Summary of "GCSE Physics Revision "Internal Energy""

Summary of "GCSE Physics Revision 'Internal Energy'"

Main Ideas and Concepts:

Internal Energy Definition:
- Internal Energy is the total energy stored within a system by its particles.
- It includes both the Kinetic Energy (due to particle motion) and Potential Energy (due to intermolecular forces and chemical bonds) of all particles (atoms and molecules).
Particle Behavior in States of Matter:
- Solids: Particles vibrate but do not move from place to place.
- Liquids: Particles move around each other.
- Gases: Particles move rapidly and freely.
- All particles possess Kinetic Energy due to their motion.
- Particles also have Potential Energy because of forces between them.
Changes of State and Internal Energy:
- Heating a solid increases its Internal Energy until it melts into a liquid (melting).
- Heating a liquid further increases Internal Energy until it boils into a gas (boiling).
- Cooling a gas reduces Internal Energy until it condenses into a liquid (condensation).
- Cooling a liquid further reduces Internal Energy until it freezes into a solid (freezing).
Additional Points on Changes of State:
- Sublimation: Some solids (e.g., carbon dioxide) can change directly to gas without becoming liquid.
- Mass Conservation: During changes of state, mass remains constant; no particles are lost or gained.
- Physical vs Chemical Changes: Changes of state are physical changes, meaning the material can revert to its original form without altering chemical properties (e.g., melted and refrozen ice remains ice).
Evaporation:
- Evaporation is the process where only the surface particles of a liquid gain enough energy to become gas.
- It differs from boiling because it occurs only at the surface and at temperatures below the boiling point.

Methodology / Key Points to Remember (Bullet Format):

Definition of Internal Energy:
- Sum of kinetic and Potential Energy of all particles in a system.
Particle Movement in States:
- Solid: Vibrate in place.
- Liquid: Move around each other.
- Gas: Move rapidly and freely.
State Changes and Internal Energy:
- Heat solid → increase Internal Energy → melting → solid to liquid.
- Heat liquid → increase Internal Energy → boiling → liquid to gas.
- Cool gas → decrease Internal Energy → condensation → gas to liquid.
- Cool liquid → decrease Internal Energy → freezing → liquid to solid.
Special Cases:
- Sublimation: solid → gas directly.
- Mass is conserved in all state changes.
- State changes are physical, reversible changes.
Evaporation:
- Surface-only liquid to gas transition.
- Occurs at temperatures below boiling point.

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