Internal Energy, Heat, and Work

Changes in Internal Energy

We cannot measure the internal energy in a system, we can only determine the change in internal energy, DeltaE, that accompanies a change in the system.

Delta E equals E final minus E initial

The change in internal energy that accompanies the transfer of heat, q, or work, w, into or out of a system can be calculated using the following equation:

Equation for calculation of delta E

Note the value of heat and work as they are transferred into or out of a system.

Reduces E Increases E
q < 0 (q negative), heat lost q > 0 (q positive), heat gained
w < 0 (w negative), work done by system w > 0 (w positive), work done on system


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