The law of mass action states that the rate of a reaction is proportional to ____
Correct answer B. the product of the active masses of the reactants
Topic / 40 questions
Chemical Equilibrium MCQs
Chemical Equilibrium MCQs are multiple-choice questions on reversible reactions, equilibrium constants, Le Chatelier's principle, solubility product, the common ion effect and buffer solutions. They follow the MDCAT chemistry curriculum, and every question on MCQs360 shows its correct answer instantly so you can check each calculation straight away.
- Gases 40
- Liquids 40
- Solids 40
- Chemical Equilibrium 40
- Reaction Kinetics 40
- Thermochemistry and Energetics 40
- Electrochemistry 40
- Fundamental Concepts of Chemistry 40
- Atomic Structure 39
- Chemical Bonding 39
- Alcohols and Phenols 38
- Industrial Chemistry 37
- Aldehydes and Ketones 37
- Alkyl Halides 37
- s- and p-Block Elements 37
- Chemistry of Hydrocarbons 36
- Fundamental Principles of Organic Chemistry 36
- Carboxylic Acids 36
- Transition Elements 35
- Macromolecules 35
What is the effect of increasing pressure on the equilibrium N₂(g) + O₂(g) ⇌ 2NO(g)?
Correct answer B. No effect on the equilibrium position
The Ksp of Mg(OH)₂ is 4.0 × 10⁻¹² mol³ dm⁻⁹. What is its molar solubility?
Correct answer B. 1.0 × 10⁻⁴ mol dm⁻³
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The Ksp of AgBr is 4.9 × 10⁻¹³ mol² dm⁻⁶. What is its molar solubility in pure water?
Correct answer B. 7.0 × 10⁻⁷ mol dm⁻³
Why does pure NaCl crystallise out when HCl gas is passed into a saturated solution of crude common salt?
Correct answer C. The common Cl⁻ ion lowers the solubility of NaCl
In qualitative analysis, NH₄Cl is added before NH₄OH. What is the effect of the NH₄⁺ ion?
Correct answer A. It suppresses the ionisation of NH₄OH, lowering [OH⁻]
A buffer contains equal concentrations of NH₃ and NH₄Cl. If pKb of NH₃ is 4.74, what is the pH at 25 °C?
Correct answer D. 9.26
Which buffer system mainly maintains the pH of human blood at about 7.4?
Correct answer C. H₂CO₃ / HCO₃⁻
In an acidic buffer, if the concentration of the salt equals that of the weak acid, the pH of the buffer equals ____
Correct answer A. the pKa of the acid
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Which catalyst is used in the Haber process for the manufacture of ammonia?
Correct answer A. Finely divided iron with promoters
Which statement about the forward reaction N₂(g) + 3H₂(g) → 2NH₃(g) in the Haber process is correct?
Correct answer C. It is exothermic and decreases the number of gas molecules
N₂O₄(g) (colourless) ⇌ 2NO₂(g) (brown) is endothermic in the forward direction. What is seen when the equilibrium mixture is heated?
Correct answer B. The brown colour deepens
For N₂(g) + 3H₂(g) ⇌ 2NH₃(g) at equilibrium, what happens when more H₂ is added at constant volume and temperature?
Correct answer C. The equilibrium shifts forward and more NH₃ forms
For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), how is Kp related to Kc?
Correct answer C. Kp = Kc(RT)⁻²
1.0 mol of PCl₅ is heated in a 1.0 dm³ vessel and is 20% dissociated at equilibrium (PCl₅ ⇌ PCl₃ + Cl₂). What is Kc?
Correct answer A. 0.05 mol dm⁻³
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After mixing, a solution contains = 1.0 × 10⁻³ and = 1.0 × 10⁻³ mol dm⁻³. Given Ksp(BaSO₄) = 1.1 × 10⁻¹⁰, what happens?
Correct answer A. The ionic product is 1.0 × 10⁻⁶, so BaSO₄ precipitates
The equilibrium constant for A + B ⇌ C is Kc. What is the equilibrium constant for C ⇌ A + B at the same temperature?
Correct answer D. 1/Kc
In the Haber process, ammonia is liquefied and removed from the gas mixture. What is the effect on the equilibrium?
Correct answer C. The equilibrium shifts forward, producing more ammonia
At a given moment the reaction quotient Qc of a reaction is smaller than Kc. What will happen as the system moves to equilibrium?
Correct answer D. The net reaction proceeds in the forward direction
What does a very large value of Kc, such as 10¹², indicate about a reaction?
Correct answer D. At equilibrium the mixture consists mainly of products
About Chemical Equilibrium MCQs
The conceptual questions cover dynamic equilibrium in a closed system, writing Kc expressions and their units, and predicting how changes in concentration, pressure, temperature or a catalyst affect the position of equilibrium and the value of K. The Haber process for ammonia is used as the main industrial example of these ideas. The numerical questions deal with solubility product and the common ion effect, including molar solubility in a solution that already contains one of the ions and whether a precipitate will form. Buffer questions ask how acidic and basic buffers are made and use the Henderson–Hasselbalch equation to find pH.
Key facts to remember
- At dynamic equilibrium the forward and reverse reaction rates are equal and the concentrations of reactants and products stay constant.
- Le Chatelier's principle: if a system at equilibrium is disturbed, it shifts in the direction that tends to oppose the change.
- The equilibrium constant changes only with temperature; for an exothermic reaction, K decreases as temperature rises, and a catalyst does not change K.
- A precipitate forms when the ionic product of a sparingly soluble salt exceeds its Ksp; a common ion lowers the solubility of the salt.
- For an acidic buffer, pH = pKa + log([salt]/[acid]).
- The Haber process, N₂ + 3H₂ ⇌ 2NH₃ (ΔH = −92 kJ mol⁻¹), uses an iron catalyst at about 450 °C and 200 atm.
Exams that include Chemical Equilibrium MCQs
Pakistan
- MDCAT
- ECAT
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Chemical Equilibrium MCQs
- Practise working out the units of Kc from the balanced equation, since unit questions are quick marks.
- For each Le Chatelier question, decide first whether the change affects K or only the position of equilibrium.
- Learn the Henderson–Hasselbalch equation and the log values of 2, 3 and 10 for fast buffer pH calculations.
- In Ksp problems, write the dissolution equation and the expression for Ksp before substituting values.
Frequently asked questions
What does the MDCAT syllabus include in Chemical Equilibrium?
The PMDC MDCAT curriculum covers reversible reactions and dynamic equilibrium, Le Chatelier's principle for changes in concentration, pressure, temperature and catalyst, solubility product, the common ion effect, buffer solutions and their types, and the Haber process for ammonia.
Which exams ask Chemical Equilibrium MCQs?
Chemical equilibrium is tested in MDCAT, ECAT, NUMS and AKU entry tests and in FSc board papers in Pakistan, in NEET and JEE Main in India, and in HSC and medical admission tests in Bangladesh.
Does a catalyst change the position of equilibrium?
No. A catalyst speeds up the forward and reverse reactions equally, so equilibrium is reached faster, but the position of equilibrium and the value of the equilibrium constant stay the same. Only a change in temperature alters the equilibrium constant.
Last reviewed October 2026