Changes in Internal Energy
We cannot measure the internal energy in a system, we can only determine the change in internal energy, E, that accompanies a change in the system.
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:
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|