termodynami

Thermodynamics is the branch of physical science that studies energy interactions and the transfer of heat and work within physical systems. It applies to gases, liquids, solids, and chemical reactions, and underpins technologies from heat engines to refrigerators and energy systems.

The field rests on four fundamental laws. The Zeroth Law establishes the concept of temperature and thermal equilibrium between systems. The First Law expresses the conservation of energy: the change in internal energy ΔU of a system equals the heat added to the system Q minus the work done by the system W (ΔU = Q − W). The Second Law introduces entropy and the directionality of processes, limiting the efficiency of real engines and defining the Carnot efficiency. The Third Law states that the entropy of a perfect crystal approaches zero as temperature approaches absolute zero.

A system is described by state variables such as energy, temperature, pressure, and volume. Processes may be isothermal, isobaric, isochoric, or adiabatic. Systems can be closed, open, or isolated, and the interactions with surroundings determine the amounts of heat transfer and work performed.

Historically associated with figures like Sadi Carnot, Rudolf Clausius, and James Joule, thermodynamics has become essential in engineering, chemistry, and physics. Practical applications include heat engines, power plants, refrigeration cycles, chemical reactions, and energy management in industrial processes.