Kinetic particle model of matter
States of matter, the particle model, temperature, internal energy and changes of state.
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Before you begin
Everything is made of tiny particles that are always moving, and how they are arranged and how fast they move explains why solids keep their shape, liquids flow and gases fill their container. The lessons start by comparing the three states of matter and explaining their properties with the particle model. They then link temperature to the kinetic energy of the particles, describe internal energy and explain why melting and boiling happen without a change in temperature.
Be comfortable with: physical quantities and units, because temperature is measured in °C or K.
Learning goals
- Compare physical properties of solids, liquids and gases
- Explain state properties using particle arrangement, motion, forces and separation
- Relate temperature rise to increased average kinetic energy of particles
- Describe internal energy as the total kinetic energy of the particles' random motion plus the total potential energy between them
- Describe melting, solidification, boiling and condensation as energy transfers without a change in temperature
Syllabus statements covered
- compare the physical properties of solids, liquids and gases
- use the kinetic particle model to describe the different states of matter (solids, liquids and gases), relating their physical properties to the arrangement and motion of the particles (e.g. molecules, atoms) and the forces and distances between particles
- relate the rise in temperature of a body to the increase in average kinetic energy of all the particles in the body
- describe internal energy as an energy store that is made up of the total kinetic energy associated with the random motion of the particles and the total potential energy between the particles in the system
- describe melting/solidification and boiling/condensation as processes of energy transfer without a change in temperature
Lessons
Work through them in order.
- States of matter and the particle modelCompare solids, liquids and gases, and explain each of their properties with the arrangement, motion, separation and forces of their particles.
- Temperature and internal energyRelate temperature to average particle kinetic energy and compare the internal energy of samples with different masses, temperatures and states.
- Heating and cooling curvesIdentify states on heating and cooling curves and explain how energy is transferred during slopes and plateaux.
Practise and check
Topic reference
Quick reference
| State | Arrangement of particles | Motion of particles | Forces between particles |
|---|---|---|---|
| solid | close together, in a fixed pattern | vibrate about fixed positions | strong |
| liquid | close together, no fixed pattern | move around each other | weaker |
| gas | far apart, random | move quickly in all directions | very weak |
| Idea | Meaning |
|---|---|
| temperature | rises when the average kinetic energy of the particles increases |
| internal energy | total kinetic energy of the particles’ random motion + total potential energy between them |
| change of state | energy is transferred but the temperature stays the same |
Core knowledge to remember
- The kinetic particle model describes solids, liquids and gases in terms of the arrangement and motion of their particles and the forces and distances between them.
- A rise in the temperature of a body is linked to an increase in the average kinetic energy of all its particles.
- Internal energy is made up of the total kinetic energy of the random motion of the particles and the total potential energy between them.
- Melting, solidification, boiling and condensation are processes of energy transfer without a change in temperature.
Common mistakes
- Saying the particles themselves expand or melt. The particles stay the same; their arrangement and motion change.
- Saying temperature is the total energy of a sample. It depends on the average kinetic energy of the particles.
- Saying the temperature rises while a substance melts or boils. The energy changes the potential energy of the particles instead.
- Saying the particles in a solid do not move. They vibrate about fixed positions.