Edexcel iGCSE Physics -5.9P Changes of State- Study Notes- New Syllabus
Edexcel iGCSE Physics -5.9P Changes of State- Study Notes- New syllabus
Edexcel iGCSE Physics -5.9P Changes of State- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.
Key Concepts:
5.9P describe the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas
Changes of State: Melting, Evaporation and Boiling
When a substance changes state, energy is transferred to or from its internal energy store. During a change of state, the temperature remains constant even though energy is still being transferred.
Melting: Solid → Liquid
What happens during melting
- The solid is heated until it reaches its melting point.
- Energy continues to be transferred to the substance.
- The temperature stays constant at the melting point.
Particle explanation
- Particles in a solid vibrate about fixed positions.
- Heating increases the particles’ energy.
- Energy is used to overcome the forces holding particles together.
- Particles can move past each other and form a liquid.
Energy changes
- Kinetic energy stays constant.
- Potential energy increases.
- Internal energy increases.
Evaporation: Liquid → Gas (Below Boiling Point)
What happens during evaporation
- Evaporation can occur at any temperature.
- Only the fastest-moving particles escape from the liquid surface.
- The remaining liquid cools down.
Particle explanation
- High-energy particles escape from the surface.
- Average kinetic energy of remaining particles decreases.
- Temperature of the liquid falls.
Energy changes
- Energy is taken from the liquid.
- Internal energy of the liquid decreases.
Boiling: Liquid → Gas (At Boiling Point)
What happens during boiling
- Boiling occurs at a fixed temperature called the boiling point.
- Bubbles of gas form throughout the liquid.
- The temperature remains constant while boiling.
Particle explanation
- All particles gain enough energy to escape.
- Forces between particles are overcome.
- Particles move freely as a gas.
Energy changes
- Kinetic energy stays constant.
- Potential energy increases.
- Internal energy increases.
Evaporation vs Boiling
| Evaporation | Boiling |
|---|---|
| Occurs at any temperature | Occurs at fixed temperature |
| Occurs at surface only | Occurs throughout liquid |
| Causes cooling | No temperature change |
Key Idea
- Changes of state require energy.
- Temperature remains constant during a change of state.
- Energy is used to change particle arrangement, not speed.
Important Points to Remember
- Melting and boiling increase internal energy.
- Evaporation removes energy from a liquid.
- Particle model explains all changes of state.
Example
Ice at 0°C is heated until it becomes water at 0°C.
Explain what happens to the particles during this process.
▶️ Answer / Explanation
Energy is transferred to the ice.
The energy is used to overcome forces between particles.
Particles leave their fixed positions and can move past each other.
The temperature remains constant.
Example
Wet clothes dry on a cool day.
Explain how evaporation causes this.
▶️ Answer / Explanation
Some high-energy water particles escape from the surface.
This happens even below the boiling point.
The remaining liquid loses energy and dries.