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Non-Flow Processes

Physics: AQA A Level, topic 11.2.2

Isothermal and adiabatic processes

If a gas expands at a constant temperature it is isothermal, if it expands with no heat transfer it is adiabatic.

Isothermal

Isothermal

  • If a gas expands at a constant temperature it is isothermal.
  • An isothermal line on a pressure-volume graph is a curved line of constant temperature.
  • The product of the pressure and the volume is a constant.
  • pV=constantpV=constant
Adiabatic

Adiabatic

  • If a gas expands with no heat transfer it is adiabatic.
  • This means the first law becomes:
  • ΔU=W{\Delta}U= W
  • The condition for an adiabatic expansion is:
  • pVγ=constantpV^{\gamma}= constant
  • Where γ\gamma is a constant.

Constant pressure and volume

Gasses can expand or be compressed under constant pressure or volume.

Constant pressure

Constant pressure

  • At constant pressure, the work done by a gas is given by the pressure multiplied by the change in volume. The equation for work done is:
  • Work done = pressure x change in volume
  • W=pΔVW=p{\Delta}V
  • Work done is measured in Joules.
Constant volume

Constant volume

  • If a gas is acted on at a constant volume no work is done as ΔV{\Delta}V = 0.

Test yourself on Non-Flow Processes

  • Which of these statements about non-flow processes are true?

  • On a p-V graph, what do adiabatic and isothermal lines look like?

  • At constant pressure what is the equation for the work done by a gas?

  • Work done is measured in what unit?

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