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First Law of Thermodynamics

Physics: AQA A Level, topic 11.2.1

The First Law of Thermodynamics

If we are interested in how heat transfer is converted into doing work, then the conservation of energy principle is important.

Calculation

Calculation

  • The equation for the first law of thermodynamics is:
  • The change in internal energy = the net heat transfer into the system - the net work done by the system.
  • ΔU=Q−W{\Delta}U=Q-W
  • Where U is the internal energy, Q is the heat and W is the work done by the gas.
Work done

Work done

  • If the work is done by the gas the work done is positive, this is when a gas expands.
  • If the work done is on the gas the work done is negative, this is when a gas is compressed.
  • If the volume does not change there is no work done.

Test yourself on First Law of Thermodynamics

  • What is the correct form of the first law of thermodynamics?

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