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Thermodynamics

NCERT Class 11 Physics Chapter 11

Thermodynamics for Class 11 Physics, JEE and NEET: zeroth and first laws, internal energy, work, isothermal and adiabatic processes and the second law.

10 topics Updated 8 Nov 2026

For: Class 11, JEE and NEET, unless a topic says otherwise

In the syllabus: JEE Class 11 syllabus, NEET Class 11 syllabus

With your textbook

NCERT Physics Part II (Class 11), Chapter 11 “Thermodynamics”, reprint 2026-27.

Open the official NCERT chapter (PDF, 1.8 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Thermal equilibrium

    Definition, equilibrium states, adiabatic and diathermic walls, everyday examples and solved problems.

    NCERT Sections 11.1–11.2 12 min read 3 solved examples 6 practice questions

  2. Zeroth law of thermodynamics

    The statement, the experiment behind it, how it defines temperature and justifies thermometers.

    NCERT Section 11.3 9 min read 4 solved examples 6 practice questions

  3. Heat, internal energy and work

    Internal energy, heat and work for Class 11 Physics, JEE and NEET: internal energy as a state variable, heat as energy in transit, and solved examples.

    NCERT Section 11.4 12 min read 4 solved examples 6 practice questions

  4. First law of thermodynamics

    First law of thermodynamics for Class 11 Physics, JEE and NEET: ΔQ = ΔU + ΔW, sign conventions, work PΔV at constant pressure, and solved examples.

    NCERT Section 11.5 13 min read 5 solved examples 6 practice questions

  5. Specific heat capacity of solids, water and gases

    Relation between Cp and Cv for Class 11 Physics, JEE and NEET: Mayer’s relation Cp − Cv = R with its derivation, 3R for solids and solved examples.

    NCERT Section 11.6 14 min read 5 solved examples 6 practice questions

  6. State variables and equation of state

    State variables for Class 11 Physics, JEE and NEET: equilibrium states, the equation of state PV = μRT, isotherms, extensive and intensive variables.

    NCERT Section 11.7 11 min read 4 solved examples 6 practice questions

  7. Thermodynamic processes

    Thermodynamic processes for Class 11 Physics, JEE and NEET: isothermal, adiabatic, isochoric, isobaric and cyclic, with work and heat in each.

    NCERT Section 11.8 16 min read 6 solved examples 6 practice questions

  8. Second law of thermodynamics

    Kelvin–Planck and Clausius statements, heat engines, refrigerators and why efficiency is below 1.

    NCERT Section 11.9 12 min read 4 solved examples 6 practice questions

  9. Reversible and irreversible processes

    Conditions for reversibility, why real processes are irreversible, with examples.

    NCERT Section 11.10 11 min read 4 solved examples 6 practice questions

  10. Carnot engine

    The four steps of the Carnot cycle, efficiency η = 1 − T/T with its derivation, Carnot’s theorem and solved examples.

    Class 11 only NCERT Section 11.11 14 min read 5 solved examples 6 practice questions

Key formulas in this chapter

Thermal equilibrium

  • Thermal equilibrium: TA = TB
  • Rigid container (ideal gas): P ∝ T

Zeroth law of thermodynamics

  • TA = TC and TB = TC ⇒ TA = TB
  • T = 273.16 K × (P/Ptr), Ptr = pressure at the triple point of water

Heat, internal energy and work

  • U = microscopic kinetic + potential energy (excluding organised bulk and external potential energy)
  • ΔU depends only on the initial and final states

First law of thermodynamics

  • ΔQ = ΔU + ΔW
  • ΔW = PΔV (constant pressure)
  • ΔQ = ΔU + PΔV

Specific heat capacity of solids, water and gases

  • S = ΔQ/ΔT; s = S/m; C = S/μ
  • Cv ≈ 3R ≈ 24.9 J mol K (classical solid, per mole of atoms)
  • 1 historical 15 °C cal ≈ 4.186 J; 1 thermochemical cal = 4.184 J
  • Cp − Cv = R (ideal gas, per mole)

State variables and equation of state

  • PV = μRT (equation of state of an ideal gas)
  • Isotherm: PV = constant (fixed T and μ)

Thermodynamic processes

  • W = μRT ln(V/V) (isothermal)
  • PVγ = constant, γ = Cp/Cv (reversible adiabatic ideal gas, constant γ)
  • W = μR(T − T)/(γ − 1) (adiabatic)
  • W = P(V − V) = μR(T − T) (isobaric)
  • W = 0, ΔQ = ΔU (isochoric)
  • TVγ−1 = constant (reversible adiabatic ideal gas, constant γ)

Second law of thermodynamics

  • Q = W + Q (one cycle)
  • η = W/Q = 1 − Q/Q < 1
  • α = Q/W (refrigerator, finite)

Reversible and irreversible processes

  • Reversible ⇔ quasi-static and no dissipation
  • Insulated free expansion (ideal gas): W = 0, Q = 0, ΔU = 0, yet irreversible

Carnot engine

  • η = 1 − T/T (Carnot engine)
  • Q/T = Q/T
  • W = Q − Q
  • Q = μRT ln(V/V) (isothermal step at T)

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