Thermodynamics

  1. Definition of Thermodynamics
    Thermodynamics is the branch of physics that deals with the relationships between heat, work, temperature, and energy. It studies how energy is transferred from one form to another and how it affects matter.

  2. Applications of Thermodynamics

    • Heat Engines: Internal combustion engines, gas turbines, and steam cycles.

    • Refrigeration and Air Conditioning: Systems that move heat from a low-temperature reservoir to a high-temperature reservoir.

    • Power Plants: Converting thermal energy into mechanical or electrical work using steam turbines and nuclear reactors.

    • Chemical Engineering: Predicting the feasibility and equilibrium of chemical reactions.

  3. Two Main Types of Thermodynamics

    • Classical Thermodynamics: Focuses on the macroscopic (large-scale) behavior of systems without considering individual particles.

    • Statistical Thermodynamics: Focuses on the microscopic (molecular/atomic) level to explain macroscopic properties using statistical laws.

  4. Macroscopic vs. Microscopic Approach

    • Macroscopic Approach: Treats matter as a continuous medium (continuum). Values like pressure (P) and temperature (T) are measured directly.

    • Microscopic Approach: Considers the behavior of individual molecules. It relates the kinetic energy of particles to the overall properties of the system.

  5. The Thermodynamic System
    A Thermodynamic System is a specific quantity of matter or a region in space chosen for study. Everything outside this system is called the surroundings.

  6. The Boundary
    The boundary is the real or imaginary surface that separates the system from its surroundings. It can be fixed or movable and determines whether mass or energy can pass through.

  7. Three Types of Thermodynamic Systems

    • Open System: Both mass and energy can cross the boundary (e.g., a nozzle or turbine).

    • Closed System: Energy (heat and work) can cross the boundary, but mass cannot (e.g., a piston-cylinder without valves).

    • Isolated System: Neither mass nor energy can cross the boundary (e.g., a perfectly insulated thermos).

  8. Other Name for Open System
    An open system is often referred to as a Control Volume, and its boundary is called a control surface.

  9. Thermodynamic Property
    A property is a macroscopic characteristic (such as mass, volume, or temperature) that defines the state of a system. Properties must be independent of the path taken to reach that state.

  10. The Zeroth Law of Thermodynamics
    If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law provides the fundamental basis for temperature measurement.

  11. The First Law of Thermodynamics
    This is the law of conservation of energy. It states that energy cannot be created or destroyed, only transformed. Mathematically:
    \Delta U = Q - W
    where \Delta U is the change in internal energy, Q is heat added, and W is work done by the system.

  12. Types of Thermodynamic Properties

    • Intensive Properties: Independent of the mass or size of the system (e.g., Temperature (T), Pressure (P), Density (\rho)).

    • Extensive Properties: Dependent on the mass or size of the system (e.g., Total Mass (m), Total Volume (V), Total Energy (E)).

    • Specific Properties: Extensive properties per unit mass (e.g., Specific Volume (v = \frac{V}{m})).

  13. Entropy (S)
    Entropy is a measure of the degree of disorder or randomness in a system. According to the Second Law, the entropy of an isolated system always increases over time in an irreversible process.

  14. Common Thermodynamic Processes

    • Adiabatic: No heat transfer (Q = 0).

    • Isothermal: Constant temperature (\Delta T = 0).

    • Isobaric: Constant pressure (\Delta P = 0).

    • Isochoric (Isometric): Constant volume (\Delta V = 0).

    • Isentropic: Constant entropy; an idealized reversible adiabatic process.

    • Isenthalpic: Constant enthalpy; often seen in throttling processes.

  15. Thermodynamic Equilibrium
    A system resides in thermodynamic equilibrium if it satisfies:

    • Thermal Equilibrium: No temperature gradient.

    • Mechanical Equilibrium: No unbalanced forces or pressure gradients.

    • Chemical Equilibrium: No chemical reactions or phase changes.

    • Phase Equilibrium: The mass of each phase remains constant.

  16. State and Path Functions

    • State Functions: Properties that depend only on the current state (e.g., P, V, T, U).

    • Path Functions: Quantities that depend on the transition path between states (e.g., Heat (Q) and Work (W)).

  17. Heat Energy vs. Temperature

    • Heat (Q): The energy in transit between systems due to a temperature difference (measured in Joules).

    • Temperature (T): A measure of the average kinetic energy of molecules. While heat is a form of energy, temperature is a thermal state variable.

  18. Enthalpy (H)
    Enthalpy is a thermodynamic property defined as the sum of the internal energy and the product of pressure and volume:
    H = U + PV
    It is particularly useful in analyzing open systems and constant-pressure processes.