Explain how doing work on an enclosed gas, such as in a bicycle pump, increases its temperature.
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GCSE Physics Revision
Learn it. Recall it. Revise it.
GCSE Physics revision
Increasing the pressure of a gas (physics only) (HT only)
Particle model and pressure
Your specification
AQA student objectives
Learning pathway
All · Most · Some
Apply the relationship between work done on a gas and its temperature change to explain an example.
Analyse how compressing an enclosed gas transfers energy and affects its temperature.
Revision summary
Key knowledge
Read on screen, then print for Cornell-style active revision.
How Volume Affects Pressure
- When volume increases, molecules are more spread out and must travel greater distances before hitting the walls, resulting in fewer collisions per unit area and lower pressure.
- When volume decreases, molecules are closer together and travel shorter distances, leading to more collisions per unit area and higher pressure.
- This inverse relationship between pressure and volume applies to a fixed amount of gas at constant temperature.
The Pressure–Volume Law (Boyle's Law)
- For a fixed mass of gas at constant temperature, pressure multiplied by volume is always a constant: pV = constant.
- Pressure (p) is measured in Pascals (Pa) and volume (V) is measured in metres cubed (m³).
- As pressure increases, volume decreases proportionally so that the product pV remains unchanged.
- This equation is provided on the GCSE equation sheet, so it does not need to be memorised but must be selected and applied correctly.
Using the Pressure–Volume Equation: Example 1
- To find the constant, multiply the initial pressure by the initial volume: 100{,}000 × 10 = 1{,}000{,}000 (Pa·cm³).
- Rearranging for the new volume gives V_2 = pV / p_2 = frac{1{,}000{,}000} {120{,}000} approx 8.3 cm³, confirming that increasing pressure reduces volume.
- It is important to keep units consistent throughout the calculation — if the volume is given in cm³, there is no need to convert to m³ if the answer is also required in cm³.
Using the Pressure–Volume Equation: Example 2 (Standard Form)
- The constant is found by calculating 3.2 × 10^5 × 6.75 = 2.16 × 10^6 text{ Pa·cm}³.
- Rearranging gives V_2 = 2.16 × 10^6 / 3.6 × 10^5 = 6 cm³, showing that standard form values are handled in exactly the same way.
Rapid Compression and Temperature Rise
- When a gas is rapidly compressed, work is done on the gas by the applied force, transferring energy to the gas.
- This transferred energy increases the internal energy of the gas, raising the average kinetic energy of its particles.
- Because temperature is a measure of the average kinetic energy of particles, an increase in average kinetic energy means an increase in temperature.
- A common example is a bicycle pump: compressing air rapidly into a tyre causes a noticeable rise in temperature.
Why Slow Compression May Not Raise Temperature
- During slow compression, work is still done on the gas, but energy may be transferred to the surroundings at the same rate as it is gained.
- Because energy is lost as quickly as it is gained, the internal energy does not build up and the temperature does not rise significantly.
Investigating Pressure and Volume Experimentally
- A syringe or pump apparatus can be used to apply different pressures to a trapped gas while measuring the corresponding volume.
- Readings of pressure (from a pressure gauge) and volume (from a volume scale) can be recorded and used to verify that pV remains constant.
- This type of investigation provides experimental evidence for the pressure–volume relationship in a closed gas system.
Key Vocabulary Summary
- Pressure is defined as force per unit area and is measured in Pascals (Pa).
- A closed container means no gas enters or leaves, so the number of molecules remains fixed.
- Internal energy is the total kinetic and potential energy of all the particles in a substance.
- The average kinetic energy of particles in a gas is directly related to its temperature.