Thermodynamica

Thermodynamica is the branch of physics that studies the relationships between heat, work, temperature, and energy in physical systems. It describes how energy is transferred and transformed as matter and radiation interact, and it applies to engines, chemical reactions, phase changes, and many natural processes.

Historically, thermodynamics emerged in the 19th century through the work of scientists such as Carnot, Clausius, Kelvin, and Boltzmann. Their development established general principles for describing energy conversion and the direction of spontaneous processes.

The field is organized around four laws. The zeroth law defines thermal equilibrium and the concept of temperature. The first law expresses the conservation of energy: dU = δQ − δW, relating heat added to a system and the work it performs. The second law introduces entropy and sets a direction to spontaneous change; for any process, ΔS ≥ ∫ δQ_rev / T, with equality for reversible paths. The third law states that as temperature approaches absolute zero, the entropy of a perfect crystal approaches a minimum value.

Key concepts include state functions such as internal energy U, enthalpy H, entropy S, and Gibbs free energy G. For simple compressible systems, the differential form dU = δQ − δW and δW = P dV apply. Reversible heat transfer satisfies δQ_rev = T dS, and many practical problems are solved in terms of these functions.

Thermodynamics underpins many disciplines, including mechanical and chemical engineering, materials science, meteorology, and physical chemistry. It complements statistical thermodynamics, which explains macroscopic behavior from microscopic states using ensembles and probability.