THERMODYNAMICS
🔷 Topic 1: Basic Concepts of Thermodynamics
1. What is Thermodynamics?
Thermodynamics is the study of energy transformations involving heat and work, and how they affect the physical properties of
systems. It provides a framework to understand how energy flows and changes within matter.
2. Key Terms
System: The specific part of the universe you’re focusing on (e.g., gas in a cylinder).
Surroundings: Everything outside the system that can interact with it.
Boundary: The surface (real or imaginary) that separates the system from the surroundings. It can be:
o Fixed or movable
o Rigid or flexible
o Insulated or conducting
3. Types of Thermodynamic Systems
Type Matter Exchange Energy Exchange Example
Open System Yes Yes Boiling water in an open pot
Closed System No Yes Gas in a sealed, movable piston
Isolated System No No Thermos flask (idealized)
4. Thermodynamic State and State Variables
A thermodynamic state is defined by measurable properties (also called state variables or state functions) such as:
o Pressure (P)
o Volume (V)
o Temperature (T)
o Internal Energy (U)
If these values are known, the system’s state is fully described.
State functions depend only on the current state—not on the path taken to reach it.
5. Thermodynamic Processes
A process is a change that moves a system from one state to another.
The path refers to the sequence of intermediate states the system passes through.
A cycle is a sequence of processes that returns the system to its original state.
o Example: In engines, the working substance undergoes a cyclic process.
o
,6. Quasi-static and Reversible Processes
Quasi-static Process:
o Occurs infinitely slowly so that the system remains nearly in equilibrium at every stage.
o Often used in theoretical analysis for simplicity.
Reversible Process:
o A perfect, idealized process that can be reversed with no energy loss.
o No friction, turbulence, or dissipative effects.
o All reversible processes are quasi-static, but not all quasi-static processes are reversible.
🔷 Topic 2: Zeroth Law of Thermodynamics
1. Statement of the Zeroth Law
The Zeroth Law of Thermodynamics states:
"If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other."
This law defines the concept of temperature in a meaningful way.
2. Explanation
Suppose you have three systems: A, B, and C.
If system A is in thermal equilibrium with system C, and system B is also in thermal equilibrium with system C, then A and B
must be in thermal equilibrium with each other.
Thermal equilibrium means no net heat flows between the systems—they are at the same temperature.
3. Importance
The Zeroth Law allows us to use thermometers to measure temperature.
It provides the foundation for temperature scales (Celsius, Fahrenheit, Kelvin, etc.).
It establishes temperature as a fundamental and measurable property of matter.
4. Example
Imagine:
System A: a cup of water
System B: a metal rod
System C: a thermometer
If the thermometer reads the same temperature when placed in both A and B separately, then A and B are at the same
temperature—they are in thermal equilibrium, even if they never touch.
,🔷 Topic 3: First Law of Thermodynamics
1. Statement of the First Law
"Energy cannot be created or destroyed, only transformed from one form to another."
In thermodynamics, it’s often written as:
ΔU=Q−W\Delta U = Q - WΔU=Q−W
Where:
ΔU\Delta UΔU = Change in internal energy of the system
QQQ = Heat added to the system
WWW = Work done by the system on its surroundings
2. Key Concepts
Internal Energy (U): The total energy contained within a system due to molecular motion and interactions.
Heat (Q): Energy transferred due to temperature difference.
Work (W): Energy transferred when a force is applied over a distance (e.g., gas expanding against a piston).
Sign convention:
Q>0Q > 0Q>0: Heat is added to the system
W>0W > 0W>0: System does work on the surroundings
ΔU>0\Delta U > 0ΔU>0: Internal energy increases
3. Special Processes and First Law Forms
Process Type Description First Law Form
Isothermal Constant temperature (ΔU = 0) Q=WQ = WQ=W
Adiabatic No heat exchange (Q = 0) ΔU=−W\Delta U = -WΔU=−W
Isobaric Constant pressure Q=ΔU+PΔVQ = \Delta U + P\Delta VQ=ΔU+PΔV
Isochoric Constant volume (W = 0) Q=ΔUQ = \Delta UQ=ΔU
4. Applications
Understanding energy flow in:
o Engines
o Refrigerators
o Compressors
Basis for designing thermodynamic cycles (e.g., Carnot, Otto)
5. Example
When a gas is heated:
🔷 Topic 1: Basic Concepts of Thermodynamics
1. What is Thermodynamics?
Thermodynamics is the study of energy transformations involving heat and work, and how they affect the physical properties of
systems. It provides a framework to understand how energy flows and changes within matter.
2. Key Terms
System: The specific part of the universe you’re focusing on (e.g., gas in a cylinder).
Surroundings: Everything outside the system that can interact with it.
Boundary: The surface (real or imaginary) that separates the system from the surroundings. It can be:
o Fixed or movable
o Rigid or flexible
o Insulated or conducting
3. Types of Thermodynamic Systems
Type Matter Exchange Energy Exchange Example
Open System Yes Yes Boiling water in an open pot
Closed System No Yes Gas in a sealed, movable piston
Isolated System No No Thermos flask (idealized)
4. Thermodynamic State and State Variables
A thermodynamic state is defined by measurable properties (also called state variables or state functions) such as:
o Pressure (P)
o Volume (V)
o Temperature (T)
o Internal Energy (U)
If these values are known, the system’s state is fully described.
State functions depend only on the current state—not on the path taken to reach it.
5. Thermodynamic Processes
A process is a change that moves a system from one state to another.
The path refers to the sequence of intermediate states the system passes through.
A cycle is a sequence of processes that returns the system to its original state.
o Example: In engines, the working substance undergoes a cyclic process.
o
,6. Quasi-static and Reversible Processes
Quasi-static Process:
o Occurs infinitely slowly so that the system remains nearly in equilibrium at every stage.
o Often used in theoretical analysis for simplicity.
Reversible Process:
o A perfect, idealized process that can be reversed with no energy loss.
o No friction, turbulence, or dissipative effects.
o All reversible processes are quasi-static, but not all quasi-static processes are reversible.
🔷 Topic 2: Zeroth Law of Thermodynamics
1. Statement of the Zeroth Law
The Zeroth Law of Thermodynamics states:
"If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other."
This law defines the concept of temperature in a meaningful way.
2. Explanation
Suppose you have three systems: A, B, and C.
If system A is in thermal equilibrium with system C, and system B is also in thermal equilibrium with system C, then A and B
must be in thermal equilibrium with each other.
Thermal equilibrium means no net heat flows between the systems—they are at the same temperature.
3. Importance
The Zeroth Law allows us to use thermometers to measure temperature.
It provides the foundation for temperature scales (Celsius, Fahrenheit, Kelvin, etc.).
It establishes temperature as a fundamental and measurable property of matter.
4. Example
Imagine:
System A: a cup of water
System B: a metal rod
System C: a thermometer
If the thermometer reads the same temperature when placed in both A and B separately, then A and B are at the same
temperature—they are in thermal equilibrium, even if they never touch.
,🔷 Topic 3: First Law of Thermodynamics
1. Statement of the First Law
"Energy cannot be created or destroyed, only transformed from one form to another."
In thermodynamics, it’s often written as:
ΔU=Q−W\Delta U = Q - WΔU=Q−W
Where:
ΔU\Delta UΔU = Change in internal energy of the system
QQQ = Heat added to the system
WWW = Work done by the system on its surroundings
2. Key Concepts
Internal Energy (U): The total energy contained within a system due to molecular motion and interactions.
Heat (Q): Energy transferred due to temperature difference.
Work (W): Energy transferred when a force is applied over a distance (e.g., gas expanding against a piston).
Sign convention:
Q>0Q > 0Q>0: Heat is added to the system
W>0W > 0W>0: System does work on the surroundings
ΔU>0\Delta U > 0ΔU>0: Internal energy increases
3. Special Processes and First Law Forms
Process Type Description First Law Form
Isothermal Constant temperature (ΔU = 0) Q=WQ = WQ=W
Adiabatic No heat exchange (Q = 0) ΔU=−W\Delta U = -WΔU=−W
Isobaric Constant pressure Q=ΔU+PΔVQ = \Delta U + P\Delta VQ=ΔU+PΔV
Isochoric Constant volume (W = 0) Q=ΔUQ = \Delta UQ=ΔU
4. Applications
Understanding energy flow in:
o Engines
o Refrigerators
o Compressors
Basis for designing thermodynamic cycles (e.g., Carnot, Otto)
5. Example
When a gas is heated:
