Thermodynamics is the branch of physics concerned with energy, heat, work, and their transformations in systems. It provides a macroscopic description of matter, focusing on the relationships between measurable quantities like temperature, pressure, and volume. The field is built on four fundamental laws and has applications in diverse areas such as engines, refrigerators, chemical reactions, and the behavior of stars.
1. Fundamental Concepts
- System: The specific part of the universe we’re interested in (e.g., a car engine, a cup of coffee).
- Surroundings: Everything outside the system.
- Boundary: The separation between the system and surroundings.
- Types of Systems:
- Isolated: No exchange of energy or matter with surroundings (e.g., a perfectly insulated thermos).
- Closed: Exchange of energy but not matter (e.g., a sealed container).
- Open: Exchange of both energy and matter (e.g., a boiling pot of water).
2. Laws of Thermodynamics
These are the fundamental principles governing thermodynamic processes:
- Zeroth Law: If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other. (This establishes the concept of temperature.)
- First Law (Conservation of Energy): Energy cannot be created or destroyed, only transferred or converted from one form to another. ΔU = Q – W (change in internal energy = heat added – work done by the system)
- Second Law: The total entropy (disorder) of an isolated system always increases over time. (This explains why heat flows from hot to cold, and why some processes are irreversible.)
- Third Law: The entropy of a system approaches a constant value as its temperature approaches absolute zero.
3. Key Thermodynamic Processes
- Isothermal: Constant temperature.
- Adiabatic: No heat exchange with surroundings.
- Isobaric: Constant pressure.
- Isochoric: Constant volume.
4. Thermodynamic Properties
These are measurable quantities that describe the state of a system:
- Temperature (T): Measure of average kinetic energy of particles.
- Internal Energy (U): Total energy stored within a system.
- Entropy (S): Measure of disorder or randomness.
- Enthalpy (H): Heat content of a system at constant pressure.
- Gibbs Free Energy (G): Thermodynamic potential that can be used to predict the spontaneity of a process.
5. Applications of Thermodynamics
Thermodynamics is essential in many fields:
- Engineering: Engines, power plants, refrigeration, chemical processes.
- Physics: Understanding the behavior of gases, liquids, and solids.
- Chemistry: Predicting the direction of chemical reactions.
- Biology: Studying energy flow in living organisms.
Beyond the Basics (for JEE)
- Carnot Cycle: A theoretical engine cycle that is the most efficient possible.
- Entropy Calculations: Calculating entropy changes for various processes.
- Thermodynamic Potentials: Understanding the relationships between different thermodynamic properties.
- Statistical Mechanics: The microscopic basis of thermodynamics.