What does Thermodynamics cover for NEET Chemistry?

7 lessons: Enthalpies Various, Enthalpy Heat Capacity, First Law Thermodynamics, Gibbs Free Energy, Hess's Law, Second Law Thermodynamics and Spontaneity Entropy.

How often has Thermodynamics come up in NEET past papers?

Our set of verified past papers has 13 questions from this unit, from NEET 2020, 2021, 2023, 2024, 2025 and 2026. Each is answered against the official NTA key.

Is the Thermodynamics material free?

Yes. All 7 lessons and 56 practice questions are free, with no login needed.

Thermodynamics

7 lessons

Topic index in NCERT order

7 of 7 lessons by the NCERT chapter they teach from, in book order. The page is the first printed page of your NCERT book the lesson cites; PYQs are the past NEET questions on that topic.

Class 11 Chemistry, Chapter 5

Enthalpies Various

8 MCQs1 PYQs2 revision cardsWorked example

Easy Recall (3)Direct Application (3)Calculation (1)Concept Trap (1)

Enthalpy Heat Capacity

8 MCQs2 PYQs2 revision cardsWorked example

Easy Recall (3)Direct Application (3)Calculation (2)

First Law Thermodynamics

8 MCQs3 PYQs1 revision cardWorked example

Direct Application (5)Easy Recall (2)Concept Trap (1)

Gibbs Free Energy

8 MCQs2 PYQs2 revision cardsWorked example

Direct Application (5)Calculation (2)Easy Recall (1)

Hess's Law

8 MCQs6 revision cardsWorked example

Easy Recall (3)Direct Application (3)Calculation (2)

Second Law Thermodynamics

8 MCQs3 revision cardsWorked example

Easy Recall (2)Direct Application (4)Concept Trap (1)Calculation (1)

Spontaneity Entropy

8 MCQs4 PYQs3 revision cardsWorked example

Direct Application (3)Easy Recall (3)Concept Trap (2)

Past-paper questions from this unit

13 questions from NEET 2020, 2021, 2023, 2024, 2025, 2026. Answers verified against NTA official keys.

By year in our set: 2020 (3) · 2021 (2) · 2023 (2) · 2024 (3) · 2025 (1) · 2026 (2)

Lesson: Spontaneity Entropy

NEET 2026

Two moles of an ideal gas undergo free expansion from 10 L to 100 L at 300 K. The values of ΔS_system and ΔS_surroundings are (R is universal gas constant)

1ΔS_system = 0; ΔS_surroundings = 0

2ΔS_system = 4.606 R; ΔS_surroundings = −4.606 R

3ΔS_system = 0; ΔS_surroundings = 4.606 R

4ΔS_system = 4.606 R; ΔS_surroundings = 0

NTA Answer: Option 4(final)

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Lesson: First Law Thermodynamics

NEET 2026

Consider the reversible processes for 1.0 mol of an ideal gas as shown in the figure. w₁, w₂, w₃ and w₄ represent work done (in calories) in the processes 1, 2, 3 and 4, respectively; ΔU₂ and ΔU₄ are changes in the internal energy for the processes 2 and 4, respectively. [use R = 2 cal K⁻¹ mol⁻¹] The correct option is

1w₁ + w₃ = −2T₁ ln(V₂/V₁) − 2T₂ ln(V₄/V₃)

2w₂ + w₄ = ΔU₂ − ΔU₄

3w₁ + w₂ = 2T₁ ln(V₂/V₁)

4w₁ + w₂ + w₃ + w₄ = 0

NTA Answer: Option 1(final)

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Lesson: Enthalpies Various

NEET 2025

The standard heat of formation, in kcal/mol of Ba2+ is : [Given : standard heat of formation of 2– 4 SO ion (aq) = –216 kcal/mol, standard heat of crystallisation of BaSO4(s) = –4.5 kcal/mol, standard heat of formation of BaSO4(s) = – 349 kcal/mol]

1+ 220.5

2– 128.5

3– 133.0

4+ 133.0

NTA Answer: Option 2(final)

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Lesson: Spontaneity Entropy

NEET 2024Revised key

In which of the following processes entropy increases? A. A liquid evaporates to vapour. B. Temperature of a crystalline solid lowered from 130 K to 0 K. C. 2NaHCO₃(s) → Na₂CO₃(s) + CO₂(g) + H₂O(g) D. Cl₂(g) → 2Cl(g) Choose the correct answer from the options given below:

1A and C

2A, B and D

3A, C and D

4C and D

NTA Answer: Option 3(revised_final)

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NEET 2024Revised key

Match List I with List II. List-I List-II (Process) (Conditions) A. Isothermal process I. No heat exchange B. Isochoric process II. Carried out at constant temperature C. Isobaric process III. Carried out at constant volume D. Adiabatic process IV. Carried out at constant pressure Choose the correct answer from the options given below:

1A-IV, B-III, C-II, D-I

2A-IV, B-II, C-III, D-I

3A-I, B-II, C-III, D-IV

4A-II, B-III, C-IV, D-I

NTA Answer: Option 4(revised_final)

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Lesson: First Law Thermodynamics

NEET 2024Revised key

The work done during reversible isothermal expansion of one mole of hydrogen gas at 25°C from pressure of 20 atmosphere to 10 atmosphere is (Given R = 2.0 cal K⁻¹ mol⁻¹)

10 calorie

2–413.14 calories

3413.14 calories

4100 calories

NTA Answer: Option 2(revised_final)

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Lesson: Enthalpy Heat Capacity

NEET 2023

Which amongst the following options is the correct relation between change in enthalpy and change in internal energy?

1ΔH = ΔU + Δn_gRT

2ΔH – ΔU = –ΔnRT

3ΔH + ΔU = ΔnR

4ΔH = ΔU – Δn_gRT

NTA Answer: Option 1(final)

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Lesson: Gibbs Free Energy

NEET 2023

The equilibrium concentrations of the species in the reaction A + B ⇌ C + D are 2, 3, 10 and 6 mol L⁻¹, respectively at 300 K. ΔG° for the reaction is (R = 2 cal/mol K)

1–137.26 cal

2–1381.80 cal

3–13.73 cal

41372.60 cal

NTA Answer: Option 2(final)

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Lesson: Enthalpy Heat Capacity

NEET 2021

Which one among the following is the correct option for right relationship between C_P and C_V for one mole of ideal gas?

1C_V = RC_P

2C_P + C_V = R

3C_P − C_V = R

4C_P = RC_V

NTA Answer: Option 3(final)

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Lesson: Spontaneity Entropy

NEET 2021

For irreversible expansion of an ideal gas under isothermal condition, the correct option is:

1ΔU ≠ 0, ΔS(total) = 0

2ΔU = 0, ΔS(total) = 0

3ΔU ≠ 0, ΔS(total) ≠ 0

4ΔU = 0, ΔS(total) ≠ 0

NTA Answer: Option 4(final)

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Lesson: First Law Thermodynamics

NEET 2020

The correct option for free expansion of an ideal gas under adiabatic condition is :

1q > 0, ∆T > 0 and w > 0

2q=0, ∆T=0 and w=0

3q=0, ∆T < 0 and w > 0

4q < 0, ∆T=0 and w=0

NTA Answer: Option 2(final)

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Lesson: Gibbs Free Energy

NEET 2020

Hydrolysis of sucrose is given by the following reaction. Sucrose + H2O ⇌ Glucose + Fructose. If the equilibrium constant (Kc) is 2×10¹³ at 300 K, the value of ΔrG⊖ at the same temperature will be :

1−8.314 J mol⁻¹K⁻¹ × 300 K × ln(4×10¹³)

2−8.314 J mol⁻¹K⁻¹ × 300 K × ln(2×10¹³)

38.314 J mol⁻¹K⁻¹ × 300 K × ln(2×10¹³)

48.314 J mol⁻¹K⁻¹ × 300 K × ln(3×10¹³)

NTA Answer: Option 2(final)

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Lesson: Spontaneity Entropy

NEET 2020

For the reaction, 2Cl(g) → Cl2 (g), the correct option is :

1∆rH < 0 and ∆rS < 0

2∆rH > 0 and ∆rS > 0

3∆rH > 0 and ∆rS < 0

4∆rH < 0 and ∆rS > 0

NTA Answer: Option 1(final)

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Exam traps and common mistakes in this unit

Lesson: Hess's Law

Trap

Hess's law: ΔH sign on reversal

Category: Sign Convention

When reversing a reaction, ΔH changes sign. Multiply: same as multiply ΔH.

When it triggers

Hess's law problem with combination of multiple reactions.

How to avoid

If reaction is reversed: ΔH → -ΔH. If multiplied by factor n: ΔH → n×ΔH. Apply systematically when combining.

Lesson: Gibbs Free Energy

Mistake

Wrong sign of ΔG° from K. ΔG° = -RT ln K (negative ln means K<1, ΔG°>0).

Root cause: sign error

Correction

K > 1: ln K > 0 → ΔG° < 0 (forward favoured). K < 1: ln K < 0 → ΔG° > 0 (reverse favoured). At equilibrium K=1, ΔG°=0.

Lesson: Gibbs Free Energy

Mistake

Predicts spontaneity from ΔH alone (ignoring T and ΔS).

Root cause: concept gap

Correction

Spontaneity from ΔG = ΔH - TΔS. Endothermic reactions can be spontaneous if TΔS > ΔH (ice melting at room T).

Lesson: Hess's Law

Mistake

Forgets to negate ΔH when reversing a reaction in Hess's law combination.

Root cause: sign error

Correction

Reversing a reaction: ΔH → -ΔH. Multiplying by n: ΔH → n·ΔH. Apply consistently before summing.

Formulas in this unit

Lesson: Enthalpies Various

Standard enthalpy of reaction

Δ H_{rxn}^{\circ} = \sum Δ H_{f}^{\circ} (prod) - \sum Δ H_{f}^{\circ} (react)

From standard formation enthalpies. ΔH°_f of element in standard state = 0.

Symbol	Quantity	SI Unit
ΔH°_f	standard formation enthalpy	kJ/mol

Valid when

Standard state (1 bar, 298 K)
Stoichiometric coefficients applied

Lesson: Enthalpy Heat Capacity

Enthalpy and ΔH at constant P

H = U + P V; Δ H = q_{p}

Enthalpy = internal energy + PV. At constant pressure, heat absorbed equals enthalpy change.

Symbol	Quantity	SI Unit
H	enthalpy	J
U	internal energy	J
P	pressure	Pa
V	volume	m^3

Valid when

At constant pressure
Closed system

Lesson: First Law Thermodynamics

First law of thermodynamics (chemistry)

Δ U = q + w

Internal energy change = heat added to system + work done ON system. Note: chemistry uses w as work done ON system; physics uses w as work done BY.

Symbol	Quantity	SI Unit
ΔU	internal energy change	J
q	heat	J
w	work on system	J

Valid when

Closed system
Sign convention chosen consistently

Lesson: Gibbs Free Energy

Gibbs free energy

Δ G = Δ H - T Δ S

Spontaneity criterion. ΔG<0: spontaneous. ΔG=0: equilibrium. ΔG>0: non-spontaneous.

Symbol	Quantity	SI Unit
ΔG	Gibbs energy change	kJ
ΔH	enthalpy	kJ
ΔS	entropy	kJ/K
T	temperature	K

Valid when

Constant T and P

Lesson: Gibbs Free Energy

ΔG° and K

Δ G^{\circ} = - R T ln K

Standard free energy change relates to equilibrium constant. K>1: ΔG°<0; K<1: ΔG°>0.

Symbol	Quantity	SI Unit
ΔG°	standard free energy	J/mol
R	gas constant 8.314	J/mol/K
T	temp	K
K	equilibrium constant	-

Valid when

Standard state
Equilibrium

Lesson: Hess's Law

Hess's law

Δ H_{net} = \sum Δ H_{steps}

Total enthalpy change is independent of path. Useful for computing ΔH of reactions not directly measurable.

Symbol	Quantity	SI Unit
ΔH	enthalpy change	J or kJ

Valid when

State function (path-independent)
Same initial/final states

NEET question patterns in this unit

Lesson: Gibbs Free Energy

Predict spontaneity from ΔH and ΔS at given T using ΔG = ΔH - TΔS.

InterpretationMedium

Common distractors

ignores temperature

Uses ΔH alone for spontaneity

Lesson: Hess's Law

Combine multiple thermochemical equations using Hess's law to find ΔH of target reaction.

Multi StepMedium

Common distractors

wrong sign when reversing

Forgets to negate ΔH when reversing equation

Questions about this unit

What does Thermodynamics cover for NEET Chemistry?: 7 lessons: Enthalpies Various, Enthalpy Heat Capacity, First Law Thermodynamics, Gibbs Free Energy, Hess's Law, Second Law Thermodynamics and Spontaneity Entropy.
How often has Thermodynamics come up in NEET past papers?: Our set of verified past papers has 13 questions from this unit, from NEET 2020, 2021, 2023, 2024, 2025 and 2026. Each is answered against the official NTA key.
Is the Thermodynamics material free?: Yes. All 7 lessons and 56 practice questions are free, with no login needed.