IGCSE Coordinated Sciences: Thermal expansion of solids, liquids and gases
Thermal expansion of solids, liquids and gases
1. Describe qualitatively the thermal expansion of solids, liquids and gases.
Solids:
When thermal/heat energy is applied to a solid, the molecules of the solid gain kinetic energy and begin to vibrate more vigorously.
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 more of the volume of its container.
Gas:
The thermal expansion of a gas is slightly trickier depending on the situation:
If the gas is kept in a container of a constant volume, like a canister, and is then heated up, the gas does not expand. This is because gases take up the entire volume of its container. Instead, the pressure inside the container increases since the molecules have more kinetic energy and therefore collide with the walls of the container more often.
On the other hand, if the gas is kept at a constant pressure inside its container, as the gas expands when heat is applied, the volume of the container will increase proportionally to the change in temperature.
2.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 up, it will expand the most as a gas followed by as a liquid and lastly as a solid.
This is because the molecules in a gas have very weak intermolecular forces that keep them together as compared to the other two states of matter.
If we look at a solid, the intermolecular forces that keep it together are much more stronger. The molecules in a solid are arranged in a organized manner.
3. Identify and explain some of the everyday applications and consequences of thermal expansion.
Solids:
- Thermal expansion could be used to fit metal axles onto wheels. The metal axle is first cooled so that it contracts. It is then placed through the hole of wheel 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 of the track so that when it expands under hot weather, the train tracks won’t warp as a result of the pressure of being squished together.
4. Describe qualitatively the effect of a change of temperature on the volume of a gas at constant pressure.
Equation that links pressure, volume and temperature for a fixed mass of gas:
(P1*V1) / T1 = (P2*V2) / T2
In essence, the pressure and volume of a fixed mass of gas is proportional to its temperature in Kelvin
However, if P is kept constant, then our equation becomes:
V1 / T1 = V2 / T2
Where the volume of the gas is directly proportional to its temperature in Kelvin.
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