Thermodynamik

Thermodynamics, known in German as Thermodynamik, is the branch of physics that studies energy transfer in the form of heat and work and the laws that govern these processes. It seeks to understand how macroscopic properties such as temperature, pressure, volume, and composition change as energy is exchanged with surroundings.

Key concepts include state variables and state functions. The Zeroth Law introduces the concept of temperature and thermal equilibrium. The First Law expresses the conservation of energy: for any closed system, the change in internal energy equals heat added minus work done by the system. The Second Law introduces entropy and the directionality of natural processes, stating that total entropy of an isolated system cannot decrease. The Third Law implies that the absolute entropy of a perfect crystal at absolute zero is zero (up to a constant).

Thermodynamics uses state functions such as internal energy, enthalpy, entropy, and Gibbs free energy, and thermodynamic potentials to predict spontaneity and equilibrium. Equations of state relate variables like pressure, temperature, and volume. Processes are classified by paths (isothermal, isobaric, isochoric, and adiabatic).

Classical thermodynamics focuses on macroscopic properties, while statistical thermodynamics explains macroscopic behavior from microscopic states, linking to probability distributions and the Boltzmann factor. Non-equilibrium thermodynamics extends the theory to driven and time-dependent systems. Quantum thermodynamics studies energy and information at atomic scales.

Applications span heat engines, refrigerators, chemical reactions, phase transitions, and material properties. The field emerged from work of Carnot, Clausius, Kelvin, and Gibbs, and continues to evolve with simulations and advances in materials science and energy technology. In German contexts, the term Thermodynamik is widely used to denote the discipline.