Heating Solids, Liquids & Gases

D. Crowley, 2008

Heating Solids, Liquids & Gases

To understand what happens to solids, liquids and gases when they are heated

Wednesday, April 19, 2023

Particle Model

What is the particle model, and what are the key characteristics of a solid, liquid and gas?

The particle theory states that all things are made of tiny pieces, called particles

Solids, liquids and gasses all have different arrangements of these particles, giving them their special properties…

Solids Liquids Gases

Particle ModelSolids Liquids Gases

State Solid Liquid Gas

Arrangement of particles

Movement of particles

Close togetherRegular pattern

Close togetherRandom

Far apartRandom

Vibrate on the spot

Move around each other

Move quickly in all directions

Heat

What happens to these particles when they are heated (given thermal energy)?

What happens to these particles when they are cooled?

When particles are given more thermal energy (heat) they take up more room and expand, and when this is taken away they take up less room and contract

How could you prove this?

Heating

Look at the ball and ring - the ball can pass through the ring easily

But… when the ball is heated (given thermal energy) it cannot pass through the ring!

However, if we heat them both, the ball passes through the ring

This shows that as an object is given more thermal energy its particles take up more room

Cooling

When the ball is allowed to cool, it suddenly passes through the hoop again

Also, a heated glass rod will shatter if placed into iced water

This is because the glass rod is cooled so quickly parts of it contract at such a rate that stresses cause it to shatter

Expansion & Contraction

What happened when we heated the ball?

Substances expand (get bigger) when they are heated up

What happened when we rapidly cooled the glass?

Substances contract (get smaller) when they are cooled

Expansion & Contraction Substances expand (get bigger) when they are heated up

The particles stay the same (the number of particles + their size is the same) But they take up more room!

Substances expand (get bigger) when they are heated up

The particles stay the same (the number of particles + their size is the same) But they take up more room!

When heated: - Solids - particles vibrate more and

take up more room

Liquids - move around each other more quickly and take up more room

Gases - move more quickly in all directions, and take up more room

When heated: - Solids - particles vibrate more and

take up more room

Liquids - move around each other more quickly and take up more room

Gases - move more quickly in all directions, and take up more room

Substances contract (get smaller) when they are cooled down

When we cool objects, the number of particles and their size remains the same, they just take up less room!

Substances contract (get smaller) when they are cooled down

When we cool objects, the number of particles and their size remains the same, they just take up less room!

Expansion & Contraction

Look at the example of the cylinder and the hole

Substances expand when they are heated

Substances contract when they are cooled

Role play expansion & contraction…Role play expansion & contraction…

Problems & Uses

Expansion of substances can be both useful, and cause problems for designers and engineers - can you think of any?

Problem - bridges expand in the summer, and need special joints to stop them bending out of shape

Concorde (the supersonic plane) expanded when it was going at very high speed by ~30cm!

At very high speed friction causes a great deal of heat - this expands the plane in a variety of areas

Expansion joint in a bridge

Thermometers use liquids which expand when they get hotter, and contract when the get colder - very useful for us to measure heat!

Temperature & Thermal Energy How can we model the difference between high temperature, and

high thermal energy?

Thermal energy (heat) is the energy that a substance possesses due to the kinetic energy of its particles

Temperature is a measure of the average kinetic energy of the molecules of a substance

A few gas particles – this can be a high temperature (average kinetic energy) but

the thermal energy (heat) it has is small as there are not that many particles

Many gas particles – this can be a high temperature (average kinetic energy) but the thermal energy (heat) it has is much larger as there are many more particles

Accident

Imagine a spoonful of 100oC water and a tank filled with water, also at 100oC

Which would you rather have spilled on you?

The water in the tank can transfer much more heat, despite the fact that its temperature is no higher that the water in the spoon