Short Answer
A thermodynamic process is a change that occurs in a thermodynamic system when one or more of its properties such as pressure, temperature, or volume change. During this process, the system may exchange heat or work with its surroundings.
Examples include heating a gas, compressing air in a pump, or allowing steam to expand in a turbine. Each process follows specific conditions, such as constant temperature or constant pressure, which help in understanding energy transfer in the system.
Detailed Explanation :
Thermodynamic Process
A thermodynamic process refers to any change that takes place within a thermodynamic system. This change may be in pressure, temperature, volume, or internal energy of the system. Thermodynamic processes show how the system moves from one state to another. Each state is defined by specific values of properties like pressure (P), volume (V), and temperature (T).
A thermodynamic process is important because it explains how a system exchanges energy with its surroundings in the form of heat or work. These processes form the foundation of thermodynamics, helping us understand the operation of engines, refrigerators, turbines, and many natural phenomena.
State and Change of State
To understand a thermodynamic process, we must first understand what is meant by a state.
A state is the condition of a system at a particular moment, specified by values of state variables such as P, V, T, and internal energy.
A thermodynamic process describes how the system moves from:
- Initial state → Final state
When any of the state variables change, a thermodynamic process occurs.
Important Features of Thermodynamic Processes
The main characteristics include:
- Change in State Variables
A process involves changes in pressure, volume, temperature, or all of them.
- Exchange of Heat
The system may absorb or release heat.
- Work Done
The system may do work on the surroundings or may have work done on it.
- Path Followed
A process takes place along a particular path on a P–V diagram.
- Initial and Final States
A process always has starting and ending states.
Types of Thermodynamic Processes
Thermodynamic processes are classified based on what remains constant during the process.
- Isothermal Process
- Temperature remains constant
- Heat is exchanged with surroundings
- Example: slow expansion of a gas in contact with a heat reservoir
Mathematical condition:
T = constant
- Adiabatic Process
- No heat exchange
- Temperature changes because gas expands or compresses
- Walls are perfectly insulated
Mathematical condition:
Q = 0
- Isochoric Process (Isovolumetric Process)
- Volume remains constant
- No work is done because the piston cannot move
- Pressure changes with temperature
Mathematical condition:
V = constant
- Isobaric Process
- Pressure remains constant
- System expands or contracts freely
- Heat change results in volume change
Mathematical condition:
P = constant
- Cyclic Process
- System returns to its initial state after completing the process
- Examples include heat engines and refrigerators
In a complete cycle:
Change in internal energy = 0
- Quasi-static Process
- Occurs very slowly
- System remains almost in equilibrium throughout
- Used for theoretical calculations because they are ideal processes
Representation of Thermodynamic Processes
Thermodynamic processes are often shown using a P–V diagram (Pressure vs Volume graph). Each type of process has a characteristic curve:
- Isothermal → smooth hyperbolic curve
- Isochoric → vertical line
- Isobaric → horizontal line
- Adiabatic → steeper curve than isothermal
These graphs help in calculating work done and understanding energy transfer.
Work and Heat in a Thermodynamic Process
During a thermodynamic process:
- Heat (Q) may enter or leave the system
- Work (W) may be done by the system or on the system
The first law of thermodynamics describes this as:
ΔU = Q – W
Where,
ΔU = change in internal energy
The nature of the process decides how Q and W interact.
Importance of Thermodynamic Processes
Thermodynamic processes are important because they explain:
- How heat engines work
- How refrigerators and air conditioners cool
- How steam turbines generate electricity
- How gases expand and compress in nature
- How energy changes in chemical reactions
Without understanding these processes, energy systems could not be designed or analyzed.
Examples of Thermodynamic Processes in Daily Life
- Boiling water (isobaric process)
- Filling air in a cycle pump (adiabatic compression)
- Heating a sealed container (isochoric process)
- Slow expansion of gas in a cylinder (isothermal process)
- Refrigeration cycle (cyclic process)
These examples show that thermodynamic processes occur around us all the time.
Conclusion
A thermodynamic process is a change in the state of a thermodynamic system involving pressure, volume, temperature, or internal energy. It describes how a system moves from one state to another by exchanging heat or work with its surroundings. Thermodynamic processes—such as isothermal, adiabatic, isochoric, and isobaric—play a key role in understanding engines, refrigerators, turbines, and natural phenomena. They form the backbone of thermodynamics and energy science.