EquilibriumNEET MCQs with solutions
Equilibrium covers chemical and ionic equilibrium — Le Chatelier's principle, equilibrium constants (Kp, Kc), pH, buffer solutions, solubility product and the common ion effect. NEET asks both conceptual and numerical questions, especially on pH calculations, buffer action, and predicting the direction of equilibrium shifts.
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- 11 Chemistry
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Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Important PYQ Mixed Concepts
For the equilibrium 2A(g) ⇌ B(g) + C(g), Kc = 4 × 10⁻³. At a particular instant [A] = [B] = [C] = 2 × 10⁻³ M. What is the tendency of the reaction?
Not quite — the answer is D.
Qc = [B][C]/[A]² = (2 × 10⁻³)²/(2 × 10⁻³)² = 1. Since Qc (1) > Kc (0.004), the system must move backward to reduce Qc. Option A traps students who confuse Qc < Kc with forward direction.
Q2Grand Test
For 2A(g) ⇌ B(g) + C(g), Kc = 4 × 10⁻³. At a particular instant [A] = [B] = [C] = 2 × 10⁻³ M. The reaction will:
Not quite — the answer is D.
Qc = [B][C]/[A]² = (2×10⁻³)(2×10⁻³)/(2×10⁻³)² = 1. Since Qc (1) > Kc (4×10⁻³), the system has excess products and must shift left to reach equilibrium, so the reaction proceeds backward. Option A is wrong because Qc is not less than Kc. Option B is wrong because Qc ≠ Kc. Option C is wrong because the reaction is reversible.
Q3Mixed Revision
For CO₂(g)+C(s)⇌2CO(g), Kp=3.0 at 1000 K. Given R=0.083 L bar K⁻¹mol⁻¹, Kc is:
Not quite — the answer is A.
Δn=2−1=1 (solid C excluded). Kc=Kp/(RT)=3.0/(0.083×1000)=3.0/83≈3.6×10⁻². Options 3.6 and 0.36 arise from incorrect R values or omitting the power of 10.
Q4Equilibrium in Physical Processes
Which condition is essential for establishment of equilibrium between liquid and vapour phase?
Not quite — the answer is A.
A closed system prevents matter from escaping, allowing vapour to accumulate until rates of evaporation and condensation equalise. An open system allows vapour to escape continuously, so equilibrium is never reached. Temperature and pressure alone cannot establish equilibrium without containment.
Q5Dynamic Nature of Equilibrium
At equilibrium, concentration of reactants and products:
Not quite — the answer is B.
Concentrations remain constant at equilibrium because equal rates of forward and reverse reactions balance each other — they need not be equal to each other. Option A is the common misconception that reactants are fully consumed.
Q6Homogeneous and Heterogeneous Equilibria
Which type of equilibrium involves all reacting species in the same phase?
Not quite — the answer is A.
Homogeneous equilibrium is defined by all reactants and products existing in a single phase. Heterogeneous equilibrium (Option B) involves species in two or more different phases. Ionic equilibrium (Option C) is a subcategory, not a phase-based classification.
Q7Solubility Equilibrium Ksp
The solubility product Ksp is correctly defined as:
Not quite — the answer is A.
Ksp = [Aᵐ⁺]ᵐ[Bⁿ⁻]ⁿ at saturation — each ionic concentration raised to its stoichiometric coefficient. Option D is the ionic product Q (before saturation), not Ksp. Option B (sum) has no thermodynamic basis; Ksp is always a product expression.
Q8Law of Chemical Equilibrium (Law of Mass Action)
According to the law of mass action, the rate of a chemical reaction is proportional to:
Not quite — the answer is A.
For aA + bB → products, rate ∝ [A]^a[B]^b — each reactant's concentration is raised to its stoichiometric coefficient. Option D is wrong because rate depends on reactants, not products; Option B (sum) has no physical basis in mass action.
Q9Grand Mixed High Difficulty
For the reaction PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), decreasing the volume of the container at constant temperature will:
Not quite — the answer is A.
Δn = 2 − 1 = +1; moles increase going forward. Decreasing volume increases pressure, which by Le Chatelier shifts equilibrium toward fewer moles of gas — i.e., the reactant side (PCl₅). Option B is the trap: students confuse "pressure increases" with "forward shift" without checking Δn sign.
Q10Ionic Equilibrium Introduction
Which of the following represents ionic equilibrium?
Not quite — the answer is A.
Ionic equilibrium involves reversible dissociation into ions in solution. Option D is a heterogeneous chemical equilibrium, not ionic. Options B and C are gaseous chemical equilibria with no ion formation.
Q11Equilibrium Constant (Kc Kp)
At equilibrium for A(g) + B(g) ⇌ C(g) + D(g), [A]=2M, [B]=2M, [C]=4M, [D]=4M. What is Kc?
Not quite — the answer is D.
Kc = [C][D]/[A][B] = (4×4)/(2×2) = 16/4 = 4. Option A (=1) is the trap when students divide equal-looking numbers incorrectly. Option B arises from adding instead of multiplying concentrations.
Q12Applications of Equilibrium Constant
For a reaction at equilibrium, if Kc >> 1 (e.g., Kc = 10¹⁰), which statement is correct?
Not quite — the answer is A.
Kc >> 1 means the numerator (products) dominates the equilibrium expression — products are heavily favoured. Kc = 10¹⁰ indicates an almost complete forward reaction. Option B applies when Kc << 1; Option C applies when Kc ≈ 1.
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Get RankUp on Google PlayQ13Le Chatelier Principle
According to Le Chatelier's principle, when a system at equilibrium is subjected to a stress, it will:
Not quite — the answer is A.
The system shifts in the direction that opposes the imposed change, minimising its effect — this is Le Chatelier's principle. It does not eliminate the stress entirely, only partially counteracts it. K remains unchanged.
Q14Ionization of Acids and Bases Ka Kb
The acid dissociation constant Ka for a weak acid HA is correctly expressed as:
Not quite — the answer is A.
Ka = [H⁺][A⁻]/[HA] — products in numerator, reactant in denominator, as per equilibrium law. Option B is the inverse expression (equilibrium constant for reverse reaction). Pure solids and liquids (including water) are excluded from Ka expressions.
Q15pH Scale and Calculations
pH of a solution is defined as:
Not quite — the answer is A.
pH = −log[H⁺]; the negative sign converts small H⁺ concentrations into positive, manageable numbers. Option C (−log[OH⁻]) defines pOH — the most common one-letter confusion in NEET. Options B and D omit the negative sign entirely.
Q16Buffer Solutions
A buffer solution resists change in:
Not quite — the answer is A.
Buffers resist significant pH change on addition of small amounts of acid or base. Option C (conductivity) changes on dilution regardless of buffer presence. Option B and D have no connection to buffer function — included to mirror NEET's property-confusion traps.
Q17Common Ion Effect
Which of the following correctly defines the common ion effect?
Not quite — the answer is A.
The common ion effect is the suppression of ionization of a weak electrolyte when an ion common to it is added externally. Option B is opposite — ionization decreases, not increases. Ksp (Option C) remains constant and is unaffected.
Q18Overall Mixed Revision
Which of the following is essential for a system to reach chemical equilibrium?
Not quite — the answer is A.
Equilibrium can only be established in a closed system where neither reactants nor products escape. Temperature constancy is not a requirement — equilibrium can exist at any temperature. A catalyst and high pressure affect rate or position but are not prerequisites for equilibrium itself.
Q19Relation between Kp and Kc
For a gaseous equilibrium reaction, which expression correctly relates Kp and Kc?
Not quite — the answer is A.
Kp = Kc(RT)^Δn where R is the gas constant, T is temperature in Kelvin, and Δn is the change in moles of gaseous species. Option D inverts the exponent incorrectly. Option B omits Δn entirely.
Q20Effect of Temperature Pressure Concentration
For which of the following reactions is Kp equal to Kc?
Not quite — the answer is B.
Kp = Kc(RT)^Δn; Kp = Kc only when Δn = 0. For H₂ + I₂ ⇌ 2HI, Δn = 2−2 = 0. All other options have Δn ≠ 0. Option A (Δn = −2), C (Δn = +1), D (Δn = −1).
Q21Acids Bases and Salts
According to the Arrhenius concept, a base is a substance that:
Not quite — the answer is B.
Arrhenius bases increase [OH⁻] in aqueous solution. Option A defines an Arrhenius acid — the primary distractor. Options C and D belong to Brønsted–Lowry and Lewis theories respectively.
Q22Hydrolysis of Salts
Salt hydrolysis is best defined as:
Not quite — the answer is A.
Hydrolysis = interaction of cation or anion of a salt with water to regenerate the acid or base it came from. Option C (ionisation) is a trap — dissolution and hydrolysis are different processes; NaCl dissolves but does not hydrolyse. Option D confuses hydrolysis with neutralisation.
Q23Equilibrium in Physical Processes
In a closed container, water establishes equilibrium with its vapour. Which statement is correct?
Not quite — the answer is B.
At dynamic equilibrium both evaporation and condensation continue simultaneously at equal rates — the system is not static. Option A is the most common wrong choice: rates do not become zero; they become equal.
Q24Equilibrium in Physical Processes
Which of the following represents phase equilibrium?
Not quite — the answer is C.
Phase equilibrium involves the same substance existing in two different phases — H2O(l) ⇌ H2O(g) is liquid-vapour equilibrium. Option D is a common trap: though it involves solids and gas, CaCO3 decomposition is a chemical equilibrium involving different substances, not a phase change.
ELITE question · AIR under 50 level
This chapter has 278 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Equilibrium Concepts
Quick revision: most questions in this chapter test these facts.
| Concept | Key Fact |
|---|---|
| Kc and Kp | Kp = Kc(RT)^Δn; large K → products favoured; K is temperature-dependent only |
| Le Chatelier | System shifts to oppose the change — pressure, concentration or temperature |
| pH | pH = −log[H⁺]; pOH = −log[OH⁻]; pH + pOH = 14 at 25°C |
| Buffer solutions | Resist pH change; acidic buffer = weak acid + conjugate base (e.g. CH₃COOH + CH₃COONa) |
| Ksp | Solubility product; precipitation occurs when ionic product > Ksp |
| Common ion effect | Adding a common ion decreases solubility of a sparingly soluble salt |
What the app covers in this chapter
698 questions in total, each with a detailed explanation.
| Important PYQ Mixed Concepts | 98 |
| Grand Test | 57 |
| Mixed Revision | 53 |
| Equilibrium in Physical Processes | 40 |
| Dynamic Nature of Equilibrium | 40 |
| Homogeneous and Heterogeneous Equilibria | 40 |
| Solubility Equilibrium Ksp | 39 |
| Law of Chemical Equilibrium (Law of Mass Action) | 37 |
| Grand Mixed High Difficulty | 37 |
| Ionic Equilibrium Introduction | 21 |
| Equilibrium Constant (Kc Kp) | 20 |
| Applications of Equilibrium Constant | 20 |
| Le Chatelier Principle | 20 |
| Ionization of Acids and Bases Ka Kb | 20 |
| pH Scale and Calculations | 20 |
| Buffer Solutions | 20 |
| Common Ion Effect | 20 |
| Overall Mixed Revision | 20 |
| Relation between Kp and Kc | 19 |
| Effect of Temperature Pressure Concentration | 19 |
| Acids Bases and Salts | 19 |
| Hydrolysis of Salts | 19 |
Questions students ask
Is Equilibrium important for NEET?
Very important — it is one of the highest-weightage Physical Chemistry chapters. pH calculations, Le Chatelier's principle, buffer solutions and Ksp problems appear every year.
Which topics should I revise first?
Master Kc/Kp relationship, Le Chatelier's principle with all three types of changes, pH and pOH calculations, buffer solution mechanism, and solubility product with common ion effect.
How many questions from this chapter are on RankUp?
The RankUp app has 698 questions on Equilibrium, including 278 ELITE questions. Every question has a detailed explanation.
