Thermodynamic Processes
Isothermal, adiabatic, isobaric and isochoric processes and their work expressions. (Physics › Thermodynamics, NEET UG syllabus.)
What is Thermodynamic Processes?
A process that involves changes in the state of a thermodynamic system from an initial equilibrium state to a final equilibrium state.
Key formula / rule: First Law of Thermodynamics
Key points
- Define and differentiate between isothermal, adiabatic, isobaric, and isochoric processes.
- State the conditions and characteristics of each thermodynamic process.
- Apply the First Law of Thermodynamics to each process.
- Calculate work done, heat exchanged, and change in internal energy for each process.
Common exam trap
Confusing the conditions for each process (e.g., assuming Q=0 for isothermal).
Definitions
- Term
Thermodynamic Process
- Meaning
A process that involves changes in the state of a thermodynamic system from an initial equilibrium state to a final equilibrium state.
- Term
Isothermal Process
- Meaning
A thermodynamic process in which the temperature of the system remains constant.
- Term
Adiabatic Process
- Meaning
A thermodynamic process in which no heat is exchanged between the system and its surroundings.
- Term
Isobaric Process
- Meaning
A thermodynamic process in which the pressure of the system remains constant.
- Term
Isochoric Process
- Meaning
A thermodynamic process in which the volume of the system remains constant.
Learning objectives
Define and differentiate between isothermal, adiabatic, isobaric, and isochoric processes.
State the conditions and characteristics of each thermodynamic process.
Apply the First Law of Thermodynamics to each process.
Calculate work done, heat exchanged, and change in internal energy for each process.
Interpret P-V diagrams for different thermodynamic processes.
Formulae
- Name
First Law of Thermodynamics
- Note
ΔU is change in internal energy, Q is heat added to system, W is work done by system.
- Expression
ΔU = Q - W
- Name
Work done in Isothermal process (ideal gas)
- Note
T is constant temperature, n is moles, R is gas constant.
- Expression
W = nRT ln(Vf/Vi) = nRT ln(Π/Pf)
- Name
Work done in Adiabatic process
- Note
γ = Cp/Cv (ratio of specific heats).
- Expression
W = (PiVi - PfVf) / (γ - 1) = nR(Ti - Tf) / (γ - 1)
- Name
Adiabatic relations
- Note
Relates P, V, T for an adiabatic process.
- Expression
PV^γ = constant; TV^(γ-1) = constant; P^(1-γ)T^γ = constant
- Name
Work done in Isobaric process
- Note
P is constant pressure.
- Expression
W = P(Vf - Vi)
- Name
Work done in Isochoric process
- Note
Volume is constant, so no displacement work is done.
- Expression
W = 0
Prerequisites
Basic understanding of pressure, volume, and temperature.
Knowledge of ideal gas laws (PV=nRT).
Familiarity with the concept of internal energy.
Understanding of the First Law of Thermodynamics.
Common mistakes
Confusing the conditions for each process (e.g., assuming Q=0 for isothermal).
Incorrectly applying the work done formula for a specific process.
Forgetting that ΔU=0 only for ideal gases in isothermal processes.
Mixing up the signs of Q and W in the First Law of Thermodynamics.
Not understanding that adiabatic expansion leads to cooling and compression to heating.
Keywords
Isothermal
Adiabatic
Isobaric
Isochoric
Thermodynamic Process
Work Done
Heat Exchange
Internal Energy
First Law of Thermodynamics
P-V Diagram
Practice preview
Which of the following statements is true for an isothermal process?…
easy
The work done by a gas during an isobaric expansion from volume V1 to V2 is given by:…
easy
For a given change in volume, the work done by an ideal gas is maximum in which of the following processes?…
medium