Introduction to Thermodynamics

Introduction to Thermodynamics

• Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relationship to energy, entropy, and the properties of matter and radiation.
• Key concept is that energy can change from one form to another, but it cannot be created nor destroyed.
• It describes macroscopic properties of matter without going into microscopic details of atoms or molecules.

Laws of Thermodynamics

• Zeroth Law of Thermodynamics: If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. This establishes the concept of temperature.
• First Law of Thermodynamics: Energy can be transferred and changed from one form to another but cannot be created or destroyed. This law deals with conservation of energy and is often expressed as ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.
• Second Law of Thermodynamics: The total entropy of an isolated system can never decrease over time. A spontaneous process increases the total entropy of the universe.
• Third Law of Thermodynamics: As a system approaches absolute zero (0 Kelvin), its entropy approaches a constant minimum value. This is related to the unattainability of absolute zero.

Thermodynamic Systems

• Open System: Matter and energy can be exchanged with the surroundings.
• Closed System: Energy can be exchanged with the surroundings, but matter cannot.
• Isolated System: Neither matter nor energy can be exchanged with the surroundings.

Key Concepts and Definitions

• Internal Energy (U): The total energy of the particles within a system.
• Heat (Q): The transfer of thermal energy between a system and its surroundings due to a temperature difference.
• Work (W): Energy transferred to or from a system by a force causing a displacement.
• Entropy (S): A measure of the disorder or randomness of a system. A system with high entropy is more disordered, while low entropy systems are highly organized.
• Temperature (T): A measure of the average kinetic energy of the particles in the system and is related to the thermal energy.
• Adiabatic Process: A process that occurs without heat transfer between the system and its surroundings.
• Isothermal Process: A process that occurs at a constant temperature.
• Isobaric Process: A process that occurs at a constant pressure.
• Isochoric Process: A process that occurs at a constant volume.
• Specific Heat Capacity (C): The amount of heat energy required to raise the temperature of one unit mass of a substance by one degree Celsius or Kelvin.

Applications of Thermodynamics

• Engines: Devices that convert heat into work, such as steam engines, internal combustion engines, and jet engines.
• Refrigerators: Devices that transfer heat from a cold reservoir to a hot reservoir, using work to accomplish this transfer.
• Chemical Reactions: Thermodynamic principles are crucial for understanding the feasibility and direction of chemical reactions, such as determining if a reaction is spontaneous or requires energy input.
• Phase Transitions: The study of phase transitions (solid, liquid, gas) is a key application of thermodynamics. Thermodynamics helps predict the conditions under which phase transitions occur, like melting or boiling points.
• Power Plants: Thermodynamics is the foundation for designing efficient power plants.

Energy and Work

• Work is a form of energy transfer that occurs when a force acts on an object and causes it to move.
• Thermodynamic work involves a change in volume. This type of work is important for understanding how systems can do work and is connected with pressure-volume relationships.
• Different types of energy are studied in the context of thermodynamics, including but not limited to mechanical energy, thermal energy, and chemical energy.

Real-World Systems

• Thermodynamics is crucial in understanding complex systems, such as weather patterns, planetary atmospheres, and biological processes involving heat and energy flow.
• It underpins many engineering disciplines, including mechanical, chemical, and aerospace engineering.