Thermal Expansion of Solids, Liquids and Gases

IGCSE Coordinated Sciences: Thermal Expansion of Solids, Liquids, and Gases

Thermal Expansion of Solids, Liquids, and Gases

Describe qualitatively the thermal expansion of solids, liquids, and gases.
Solids:
A solid gains kinetic energy and starts to vibrate more vigorously when thermal or heat energy is applied to it.
As a result, the solid expands slightly in all directions.
Liquids:
When a liquid is heated, the volume of the liquid increases as a result of the molecules having more kinetic energy. The liquid expands to take up more volume in its container.

Gases:
Understanding the thermal expansion of gases depends on the circumstances:

If a gas is kept in a container of constant volume, like a canister, and is then heated up, the gas does not expand. This is because gases occupy the entire volume of their container. Instead, the pressure inside the container increases as the molecules have more kinetic energy and collide with the container walls more often.
On the other hand, if a gas is kept at a constant pressure inside its container, the gas expands when heat is applied, and the volume of the container increases proportionally to the change in temperature.

Explain in terms of motion and arrangement of molecules the relative order of magnitude of the expansion of solids, liquids, and gases.
Expansion of a substance: gas > liquid > solid
When a fixed mass of a substance is heated, it expands the most as a gas, followed by a liquid, and finally as a solid.

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This is because the intermolecular forces in a gas are very weak compared to the other two states of matter.
In a solid, the intermolecular forces that hold it together are much stronger, and the molecules are arranged in an organized manner.

Identify and explain some of the everyday applications and consequences of thermal expansion.
Solids:

Thermal expansion can be used to fit metal axles onto wheels. The metal axle is first cooled to contract and then placed through the wheel's hole so that when it warms up and expands, it forms a tight grip on the wheel.
Train tracks are built with gaps between each section to accommodate thermal expansion. This prevents warping of the tracks under hot weather when they expand and exert pressure on each other.
Describe qualitatively the effect of a change of temperature on the volume of a gas at constant pressure.
The equation that links pressure, volume, and temperature for a fixed mass of gas is:
(P1 * V1) / T1 = (P2 * V2) / T2
In essence, the pressure and volume of a fixed mass of gas are proportional to its temperature in Kelvin.
However, if pressure (P) is kept constant, then the equation becomes:
V1 / T1 = V2 / T2
Where the volume of the gas is directly proportional to its temperature in Kelvin.
This is known as Charles' Law.