and from close to far apart.
Mark scheme (4 marks)
- In a solid, particles are held in a regular arrangement / fixed positions
- On melting, particles gain energy and move / break free from their fixed positions so they can move past each other (random arrangement, close together)
- On boiling, particles gain more energy and overcome the forces holding them together / move faster
- In the gas, particles are relatively spread out / far apart and move randomly in all directions
Key terms in this question
Related
- All OCR GCSE Chemistry A: Gateway Science (J248) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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