Thermodynamics is a branch of physics that deals with the relationships between heat, work, temperature, and energy. It provides a framework for understanding how energy is transferred and transformed in physical systems. Here’s an overview:
Key Concepts
- System and Surroundings:
- System: The part of the universe being studied (e.g., a gas in a piston, a steam engine).
- Surroundings: Everything outside the system.
- State Variables:
- Properties like temperature (T), pressure (P), volume (V), and internal energy (U) that describe the system’s state.
- Energy:
- Energy exists in various forms (e.g., heat, work, potential energy) and is conserved.
- Heat (Q):
- Energy transfer due to temperature difference.
- Work (W):
- Energy transfer when a force moves something in the surroundings.
Laws of Thermodynamics
1st Law: Law of Energy Conservation
The total energy of an isolated system is constant. Energy can be transferred as heat or work, but it cannot be created or destroyed.ΔU=Q−WΔU=Q−W
- ΔUΔU: Change in internal energy
- QQ: Heat added to the system
- WW: Work done by the system on the surroundings
2nd Law: Entropy and Irreversibility
Entropy (SS) measures the disorder or randomness in a system. The second law states:
- Entropy in an isolated system never decreases; it increases or remains constant in reversible processes.
- Heat cannot spontaneously flow from a colder body to a hotter body without external work.
This law explains the direction of natural processes and the efficiency limits of engines.
3rd Law: Absolute Zero
As the temperature of a system approaches absolute zero (0 Kelvin), the entropy of a perfect crystal approaches a constant minimum. Absolute zero is the theoretical temperature where all motion stops.
Thermodynamic Processes
- Isothermal (TT constant): Heat exchange occurs, but internal energy remains unchanged.Q=WQ=W
- Adiabatic (No heat transfer): Energy is transferred only as work.ΔU=−WΔU=−W
- Isochoric (VV constant): No work is done, as the volume doesn’t change.ΔU=QΔU=Q
- Isobaric (PP constant): Pressure remains constant while heat and work are exchanged.
Applications of Thermodynamics
- Engines: Efficiency and operation of heat engines (e.g., car engines, steam turbines).
- Refrigeration: Heat transfer for cooling systems.
- Chemical Reactions: Energy changes and equilibrium in reactions.
- Meteorology: Atmospheric energy flow.
Thermodynamics bridges the microscopic behavior of molecules with macroscopic phenomena, making it fundamental to science and engineering.