Article
Article
Internal energy
Article By:
Bender, Paul J. Formerly, Department of Chemistry, University of Wisconsin, Madison, Wisconsin.
Last reviewed:August 2020
DOI:https://doi.org/10.1036/1097-8542.349600
A characteristic property of the state of a thermodynamic system, introduced in the first law of thermodynamics. For a static, closed system (no bulk motion, no transfer of matter across its boundaries), the change ΔU in internal energy for a process is equal to the heat Q absorbed by the system from its surroundings minus the work W done by the system on its surroundings. Only a change in internal energy can be measured, not its value for any single state. For a given process, the change in internal energy is fixed by the initial and final states and is independent of the path by which the change in state is accomplished.
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