Physics Thermal Expansion and Change of State

What is thermal expansion?

Thermal expansion is the expansion of a substance when heated

Why does thermal expansion occur?

Thermal expansion occurs as when heated, molecules start to move around faster due to their increase of kinetic energy, and they collide with one another pushing each other apart. The separation of the molecules make the substance bigger

Uses of Bimetallic strip

A bimetallic strip consists of two metals that expand at different rates. Temperature activated switches use a bimetallic strip to close circuits.

Use of shrink-fitting axles

An axle is cooled down, decreasing its size, and the axle is put into gears. The axle then warms up and expands, and it is stuck in the gears tightly.

Use of expansion joints

In bridges and railway tracks, the materials used often get very hot and expand. Expansion joints are gaps in between where pieces meet, and used to allow the structure to expand and contract without causing any damage

Why do solids expand the least

Solids have the strongest forces between their particles, so when their particles gain energy, they can’t move very far apart.

Why do liquids expand more?

The forces between liquid’s particles are weaker than in a solid, so the particles can move further apart

Why do gases expand the most?

The forces between the particles in a gas are almost non-existent, so they are able to move the furthest when they gain energy through heating

Why does the temperature during boiling and melting of a substance not change?

The heat that is being supplied is being used up in changing state of matter by overcoming intermolecular forces of attraction, instead of increasing the particles kinetic energy

What is condensation?

Condensation is when particles in a gas lose kinetic energy and move more slowly. This means they no longer have enough energy to overcome the intermolecular forces of attraction and get closer together and have enough energy to flow over one another, becoming a liquid

What is solidification (freezing)

Solidification is when particles in a liquid lose kinetic energy and no longer have enough energy to overcome the intermolecular forces of attraction. The particles get closer together and have enough energy to vibrate about their fixed position, becoming a solid.

What is evaporation?

Evaporation is when more energetic molecules moving near the surface of the liquid have enough energy to overcome the attractive forces in the liquid and are travelling towards the surface, and escape

Why does evaporation cool liquids down?

As the particles with the most kinetic energy escape, the average kinetic energy in the liquid decreases and therefore the temperature decreases

Why does surface area increase the rate of evaporation?

The larger the area of the liquid, the more particles will be near the surface and have enough energy to escape

Why does air movement over the surface increase the rate of evaporation?

If air is moving over the liquid’s surface, the particles that escape won’t be able to drop back in as they will be carried away

Why does temperature increase the rate of evaporation?

The higher the temperature, the higher the average kinetic energy of the liquid, which means more particles have enough energy to escape

Difference between boiling and evaporation

• Boiling happens at the boiling point of a substance - evaporation happens at any temperature below the boiling point

• Boiling happens throughout the liquid - evaporation happen from the surface

Why does an object cool when it comes in contact with an evaporating liquid?

As the liquid cools, the energy from the object will be transferred to the liquid, and as energy is being transferred away, the object cools down