Fundamental Concepts of Thermodynamics

Fundamental Concepts of Thermodynamics

• Thermodynamics studies heat, work, temperature, and their connections to energy, entropy, and other system properties.
• The four laws of thermodynamics explain the fundamental principles of these connections.

The Zeroth Law of Thermodynamics

• Defines thermal equilibrium.
• If two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other.
• Establishes temperature as a measurable property.

The First Law of Thermodynamics

• Energy cannot be created or destroyed, only transformed.
• Change in a system's internal energy equals heat added minus work done by the system (ΔU = Q - W).

The Second Law of Thermodynamics

• Heat does not spontaneously flow from cold to hot.
• Defines entropy, a measure of disorder or randomness.
• Total entropy of an isolated system always increases over time.
• Has equivalent statements (Kelvin-Planck, Clausius) regarding impossible thermal processes.

The Third Law of Thermodynamics

• Entropy of a perfect crystal at absolute zero is zero.
• Reaching absolute zero is impossible.
• Sets a lower bound for achievable entropy.

Thermodynamic Systems and Processes

• A thermodynamic system is a section of the universe being studied.
• Surroundings are the rest of the universe.
• Boundaries (real or imaginary) separate the system from its surroundings.
• Heat (energy transfer) occurs due to temperature differences.

Types of Thermodynamic Processes

• Isothermal: Constant temperature.
• Adiabatic: No heat transfer.
• Isobaric: Constant pressure.
• Isochoric: Constant volume.
• Cyclic: Returns to its initial state.

Thermodynamic Properties

• Internal energy (U): Sum of all microscopic energies in the system.
• Enthalpy (H): Measures total heat content at constant pressure.
• Entropy (S): Measures disorder or randomness.
• Gibbs Free Energy (G): Measures maximum reversible work at constant temperature and pressure.

Applications of Thermodynamics

• Power generation: Converting thermal to mechanical energy (steam turbines, engines).
• Refrigeration/Air Conditioning: Transferring heat from cold to hot reservoirs.
• Chemical engineering: Designing efficient processes.
• Material science: Understanding phase changes and material behavior.
• Astrophysics: Modeling stellar evolution and atmospheres.

Key Concepts in Heat and Temperature

• Temperature: Measures average kinetic energy of particles.
• Heat: Transfer of thermal energy due to temperature differences.
• Specific heat capacity: Heat needed to raise 1 kg of substance by 1 °C or 1 K.

Equations and Relations

• Various equations relate thermodynamic properties for calculations.

Ideal Gas Law

• Ideal gases are simplified models in thermodynamics.
• Relates pressure, volume, temperature, and moles of a gas (PV = nRT).

Real Gases

• Real gases deviate from the ideal gas law at high pressures and low temperatures due to intermolecular forces and particle volume.
• Van der Waals equation is a more accurate model.

Entropy and Statistical Mechanics

• Entropy links to the microscopic system state.
• Statistical mechanics connects macroscopic properties with particle configurations.