Introduction to Thermodynamics

Introduction to Thermodynamics

• Thermodynamics is the branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation.
• It describes macroscopic properties of materials in terms of microscopic molecular properties.
• The core of thermodynamics is based on laws, principles that govern energy transfer and transformations, and how they affect systems.

The Zeroth Law of Thermodynamics

• The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
• This law forms the basis for the definition of temperature.

The First Law of Thermodynamics

• The first law of thermodynamics is a statement of the conservation of energy.
• It states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.
• Mathematically, it can be expressed as ΔU = Q − W.

The Second Law of Thermodynamics

• The second law of thermodynamics states that the total entropy of an isolated system can only increase over time, or remain constant in ideal cases.
• This law explains the irreversibility of many natural processes.
• Commonly expressed in terms of heat engines and refrigerators and the concept of entropy increase.
• The entropy of an isolated system can never decrease.

The Third Law of Thermodynamics

• The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is zero.
• This law defines a zero point for entropy.
• It means that as temperature approaches absolute zero, the entropy of a system approaches a minimum value.

Concepts and Principles

• Internal Energy (U): The total energy of a system, including kinetic and potential energies of constituent particles.
• Heat (Q): The energy transferred between a system and its surroundings due to a temperature difference.
• Work (W): The energy transferred to or from a system by the application of a force.
• Entropy (S): A measure of the disorder or randomness of a system.
• Temperature (T): A measure of the average kinetic energy of the particles in a system.
• Enthalpy (H): A thermodynamic potential that measures the total heat content of a system at constant pressure.
• Adiabatic processes: Processes where no heat is exchanged with the surroundings.
• Isothermal processes: Processes where the temperature remains constant.
• Isobaric processes: Processes where the pressure remains constant.
• Isochoric processes: Processes where the volume remains constant.

Applications of Thermodynamics

• Engineering: Designing heat engines, refrigerators, and power plants.
• Chemistry: Understanding chemical reactions and phase transitions.
• Biology: Modeling biological systems.
• Meteorology: Modelling weather patterns.

Thermodynamic Cycles

• Carnot Cycle: A theoretical cycle that represents the most efficient possible heat engine.
• Rankine Cycle: A cycle used in power plants, that converts heat into work.
• Otto Cycle: A cycle in internal combustion engines.
• Diesel Cycle: A cycle in diesel engines with different compression and combustion characteristics, compared to Otto Cycles.
• Understanding these cycles helps determine efficiency limits and fundamental operating principles of devices that convert heat to mechanical work.