Thermodynamics: Principles, Laws, and Applications

Thermodynamic Systems and Surroundings

A thermodynamic system is a precisely defined region of the universe selected for study, while everything outside it is called the surroundings. The system may exchange energy, matter, or both with its surroundings, depending on its boundaries and classification. Energy can cross the boundary as heat, work, or through the transfer of matter, while the system's state is described by macroscopic properties such as temperature, pressure, volume, internal energy, and entropy. The interaction between a system and its surroundings determines how the system changes and whether it can reach equilibrium. Boundaries may be real or imaginary, fixed or movable, and permeable or impermeable. Thermodynamic reservoirs are special surroundings large enough that contact with a system does not significantly change their own state; examples include the atmosphere as a pressure reservoir and the ocean as a temperature reservoir. These concepts provide the foundation for analyzing engines, chemical reactions, phase changes, and other thermodynamic processes.

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Energy, Heat, and Work

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