When is a chemical reaction spontaneous?

When ΔG = ΔH − TΔS is negative. ΔH negative and ΔS positive means spontaneous at all temperatures. Both same sign means temperature decides: exothermic-ordering only at low T, endothermic-disordering only at high T. Threshold is T = ΔH/ΔS.

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Thermodynamics & Equilibrium NEET PYQ — The Highest-Weightage Physical Chemistry Block

Q: How many questions come from Thermodynamics and Equilibrium in NEET?

Together these two chapters deliver 5-7 questions per paper, 20 to 28 marks, roughly 10-14% of Chemistry. They are the highest-weightage physical chemistry block. The split is about 40% Thermodynamics, 60% Equilibrium.

Q: What is the most tested concept in NEET Thermodynamics?

Gibbs free energy and spontaneity, tied to the ΔG° = −RT ln K bridge linking thermodynamics to equilibrium. The spontaneity matrix of ΔH/ΔS combinations is tested almost every year, usually in assertion-reason format.

Q: Why do students lose marks on the work sign convention?

Chemistry follows IUPAC: ΔU = q + w, where work done ON the system is positive. Physics uses the opposite sign. NTA places the Physics-convention answer in the options to trap students who don't compartmentalise the subject.

Q: Are there actual Thermodynamics and Equilibrium PYQ questions to practice?

This article contains 12 representative PYQs with traps explained. For 200 plus Thermodynamics and Equilibrium PYQs with chapter mapping, TarQ teaching, and Mistake Book tracking, download Logic Bloom free.

Thermodynamics + Equilibrium NEET PYQ (2015-2025). 5-7 questions per paper, the highest-weightage physical chem block. Spontaneity matrix + 12 must-attempt PYQs.

AAAditya Amar, Founder, Logic Bloom9 June 202618 min read

Quick note — which Thermodynamics is this? This is Chemical Thermodynamics (Class 11 Chemistry, Chapter 6) + Equilibrium (Chapter 7): enthalpy, entropy, Gibbs free energy, Kc/Kp, Le Chatelier, and ionic equilibrium (pH, buffers, Ksp). This is NOT Physics thermodynamics (heat engines, Carnot cycle). The two chapters are bridged by ΔG° = −RT ln K, so we analyse them together.

5-7 Questions Per Paper. If You Skip This Block, Your Chemistry Score Is Mathematically Capped.

Here's a number that should reframe how you prioritise revision:

Thermodynamics + Equilibrium delivers 5-7 questions per NEET paper — 20 to 28 marks, the single highest-weightage physical chemistry block in the entire syllabus. A student who glosses over it caps their Chemistry score at roughly 152-156 out of 180, which in competitive states practically eliminates them from top government medical seats. This isn't a block you can afford to be weak in.

It's also the hardest physical chemistry block — the one students fear most. It demands both heavy calculation (logarithms, Ksp cube roots, pH) AND abstract conceptual reasoning (entropy, spontaneity, dynamic equilibrium). But the difficulty is patterned. The same constructs recycle: the spontaneity matrix, the ΔG = −RT ln K bridge, Le Chatelier pressure shifts, and the Kp-Kc conversion. Master the patterns and the fear disappears.

We tracked the full testing pattern across both chapters from every NEET sitting 2015 to 2025. This is our fourth Chemistry PYQ analysis, after Chemical Bonding, Organic Chemistry, and Chemistry Biomolecules.

🎯 We analyzed every Thermodynamics & Equilibrium question NTA has asked. The app has them all — ready to play and practice.
Entropy, spontaneity, and equilibrium shifts feel abstract on paper — but they click when you watch them. Logic Bloom's Playground turns this block into interactive games: shift a reaction with Le Chatelier and watch the equilibrium re-balance, change temperature and see ΔG flip sign, titrate an acid and watch the pH curve move. Then practice every PYQ from this analysis — line by line from NCERT + 10 years of PYQs, mapped to chapter topics. When you're stuck, TarQ teaches the concept. Your Mistake Book catches every sign-convention and unit slip.	Get the app → Free to start.

🎯 We analyzed every Thermodynamics & Equilibrium question NTA has asked. The app has them all — ready to play and practice.

Entropy, spontaneity, and equilibrium shifts feel abstract on paper — but they click when you watch them. Logic Bloom's Playground turns this block into interactive games: shift a reaction with Le Chatelier and watch the equilibrium re-balance, change temperature and see ΔG flip sign, titrate an acid and watch the pH curve move. Then practice every PYQ from this analysis — line by line from NCERT + 10 years of PYQs, mapped to chapter topics. When you're stuck, TarQ teaches the concept. Your Mistake Book catches every sign-convention and unit slip.

Get the app →
Free to start.

How Many Questions: 5-7 Per Paper, Skewed Toward Equilibrium

Year	Thermodynamics	Equilibrium	Total
2025	3	4	7
2024 + Re-exam	3	3	6
2023	3	4	7
2022	2	3	5
2021	2	3	5
2020	2	2	4
2019	2	3	5
2018	2	3	5
2017	2	3	5
2016	2	3	5
2015	2	3	5

The split runs roughly 40% Thermodynamics, 60% Equilibrium. Equilibrium dominates because Ionic Equilibrium alone (pH, buffers, salt hydrolysis, solubility product) is a vast testing ground that reliably yields 2-3 questions by itself. Physical equilibrium (Le Chatelier, Kp/Kc) adds another. Together with thermodynamics, this is a 24-mark block on average.

Sub-Topic Frequency: Solubility, Kp/Kc, pH, and Gibbs Lead

Sub-topic	Questions (10 yr)	Status
Solubility Product (Ksp) & Common Ion	9	Dominant
Gibbs Free Energy & Spontaneity	9	Dominant
Equilibrium Constant (Kp/Kc)	8	Dominant
pH & Buffer Calculations	7	Dominant
First Law, Work & ΔU vs ΔH	7	Stable
Le Chatelier's Principle	6	Stable
Hess's Law & Bond Enthalpies	5	Occasional
Salt Hydrolysis	4	Occasional
Thermodynamic Processes (isobaric etc.)	3	Rising
Entropy (standalone)	1	Dormant

Four sub-topics dominate: Ksp, Gibbs/spontaneity, Kp/Kc, and pH/buffers. Together they account for the majority of the block. Notice the balance — two from thermodynamics (Gibbs, First Law) and the rest from equilibrium. If revision time is tight, these four are your highest-yield targets.

The Format Shift: Calculation Down, Concept Up — But Harder

Format	2015–2018	2022–2025
Numerical calculation	75%	45%
Conceptual MCQ	25%	25%
Match / Statement / Assertion-Reason	~0%	30%

Here's the paradox: fewer numericals, but the surviving ones are harder. NTA stopped providing log tables — you're now expected to have memorised log 2, log 3, log 5 and the 2.303 conversion factor cold. Multi-step Hess's Law combustion puzzles are gone (too time-consuming), replaced by the integrated ΔG° = −RT ln K bridge that tests both chapters in one question. The difficulty moved from arithmetic volume to sign conventions, unit conversions, and conceptual depth.

🎯 In Chemistry, work done ON the system is POSITIVE. In Physics, work done BY the system is positive. NTA puts the Physics answer as Option A.
This is the single most exploited trap in the block. Chemistry follows IUPAC: ΔU = q + w, where w is positive for compression (work done on the system). Physics uses the opposite sign. NTA deliberately places the Physics-convention answer in the options to catch students who don't compartmentalise which subject they're in. Understanding why the conventions differ — instead of blindly applying a formula — is the only defence. Logic Bloom's Playground lets you compress and expand a gas and watch the work sign flip with the IUPAC convention — with TarQ explaining the logic. Then practice every PYQ and let your Mistake Book catch the sign errors before the exam does.	Play the process → Free to start.

🎯 In Chemistry, work done ON the system is POSITIVE. In Physics, work done BY the system is positive. NTA puts the Physics answer as Option A.

This is the single most exploited trap in the block. Chemistry follows IUPAC: ΔU = q + w, where w is positive for compression (work done on the system). Physics uses the opposite sign. NTA deliberately places the Physics-convention answer in the options to catch students who don't compartmentalise which subject they're in. Understanding why the conventions differ — instead of blindly applying a formula — is the only defence. Logic Bloom's Playground lets you compress and expand a gas and watch the work sign flip with the IUPAC convention — with TarQ explaining the logic. Then practice every PYQ and let your Mistake Book catch the sign errors before the exam does.

Play the process →
Free to start.

The Spontaneity Matrix — Memorise This Cold

This is the single most-tested thermodynamics concept, and NTA weaponises it in assertion-reason format every year. The sign of ΔG = ΔH − TΔS decides spontaneity, and the ΔH/ΔS combination decides how temperature affects it:

🎯 The Spontaneity Matrix — When Is a Reaction Spontaneous?
ΔH	ΔS	Spontaneous?	Example
Negative (exothermic)	Positive (disordering)	Always spontaneous (all T)	Combustion of fuel
Positive (endothermic)	Negative (ordering)	Never spontaneous (any T)	Ozone formation
Negative (exothermic)	Negative (ordering)	Spontaneous only at LOW T	Freezing of water
Positive (endothermic)	Positive (disordering)	Spontaneous only at HIGH T	Boiling of water

The logic: ΔG must be negative for spontaneity. When ΔH and ΔS have the same sign, temperature decides — high T favours the TΔS term, low T favours the ΔH term. The threshold temperature is T = ΔH/ΔS. NTA loves the endothermic + disordering case (spontaneous only at high T) because it's counter-intuitive.

The ΔG° = −RT ln K Bridge — Why Both Chapters Are One

This single equation is the most-tested conceptual bridge in the block, and it's why thermodynamics and equilibrium belong together:

Relationship	What It Tells You
ΔG° = −RT ln K = −2.303 RT log K	Links the energetics of a reaction to its equilibrium position
K > 1 → ΔG° negative	Products favoured, reaction spontaneous in forward direction
K < 1 → ΔG° positive	Reactants favoured, forward reaction non-spontaneous
K = 1 → ΔG° = 0	System at standard equilibrium
Q vs K (reaction quotient)	Q < K → shifts forward; Q > K → shifts reverse; Q = K → at equilibrium

The 2.303 trap: When converting ln K to log K, you must multiply by 2.303 (ln K = 2.303 log K). NTA puts the answer calculated without the 2.303 factor as a distractor. And it tests both chapters in one question — give you ΔH and ΔS, make you find ΔG, then K. Two chapters, one question, double the discrimination.

The 4 Calculation Traps NTA Exploits Every Year

📌 4 Documented Traps — Know Them, Dodge Them
1. The Unit Mismatch Trap In ΔG = ΔH − TΔS	ΔH is given in kJ/mol, ΔS in J/(K·mol). Students forget to convert — dividing ΔH (kJ) by ΔS (J) gives a temperature off by a factor of 1000. Always convert both to the same unit first. NTA includes the unconverted answer as a distractor.
2. The Solid/Liquid Δng Trap In Kp = Kc(RT)^Δng	Δng counts ONLY gaseous moles. For CaCO₃(s) → CaO(s) + CO₂(g), Δng = 1 − 0 = 1 (solids excluded). Students count solids and get Δng = 0, wrongly concluding Kp = Kc.
3. The Ksp Square/Cube Trap For salts like CaF₂	CaF₂ → Ca²⁺ + 2F⁻. Ksp = [Ca²⁺][F⁻]² = (s)(2s)² = 4s³. Students forget to BOTH double the fluoride (2s) AND square it. The coefficient becomes the exponent and the multiplier.
4. The Wrong R-Value Trap In Kp-Kc conversion	For gas equilibria use R = 0.0821 L·atm/(K·mol), NOT 8.314 J/(K·mol). Students grab the thermodynamics R value and get a wrong Kp. Match the R to the units in the problem.

Le Chatelier: Pressure Shifts Are Tested 3× More Than Temperature

NTA's favourite Le Chatelier perturbation is pressure/volume, and the trap is always the same — miscounting gaseous moles in heterogeneous equilibria:

Perturbation	Effect on Equilibrium
Increase pressure (decrease volume)	Shifts toward the side with FEWER gas moles
Increase temperature	Shifts in the endothermic direction (absorbs the added heat)
Increase concentration of a reactant	Shifts forward (toward products)
Add a catalyst	NO shift — speeds both directions equally, Kc unchanged

The classic application: The Haber process (N₂ + 3H₂ ⇌ 2NH₃, ΔH < 0) needs high pressure (fewer moles on product side: 4 → 2), low temperature (exothermic), and continuous removal of NH₃ for maximum yield. The heterogeneous trap: in C(s) + CO₂(g) ⇌ 2CO(g), only gases count — 1 mole gas left, 2 moles gas right, so increased pressure shifts BACKWARD.

The 15 Formulas You Must Know Cold

🎯 15 Exam-Critical Formulas — Each Has Been Tested
1.	First Law: ΔU = q + w	IUPAC: w positive when work done ON system (compression).
2.	Irreversible work: w = −P_ext(V₂−V₁)	Convert L·atm to Joules (×101.3).
3.	Reversible isothermal work: w = −2.303 nRT log(V₂/V₁)	For ideal gas, ΔU = 0 here (ΔT = 0).
4.	ΔH = ΔU + Δng RT	Δng = gaseous products − gaseous reactants.
5.	Gibbs: ΔG = ΔH − TΔS	Negative ΔG = spontaneous. Watch unit mismatch.
6.	Bridge: ΔG° = −2.303 RT log K	Don't drop the negative sign or the 2.303.
7.	Kp = Kc(RT)^Δng	Use R = 0.0821. Kp = Kc only when Δng = 0.
8.	Reaction quotient Q	Q < K → forward. Q > K → reverse.
9.	Kw = [H⁺][OH⁻] = 10⁻¹⁴	At 298 K. pH + pOH = 14.
10.	pH = −log[H⁺]	Foundational ionic equilibrium formula.
11.	Weak acid: [H⁺] = √(Ka·C)	Ostwald's law, valid when α < 0.05.
12.	Henderson: pH = pKa + log([salt]/[acid])	For acidic buffers.
13.	WA-WB salt: pH = 7 + ½(pKa − pKb)	Hydrolysis of weak acid–weak base salt.
14.	Ksp (AₓBᵧ): Ksp = xˣyʸs^(x+y)	For CaF₂: 4s³. Double AND square the F⁻.
15.	Spontaneity threshold: T = ΔH/ΔS	Above/below this T determines spontaneity.

Cross-Chapter Connections

Cross-Chapter Link	What It Tests	Example
Thermodynamics ↔ Equilibrium	The ΔG° = −RT ln K bridge	Given ΔH and ΔS → find ΔG → find K. Tests both chapters in one question.
Thermodynamics + Electrochemistry	ΔG° = −nFE°cell	Positive E° → negative ΔG → spontaneous cell reaction. Assertion-reason favourite.
Equilibrium + Chemical Kinetics	Kc = kf/kb	A catalyst speeds both kf and kb equally → Kc unchanged. Common conceptual test.
Thermodynamics + Chemical Bonding	Bond enthalpy in Hess's law	ΔH_rxn = ΣBE(reactants) − ΣBE(products).

Re-NEET 2026 / NEET 2027 Predictions

Top 5 Sub-Topics Most Likely to Appear

#	Predicted Topic	Why It's Due
1	ΔG° = −2.303 RT log K bridge numerical	Calculate K from ΔH and ΔS data. NTA's favourite two-chapter discriminator. The 2.303 and sign are the traps.
2	Buffer action (Henderson-Hasselbalch)	Identify a weak acid + its salt, then calculate pH. The "excess weak acid" condition is the trap (full neutralisation ≠ buffer).
3	Common ion effect on Ksp	Solubility of AgCl in 0.1 M NaCl. The common ion dominates → simplifies to Ksp/[Cl⁻]. Students compute √Ksp by reflex.
4	P-V graph → process matching	Match isothermal/adiabatic/isochoric/isobaric to their criteria (ΔT=0, q=0, ΔV=0, ΔP=0). Match-the-column format.
5	Le Chatelier on the Haber process	Conditions for max NH₃ yield: high pressure, low temperature, remove product. Industrial application.

3 Concepts Due for a Return

Concept	Status	Likely Format
Degree of dissociation & vapour density	Dormant since ~2018	D/d = 1 + (n−1)α for PCl₅ dissociation. Numerical.
Entropy of phase transition	Dormant since ~2019	ΔS_vap = ΔH_vap/T_b. Simple but unpracticed.
Ostwald's dilution law	Rarely tested	[H⁺] = √(Ka·C) for a very weak acid. Quick approximation.

Thermodynamics & Equilibrium NEET PYQs (2015–2025) — 12 Questions You Must Attempt

These 12 questions represent the core of NTA's testing across both chapters. Each tests a concept repeated multiple times. For each, we explain the specific NTA trap — the mistake that costs you 5 marks (4 lost + 1 negative).

📌 12 Must-Attempt Thermodynamics & Equilibrium PYQs — With the NTA Trap Explained
1. Isothermal ΔU (2022)	1 mole ideal gas at 300 K expands isothermally 1 L → 10 L. Find ΔU. Answer: 0 J. Trap: The volume data tempts you to calculate work. But isothermal + ideal gas → ΔT = 0 → ΔU = 0. The numbers are bait.
2. ΔH vs ΔU (2023)	For CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), relate ΔH and ΔU. Answer: ΔH = ΔU − 2RT. Trap: Counting liquid water in Δng. Only gases: Δng = 1 − 3 = −2.
3. Spontaneity Threshold (2021)	ΔH = 35.5 kJ/mol, ΔS = 83.6 J/K/mol. Above what T is it spontaneous? Answer: T > 425 K. Trap: Unit mismatch. Convert 35.5 kJ to 35500 J before dividing by 83.6. Forgetting gives 0.425 K.
4. Gibbs-Equilibrium Bridge (2020)	Sucrose hydrolysis, Kc = 2×10¹³ at 300 K. Find ΔG°. Answer: −RT ln(2×10¹³), a large negative value. Trap: Dropping the negative sign, or using log without the 2.303 factor.
5. Manipulating K (2017/2015)	If K is for N₂ + 3H₂ ⇌ 2NH₃, what is K for ½N₂ + 3/2H₂ ⇌ NH₃? Answer: √K (K^½). Trap: Dividing K by 2. Halving the equation means taking the square root, not dividing.
6. When Kp = Kc (2024)	For which reaction is Kp = Kc? Answer: H₂(g) + I₂(g) ⇌ 2HI(g). Trap: Kp = Kc only when Δng = 0. Here 2 = 2. Heterogeneous distractors trick you into miscounting solids.
7. Le Chatelier Pressure (2017)	C(s) + CO₂(g) ⇌ 2CO(g). Increase total pressure — which way does it shift? Answer: Backward (toward reactants). Trap: Counting solid carbon. Only gases: 1 mole left, 2 moles right → high pressure favours fewer moles → backward.
8. True Buffer Identification (2022)	Which combination forms an acidic buffer? Answer: 100 mL 0.1 M CH₃COOH + 50 mL 0.1 M NaOH. Trap: Equimolar weak acid + strong base fully neutralises (no buffer). You need EXCESS weak acid left over — here 10 mmol acid, 5 mmol base → 5 mmol acid remains.
9. pH of SA-SB Mixture (2023)	Equal volumes of 0.1 M NaOH and 0.01 M HCl mixed. Final pH? Answer: 12.65. Trap: Averaging the pH values. Find net [OH⁻] = (M₁V₁−M₂V₂)/(V₁+V₂), remembering volume doubles, then pOH → pH.
10. Common Ion Effect (2016)	Solubility of AgCl (Ksp = 1.6×10⁻¹⁰) in 0.1 M NaCl? Answer: 1.6×10⁻⁹ M. Trap: Computing √Ksp as if in pure water. The 0.1 M Cl⁻ dominates → Ksp = [Ag⁺](0.1) → [Ag⁺] = 1.6×10⁻⁹.
11. Conjugate Bases (2019)	Conjugate bases of H₂O and HF? Answer: OH⁻ and F⁻. Trap: Confusing conjugate base (remove H⁺) with conjugate acid (add H⁺). H₃O⁺ is the distractor.
12. State vs Path Variables (2024 Re-exam)	Which variables describe the equilibrium STATE of a system? Answer: Pressure, Volume, Temperature only. Trap: Including Work or Heat. Those are path functions — they describe the transition, not the state.

🎯 These are 12 of the 200+ Thermodynamics & Equilibrium PYQs in the app. Drill all of them.
Every question above is inside Logic Bloom — along with hundreds more from NCERT + 10 years of PYQs, mapped into chapter topics you can learn and master. Play through the simulations first: shift equilibria with Le Chatelier, watch ΔG flip sign with temperature, titrate acids and track the pH curve. When you get a question wrong, TarQ teaches you the concept — not the answer. Your Mistake Book tracks exactly which traps catch you — sign conventions, unit mismatches, the Δng miscount. Then take it all into Battleground — 1v1 duels under real exam pressure. Get Logic Bloom — Free to start →

🎯 These are 12 of the 200+ Thermodynamics & Equilibrium PYQs in the app. Drill all of them.

Every question above is inside Logic Bloom — along with hundreds more from NCERT + 10 years of PYQs, mapped into chapter topics you can learn and master. Play through the simulations first: shift equilibria with Le Chatelier, watch ΔG flip sign with temperature, titrate acids and track the pH curve. When you get a question wrong, TarQ teaches you the concept — not the answer. Your Mistake Book tracks exactly which traps catch you — sign conventions, unit mismatches, the Δng miscount. Then take it all into Battleground — 1v1 duels under real exam pressure.

Get Logic Bloom — Free to start →

How to Prepare Based on the Data

📌 Data-Driven Preparation Strategy for Thermodynamics & Equilibrium NEET 2027
Memorise the spontaneity matrix cold	The four ΔH/ΔS combinations and when each is spontaneous. NTA tests this in assertion-reason every year. Know that endothermic + disordering is spontaneous only at high T — the counter-intuitive case they love.
Master the ΔG° = −RT ln K bridge	It's the most-tested concept because it spans both chapters. Practice going from ΔH and ΔS → ΔG → K in one chain. Never drop the negative sign or the 2.303 factor.
Drill the 4 calculation traps	Unit mismatch (kJ vs J), the solid/liquid Δng miscount, the Ksp square/cube error, and the wrong R-value. Each has a matching distractor in the options. Knowing the trap before you calculate makes you immune.
Memorise log 2, log 3, log 5 and 2.303	NTA stopped giving log tables. log 2 = 0.301, log 3 = 0.477, log 5 = 0.699. You'll need these for every pH and Gibbs calculation. Non-negotiable.
Know the Chemistry sign convention	ΔU = q + w, w positive for work done ON the system (IUPAC). This is opposite to Physics. NTA puts the Physics answer as a distractor — compartmentalise which subject you're in.
Play the processes, practice every PYQ, track your mistakes	Logic Bloom's Playground turns this block into interactive games — shift equilibria, flip ΔG with temperature, track pH curves — with TarQ guiding the concept. Then practice every PYQ: line by line from NCERT + 10 years of PYQs, mapped to chapter topics. Your Mistake Book catches sign and unit errors. Then take it into Battleground — 1v1 duels under real exam pressure. Free to start.

Done analysing? Now play, understand, and master.

🎯 5-7 questions per paper. The highest-weightage physical chem block. Skip it and your Chemistry score is capped. The patterns are here. The practice is in the app.
🎮 Playground Understand through games — with TarQ	Every concept as an interactive game — shift an equilibrium with Le Chatelier and watch it re-balance, change temperature and see ΔG flip sign, titrate an acid and track the pH curve, compress a gas and watch the work sign. Chapter maps break each topic into concept games → readings → MCQs. Line by line from NCERT + 10 years of PYQs, all inside. When you're stuck, TarQ teaches the concept. Mistake Book catches sign and unit errors before the exam does. Get the app →
⚔️ Battleground Score through practice — 1v1 duels	Take the concepts you understood in Playground and test them under real time pressure. Challenge a friend or get matched live. 10 timed questions per match across Physics, Chemistry, Biology. ELO climbs through 6 tiers: Bronze → Silver → Gold → Platinum → Diamond → Archeon. Get the app →
Understand through games. Score through practice. Get Logic Bloom — Free to start →

FAQs — Thermodynamics & Equilibrium NEET PYQ

Q1: How many questions come from Thermodynamics and Equilibrium in NEET?
Together these two chapters deliver 5-7 questions per paper — 20 to 28 marks, roughly 10-14% of Chemistry. This makes them the highest-weightage physical chemistry block in the NEET syllabus. The split runs about 40% Thermodynamics, 60% Equilibrium, with Ionic Equilibrium (pH, buffers, Ksp) alone yielding 2-3 questions.

Q2: What is the most tested concept in NEET Thermodynamics?
Gibbs free energy and spontaneity (9 appearances in 10 years), closely tied to the ΔG° = −RT ln K bridge that links thermodynamics to equilibrium. The spontaneity matrix — which ΔH/ΔS combinations are spontaneous at which temperatures — is tested almost every year, usually in assertion-reason format.

Q3: When is a reaction spontaneous?
A reaction is spontaneous when ΔG = ΔH − TΔS is negative. If ΔH is negative and ΔS positive, it's spontaneous at all temperatures. If ΔH positive and ΔS negative, never. When both have the same sign, temperature decides: exothermic+ordering is spontaneous only at low T; endothermic+disordering only at high T. The threshold is T = ΔH/ΔS.

Q4: Why do students lose marks on the work sign convention?
Chemistry follows the IUPAC convention ΔU = q + w, where work done ON the system (compression) is positive. Physics uses the opposite sign (work done BY the system is positive). NTA deliberately places the Physics-convention answer in the options to trap students who don't compartmentalise which subject they're testing.

Q5: Are there actual Thermodynamics and Equilibrium PYQ questions to practice?
Yes — this article contains 12 representative PYQs with the NTA trap explained for each. For the full set of 200+ Thermodynamics and Equilibrium PYQs mapped to chapter topics with TarQ teaching and a Mistake Book tracking your errors, download Logic Bloom. Free to start.