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3: First Law of Thermodynamics

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    • 3.1: Calculation of Internal Energy Changes
      The internal energy (U) of a system is a thermodynamic state function defined as the property of a system that can be either transferred or converted.
    • 3.2: The First Law of Thermodynamics
      We finally come to a working definition of the first law. If we take an isolated system—i.e., a system that does not exchange heat nor mass with its surroundings—its internal energy is conserved. If the internal energy is conserved, dU=0 .
    • 3.3: Reversible and Irreversible Processes
      Let’s now consider the cycle in Figure 3.3.1. The process in this case starts from state 1 (system at P1V1), expands to state 2 (system at P2V2), and compresses back to state 1 (system back to P1V1).

    This page titled 3: First Law of Thermodynamics was last modified on Tue, 11 Aug 2026 22:14:19 GMT and is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Roberto Peverati via source content that was edited to the style and standards of the LibreTexts platform.