SITEMAP   School-college Physics Notes: Thermal energy 4.10 Particle models

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Thermal energy & particle theory: 4.10 Increasing the energy store of gas - work done and temperature effects on heating the gas

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4.10 Increasing the energy store of gas - work done and temperature effects

• Increasing the energy store of gas by compressing it

• When you pump air into a bicycle tyre as energetically as you can, you can detect a rise in temperature, particularly near the pump connection point. So, why the increase in temperature of the gas?

• When you compress a gas by applying a mechanical force you do work of compression on the gas.

• This work in compressing the gas increases the internal energy and increases the temperature - increasing the thermal energy store - the kinetic energy store is increased.

• You have to do work on the gas because as you compress the air in the pump, the pressure rises as the force of the particle impacts acts against you, so you have to do work against this increased force/unit area (pressure) to get the air into the tyre.

• By doing work on a gas in this way the increase in the internal energy store of the gas ends up as increased kinetic energy of the particles, which causes the temperature rise of the air, tyre and pump.

• This effect is used in refrigerators where a refrigerant gas is compressed to release energy in a closed system - this thermal energy is obtained from the refrigerant liquid evaporating by absorbing the latent heat of vaporisation from the interior of the fridge-freezer.

• Check out the sections on latent heat, but know that ....

• If you compress a gas, decreasing its volume, you increase its internal energy, increasing the average kinetic energy of the particles and the gas gets warmer with an increase in its temperature.

• If you expand a gas, increasing its volume, you decrease its internal energy, decreasing the average kinetic energy of the particles, the gas cools as the temperature is reduced.

• These effects are due to the increase or decrease in the intermolecular force between particles.

• Increasing the energy store of gas by heating it

• Increasing the temperature of a gas increases its kinetic thermal energy store.

• Increasing the temperature increases the average speed of particles and their kinetic energy.

• In fact, the temperature of a gas is proportional to the average kinetic energy of the particles.

• This means on heating a gas in a sealed container there are more particle impacts and more forceful impacts on the surface per unit area.

• Therefore heating a gas at constant volume increases the gas pressure.

• Conversely if you cool a sealed cylinder of gas, the pressure decreases.

• More on gases and more on gas calculations (both in the GCSE level chemistry notes).

Keywords, phrases and learning objectives for particle models and increasing the internal energy of gas

Know and be able to explain how the energy store of gas is increased by doing work on it in compression or increasing the gas temperature.

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