Expansion and Contraction in Solids, Liquids and Gases

Learning Objective

In this lesson we will learn how temperature changes affect the volume of solids, liquids and gases.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe the relationship between heat energy, movement of particles and the volume of a substance.

  • Use the particle model to explain expansion and contraction of solids, liquids and gases.

  • Compare expansion and contraction in solids, liquids and gases.

  • Describe some practical and safety considerations associated with the expansion and contraction of matter.

 

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Introduction

  • We have seen that changes in heat energy affect the movement of particles, even if there is no change in state.
    An increase in heat energy make the particles move faster.
    A decrease in heat energy makes the particles move slower.
  • Changes in the rate of particle movement result in changes in the volume occupied by that substance.

 
heat energy particle movement expansion

Heat energy causes particles to move more, resulting in expansion of a substance.

 

Expansion and Contraction

  • When the movement of particles speeds up, there is an increase in the space between them.
    An increase in the space between particles means that the substance expands.
    In other words, there is an increase in the volume (space) it occupies.
  • When the movement of particles slows down, there is a decrease in the space between them.
    A decrease in the space between particles means that the substance contracts.
    In other words, there is a decrease in the volume (space) it occupies.
  • This general relationship between particle movement and volume is the same for solids, liquids and gases.
    However, the extent to which a substances expands or contracts varies between the different states of matter.

 
hot air balloon expansion

Heating air causes it to expand, which inflates this hot air balloon.

(Image: ddouk, Pixabay)

 

Expansion and Contraction in Solids

  • When solids are heated, their particles vibrate more rapidly, pushing each other apart slightly, causing the solid to expand.
  • The amount of increase in volume depends on the type of solid.
    For example, increasing the temperature of a 1 metre section of glass by 100 °C will cause it to expand by 9 mm; concrete and steel will expand by 11 mm and aluminium will expand by 25 mm.
  • Similarly, decreases in temperature cause solids to contract by varying degrees.
  • Even though the amount of expansion and contraction in solids may seem quite small, it can have serious implications in certain situations, such as the construction industry.
    For example, power lines need to be hung from poles at the correct tension (tightness). If the tension is too tight, the power lines will contract and break in cold weather; if the tension is too loose, they will expand and hang too close the ground in hot weather.

 
expansion contraction metal wire power lines

The tension of these power lines must allow for expansion and contraction of the metal wires.

(Image: Silberfuchs, Pixabay)

 

Expansion and Contraction in Liquids

  • When liquids are heated, their particles move around more, pushing each other apart slightly, causing the liquid to expand.
  • As with solids, the amount of increase in volume depends on the type of liquid, but in general, liquids expand more than solids when heated.
    This is because the particles in liquids are not held in a fixed arrangement, as they are in solids, so this increased freedom of movement results in greater expansion.
  • As with solids, the expansion and contraction of liquids needs to be allowed for in certain situations.
    For example, car radiators are connected to an overflow tank to allow for the expansion of coolant as it is heated by the engine.
  • There are also practical applications of thermal expansion of liquids, such as thermometers.
    Since liquids expand and contract by predictable amounts based on their temperature, the change in volume of the alcohol in a thermometer tube can be used to give a measure of the temperature.

 
thermometer thermal expansion contraction liquid

The liquid in thermometers expands and contracts, depending on the temperature.

(Image: PublicDomainPictures, Pixabay)

 

Expansion and Contraction in Gases

  • When gases are heated, their particles move with greater speed and energy, resulting in greater space between them, causing the gas to expand.
  • Gases expand much more than solids and liquids when heated.
    This is because the particles in gases are not held closely together, as they are in solids and liquids, but are instead free to move in all directions.
  • When referring to gases that are in an enclosed container with a fixed size, we don’t refer to changes in volume.
    This is because at any temperature the gas particles will fill the whole container.
    Instead we refer to changes in pressure experienced by the container.
    Pressure is the result of the particles colliding with the walls of the container.
  • The higher the temperature, the greater the speed of the gas particles and the greater the energy of the collisions with the container.
    In other words, an increase in the temperature of a gas will result in an increase in pressure inside a container.
  • Since gases respond significantly to changes in temperature, there are many safety considerations when handling gases in containers, especially since they are often already stored under high pressure.
    For example, it is extremely dangerous to heat containers that store gas, such as gas cylinders or aerosol cans, due to the risk of explosion.

 
gas heat expansion cylinders

Gas cylinders should never be heated.

(Image: Public Domain Pictures)

 

Summary

  • When a substance absorbs or loses heat energy, the movement of its particles is affected, which causes its volume to change.
  • Solids, liquids and gases all expand when heated, due to the increased movement of their particles.
  • Solids, liquids and gases all contract when cooled, due to the decreased movement of their particles.
  • Temperature changes affect the volume of gases the most and the volume of solids the least.
  • There are many practical and safety considerations associated with the expansion and contraction of matter due to temperature changes.

 
hot air balloon air expansion

(Image: TCB, Pixabay)

 

(Header image: PellissierJP, Pixabay)

 

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