P3 - Internal Energy

What is internal energy?

The total kinetic energy and potential energy of all the particles (atoms and molecules) in a system

What two types of energy make up internal energy?

Kinetic energy and potential energy

What gives particles kinetic energy?

Their movement - particles move and vibrate

What gives particles potential energy?

Intermolecular forces and chemical bonds between them

What is meant by a "system" in physics/chemistry?

The material or group of particles being studied

Why do solids have low kinetic energy?

Because particles only vibrate in fixed positions

Why do gases have high kinetic energy?

Because particles move rapidly and freely

What happens to internal energy when you heat a substance?

Internal energy increases

What happens to internal energy when you cool a substance?

Internal energy decreases

What happens to a solid when it is heated?

It melts into a liquid as internal energy increases

What is the name of the state change from solid to liquid?

Melting

What happens when a liquid is heated further?

It boils into a gas as internal energy increases

What is the name of the state change from liquid to gas?

Boiling or evaporation

What happens when a gas is cooled?

It condenses into a liquid as internal energy decreases

What is the name of the state change from gas to liquid?

Condensation

What happens when a liquid is cooled further?

It freezes into a solid as internal energy continues to decrease

What is the name of the state change from liquid to solid?

Freezing

What is evaporation?

A type of vaporisation where only particles at the surface of a liquid gain enough energy to become gas

How is evaporation different from boiling?

Evaporation happens only at the surface and at temperatures below the boiling point

What is sublimation?

The state change where a solid turns directly into a gas without becoming a liquid

Give an example of a substance that undergoes sublimation.

Carbon dioxide (solid CO₂ or "dry ice")

What happens to the arrangement of particles during melting?

Particles gain energy, move more freely, and become less ordered

What happens to the arrangement of particles during boiling?

Particles gain enough energy to overcome intermolecular forces and spread far apart

What happens to the arrangement of particles during freezing?

Particles lose energy, move less, and become fixed in a regular structure

What happens to the arrangement of particles during condensation?

Particles lose energy and come closer together to form a liquid

Is mass conserved during changes of state?

Yes, mass is always conserved

Why is mass conserved in state changes?

No particles are added or removed, only rearranged

Are changes of state physical or chemical changes?

Physical changes

Why are changes of state physical changes?

Because no new substances are formed, and the change is reversible

What happens to the chemical properties of a substance during a state change?

They stay the same

What happens to the internal energy during melting or boiling?

Internal energy increases because particles gain kinetic and potential energy

What happens to internal energy during freezing or condensation?

Internal energy decreases as particles lose energy

Why do substances change state at certain temperatures?

Because that's when the particles have enough (or not enough) internal energy to overcome (or be affected by) intermolecular forces

Why is understanding internal energy important in chemistry?

It explains how and why substances change state and absorb or release energy

What stays the same during a change of state: temperature or internal energy?

Temperature stays the same during the actual state change; internal energy changes