Isothermal Process Experiment for Schools, Teachers, and Students
An isothermal process is a thermodynamic process in which the temperature of the system remains constant throughout. As a result, the internal energy (ΔU) of the system does not change. Mathematically:
ΔT = 0 and ΔU = 0
Key Features of an Isothermal Process:
- The system’s temperature remains constant during the process (ΔT = 0).
- Since the internal energy depends only on temperature, ΔU = 0.
- Heat added to the system (ΔQ) is completely used to do work (W).
- The pressure and volume of the gas change inversely, maintaining the ideal gas law relationship.
First Law of Thermodynamics for an Isothermal Process:
ΔQ = W
Where:
- ΔQ: Heat supplied to the system,
- W: Work done by or on the system.
Work Done in an Isothermal Process:
For an ideal gas, the work done during an isothermal expansion or compression is:
W = nRT ln(Vf / Vi)
Where:
- n: Number of moles of the gas,
- R: Universal gas constant (8.314 J/mol·K),
- T: Absolute temperature (K),
- Vi, Vf: Initial and final volumes of the gas.
Relation Between Pressure and Volume:
For an isothermal process:
P * V = constant
P1 * V1 = P2 * V2
Where:
- P1, V1: Initial pressure and volume,
- P2, V2: Final pressure and volume.
Examples of Isothermal Processes:
- Boiling of Water: During the boiling process, the temperature of water remains constant while heat is continuously supplied.
- Expansion of Gas in a Cylinder with Heat Exchange: A gas expands isothermally in a cylinder in thermal contact with a reservoir.
- Melting of Ice: The temperature of ice and water remains constant at 0°C during melting.
Applications of Isothermal Processes:
- Industrial Processes: Used in processes involving heat exchange at constant temperature, such as in refrigerators and heat engines.
- Thermodynamic Cycles: Isothermal processes are integral to cycles like the Carnot and Stirling cycles.
- Compressed Air Systems: Air compression at constant temperature prevents overheating.
Graphical Representation:
- Pressure-Volume (P-V) Graph: The graph of an isothermal process is a hyperbolic curve because P * V = constant. Pressure decreases as volume increases and vice versa.
- Temperature-Entropy (T-S) Graph: The graph is a horizontal line, as temperature remains constant.
Observations:
- Temperature remains constant, so ΔU = 0.
- Heat supplied (ΔQ) is entirely used for work (W = ΔQ).
- Pressure and volume are inversely related during an isothermal process.
- Isothermal processes occur slowly to maintain thermal equilibrium.
An isothermal process describes a thermodynamic change at constant temperature. It is essential in understanding heat engines, phase changes, and many natural and industrial phenomena.
