Key Concepts in Thermodynamics

Definitions
- Thermodynamics: The study of energy, heat, and work and how they relate to physical systems.
- System: The part of the universe being studied (e.g., gas in a cylinder).
- Surroundings: Everything outside the system.
- Boundary: The separation between system and surroundings.
Types of Systems
- Isolated: No exchange of heat or matter with surroundings.
- Closed: Exchanges energy but not matter.
- Open: Exchanges both energy and matter.
Laws of Thermodynamics
- Zeroth Law: If two systems are in thermal equilibrium with a third, they are in equilibrium with each other.
- First Law: Energy cannot be created or destroyed (ΔU = Q - W).
  - ΔU: Change in internal energy
  - Q: Heat added to the system
  - W: Work done by the system
- Second Law: Heat cannot spontaneously flow from a colder body to a hotter body (involves entropy).
  - Entropy (S): Measure of disorder or randomness in a system; tends to increase in isolated systems.
- Third Law: As temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.
Processes
- Isothermal: Constant temperature (ΔU = 0).
- Adiabatic: No heat transfer (Q = 0).
- Isobaric: Constant pressure.
- Isochoric: Constant volume.
Key Terms
- Work (W): Energy transferred when a force moves an object.
- Heat (Q): Energy transferred due to temperature difference.
- Internal Energy (U): Total energy contained within the system.
- Enthalpy (H): Total heat content of a system (H = U + PV).
Thermodynamic Cycles
- Carnot Cycle: Idealized cycle that provides maximum efficient conversion of heat into work. Consists of isothermal and adiabatic processes.
- Otto Cycle: Engine cycle used in gasoline engines.
- Diesel Cycle: Cycle used in diesel engines.
Perpetual Motion Machines
- Devices that violate the first or second law of thermodynamics are impossible to construct.
Applications
- Heat Engines: Convert heat energy into mechanical work.
- Refrigerators: Transfer heat from a cooler area to a warmer area, using work input.
Thermodynamic Equations
- The ideal gas law: PV = nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature.
Units
- Energy: Joules (J)
- Heat: Joules (J) or calories (cal)
- Work: Joules (J)
- Temperature: Kelvin (K), Celsius (°C), Fahrenheit (°F)

These notes summarize core concepts, laws, and applications in thermodynamics, providing a foundational understanding.

Thermodynamics: Key Concepts

Thermodynamics is the study of energy, heat, and how they relate to physical systems
A system is the portion of the universe being studied (e.g., gas in a container)
Surroundings refer to everything outside of the system.
The boundary separates the system from the surroundings.

Types of Thermodynamic Systems

Isolated System: No exchange of heat or matter with the surroundings.
Closed System: Exchanges energy but not matter with the surroundings.
Open System: Exchanges both energy and matter with the surroundings.

Laws of Thermodynamics

Zeroth Law: If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
First Law: Energy cannot be created or destroyed, only transferred or transformed.
- ΔU = Q - W where:
  - ΔU is the change in internal energy
  - Q is the heat added to the system
  - W is the work done by the system
Second Law: Heat cannot spontaneously flow from a colder body to a hotter body (involves entropy).
- Entropy: A measure of disorder or randomness in a system, tends to increase in isolated systems.
Third Law: As the temperature of a system approaches absolute zero (0 Kelvin), the entropy of a perfect crystal approaches zero.

Thermodynamic Processes

Isothermal Process: Occurs at constant temperature (ΔU = 0)
Adiabatic Process: No heat transfer (Q = 0)
Isobaric Process: Occurs at constant pressure.
Isochoric Process: Occurs at constant volume.

Important Terms

Work (W): Energy transferred when a force moves an object.
Heat (Q): Energy transferred due to a temperature difference.
Internal Energy (U): Total energy contained within the system.
Enthalpy (H): Total heat content of a system (H = U + PV).

Thermodynamic Cycles

Carnot Cycle: Idealized cycle that provides the maximum efficiency in converting heat into work, consisting of isothermal and adiabatic processes.
Otto Cycle: Engine cycle used in gasoline engines.
Diesel Cycle: Cycle used in diesel engines.