JEE Main Chemistry · Equilibrium PYQ

JEE Main Chemical & Ionic Equilibrium PYQ (2002–2025)

Q: How many Equilibrium PYQs should I solve?

Target 70–90 PYQs across 2010–2025. Given 5% weightage and high question density, focused practice yields reliable mock score gains.

Q: Is Chemical Equilibrium or Ionic Equilibrium more tested?

Roughly equal. 50% of PYQs are Chemical Equilibrium (Kp/Kc, Le Chatelier) and 50% are Ionic Equilibrium (pH, buffer, Ksp). Master both.

Q: Do I need logarithm tables for pH calculations?

Not for JEE Main. Questions give enough information to avoid log calculations (e.g., 'given log 2 = 0.301'). But know standard log values: log 2 ≈ 0.301, log 3 ≈ 0.477, log 5 ≈ 0.699.

Q: What's the most-tested Le Chatelier PYQ pattern?

Direction of shift when pressure, temperature or concentration is changed. Key: shift opposes the change. NTA loves asking about pressure effect on reactions where Δn = 0 (no shift).

Q: How do I approach salt hydrolysis questions?

Identify the salt type: strong-strong (pH 7), strong-weak (acidic or basic), weak-weak (Ka vs Kb comparison). Then apply hydrolysis constant formula.

Q: Does Equilibrium connect to Thermodynamics?

Yes — ΔG° = -RT ln K links equilibrium constant to standard Gibbs free energy. Cross-chapter questions (~5% of Equilibrium PYQs) use this bridge.

Equilibrium is a P1 Physical Chemistry chapter combining chemical equilibrium (Kp, Kc, Le Chatelier) and ionic equilibrium (pH, buffer, Ksp) — ~5% JEE Main weightage with 1–2 questions per session. Numerical-heavy and ICE-table-driven; strong pattern repetition.

Equilibrium PYQs from 2002 to 2025, tagged by sub-topic (chemical equilibrium, acid-base, buffer, solubility). Every solution sets up the ICE table and shows equilibrium constant derivation from concentrations.

Practise Chemical & Ionic Equilibrium PYQs All Chemistry PYQs

Chemical & Ionic Equilibrium at a Glance

Weightage

~5%

approx · 10-yr avg

Priority

Must master

Year range

2002–2025

PYQ coverage

Typical in paper

1–2

per session

Key Sub-Topics & What's Tested

Chemical Equilibrium — Kp, Kc

Relationship Kp = Kc(RT)^Δn, homogeneous vs heterogeneous equilibrium, reaction quotient Q vs K.

Le Chatelier's Principle

Effect of concentration, pressure, volume, temperature on equilibrium position; catalyst has no effect on equilibrium position.

Degree of Dissociation

α = dissociated amount / initial amount, relationship with Kc, dependence on concentration and temperature.

Acids & Bases

Arrhenius, Brønsted-Lowry, Lewis definitions, conjugate acid-base pairs, strong vs weak acids/bases, ionisation constants Ka, Kb.

pH Calculations

pH = -log[H⁺], pOH = -log[OH⁻], pH + pOH = 14, calculations for strong acids/bases and weak electrolytes.

Buffer Solutions

Henderson-Hasselbalch equation pH = pKa + log([A⁻]/[HA]), buffer capacity, buffer action explained, common buffer systems.

Solubility Product (Ksp)

Ksp for sparingly soluble salts, common ion effect (decreases solubility), solubility calculation from Ksp.

Salt Hydrolysis

Salts of strong acid + strong base (neutral), strong acid + weak base (acidic), weak acid + strong base (basic), weak acid + weak base (depends on Ka vs Kb).

Question Type Distribution

Question Type	Share (approx)	Example Pattern
Equilibrium Constant Calculation	20%	For 2SO₂ + O₂ ⇌ 2SO₃, given initial and equilibrium concentrations, find Kc.
Le Chatelier Direction Prediction	15%	Predict direction of equilibrium shift when pressure is doubled for 2NO₂ ⇌ N₂O₄.
pH Calculation	25%	Calculate pH of 0.01 M HCl, 0.01 M NaOH, or 0.01 M weak acid with Ka = 1.8×10⁻⁵.
Buffer Solution Problems	15%	Find pH of buffer containing 0.1 M acetic acid and 0.1 M sodium acetate.
Solubility / Common Ion	15%	Ksp of AgCl is 1.6×10⁻¹⁰. Find solubility in pure water and in 0.1 M NaCl.
Salt Hydrolysis	10%	Calculate pH of 0.1 M NH₄Cl solution given Kb of NH₃.

How to Solve Chemical & Ionic Equilibrium PYQs

1
Always set up ICE table. Initial, Change, Equilibrium — rows for each species. Eliminates algebra errors in equilibrium concentration calculations.
2
Kp vs Kc: use Δn carefully. Kp = Kc(RT)^Δn where Δn = moles of gas products - moles of gas reactants. Sign of Δn matters — double-check.
3
Henderson-Hasselbalch for buffer pH. pH = pKa + log([conjugate base]/[acid]). Direct application — no deep derivation needed.
4
Common ion effect: Ksp stays, solubility drops. Adding a common ion to saturated solution pushes dissolution equilibrium left, reducing solubility. Calculate using modified ICE.
5
For weak acid dissociation, approximate if α is small. If Ka << C (concentration), α ≈ √(Ka/C). Saves algebra when exact solution isn't needed.
6
pH of water is 7 at 25°C; pH + pOH = 14 (also at 25°C). Both change at other temperatures. JEE Main assumes 25°C unless stated.

Common Mistakes That Cost Marks

Ignoring units in Kp calculations. Kp can have units depending on Δn. Kp units = (atm)^Δn or (bar)^Δn. Missing units = wrong numeric answer.
Treating water autoionisation (10⁻⁷) for strong solutions. For 0.1 M HCl, autoionisation is negligible. For 10⁻⁷ M HCl, you must account for water — pH is NOT 7 trivially.
Wrong formula for weak acid. pH = -log[H⁺] where [H⁺] = √(Ka·C), not Ka·C directly. Square root factor is easy to miss.
Common ion effect direction backwards. Common ion DECREASES solubility (pushes equilibrium backward). Don't reverse this.
Assuming buffer maintains pH indefinitely. Buffer capacity is finite. Once one component is depleted, buffer breaks.

JEE Main Chemistry PYQ Chapter-Wise

Browse PYQs across all Chemistry chapters.

JEE Main Chemical Thermodynamics PYQ

Connects via ΔG° = -RT ln K — Physical Chemistry partner.

JEE Main Electrochemistry PYQ

Nernst equation extends equilibrium to redox cells.

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JEE Main Chemistry Syllabus with Priority Tiers

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JEE Main Chemistry Mock Test

Full subject + Physical-block mocks.

Frequently asked questions

How many Equilibrium PYQs should I solve?