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First Law of Thermodynamics

Applied Science: BTEC Level 3 National Extended Diploma, topic 4.9.5

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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