Le Chatelier's Principle

Le Chatelier's Principle MDCAT MCQs with answers

15 past paper MCQs on Le Chatelier's Principle, from the Chemical Equilibrium unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.For a gaseous reaction, an increase in pressure will shift the equilibrium in the direction of: (MDCAT 2020)

  1. decreased concentration
  2. increased concentration
  3. decreased volume
  4. increased volume
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Correct answer: (c) decreased volume

The system relieves the pressure by moving to the side with fewer gas molecules, which occupies less volume.

2.In the reaction $\mathrm{H_2+CO_2\rightleftharpoons H_2O+CO}$, a decrease in the concentration of $\mathrm{CO_2}$ will shift the equilibrium: (MDCAT 2020)

  1. towards the left
  2. towards the right
  3. nothing happens to the equilibrium
  4. towards both directions
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Correct answer: (a) towards the left

Taking a reactant away makes the reverse reaction the faster of the two, so the equilibrium moves back to the left.

3.When the numbers of moles of reactants and products are equal in a reversible gaseous reaction, which parameter would not affect the equilibrium? (MDCAT 2020)

  1. temperature
  2. pressure
  3. concentration
  4. catalyst
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Correct answer: (b) pressure

With no change in the number of gas molecules there is no volume change for the pressure to act on.

4.One can estimate the direction in which an equilibrium will shift with the help of: (MDCAT 2022)

  1. Le Chatelier's principle
  2. the law of mass action
  3. Hess's law
  4. the law of heat of formation
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Correct answer: (a) Le Chatelier's principle

The system responds so as to reduce the change imposed on it, which is Le Chatelier's principle.

5.One can estimate the direction in which an equilibrium will shift with the help of: (MDCAT 2023)

  1. Le Chatelier's principle
  2. the law of mass action
  3. Hess's law
  4. the law of heat of formation
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Correct answer: (a) Le Chatelier's principle

Le Chatelier's principle says the system shifts so as to oppose the change imposed on it.

6.The principle which states that if a stress is applied to a system at equilibrium the system nullifies the effect of the stress as far as possible is: (MDCAT 2024)

  1. Haber's
  2. Le Chatelier's
  3. Boyle's
  4. Charles'
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Correct answer: (b) Le Chatelier's

That is Le Chatelier's principle.

7.Consider the following reaction in equilibrium and tell which chemical, when added, will change the cloudy solution into a clear solution: $\mathrm{BiCl_3+H_2O\rightleftharpoons BiOCl+2HCl}$ (MDCAT 2024)

  1. $\mathrm{BiCl_3}$
  2. $\mathrm{H_2O}$
  3. $\mathrm{BiOCl}$
  4. $\mathrm{HCl}$
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Correct answer: (d) $\mathrm{HCl}$

Added HCl drives the equilibrium back to the left, so the insoluble BiOCl that clouded the solution dissolves.

8.If ΔH for a reaction is positive, then by decreasing temperature, the reaction will (KMU MDCAT 2025)

  1. Move forward
  2. Move in reverse
  3. Have no effect
  4. Be both forward and reverse
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Correct answer: (b) Move in reverse

The forward reaction absorbs heat, so cooling shifts the equilibrium back the other way.

9.For which reaction, the value of Kc increases with increase in temperature? (SIBA MDCAT 2025)

  1. CH4 + O2 → CO2 + H2O
  2. NaOH + HCl → NaCl + H2O
  3. 2SO2 + O2 → 2SO3
  4. H2 + I2 → 2HI
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Correct answer: (d) H2 + I2 → 2HI

Only the formation of hydrogen iodide from its elements absorbs heat, and heating favours the endothermic direction.

10.In separate vessel of volume 2000 cm3 and 1500cm3, 6g of hydrogen and 28g of nitrogen are mixed in each vessel at 25°C, ammonia formed is? N2 + 3H2 ⇌ 2NH3 (SZABMU MDCAT 2025)

  1. More in 2 L vessel
  2. More in 1500 cm^3 vessel
  3. Equal in both vessel
  4. Cannot be predicted
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Correct answer: (b) More in 1500 cm^3 vessel

The forward reaction goes from four molecules to two, so the smaller vessel, at higher pressure, gives more ammonia.

11.The principle that states that if a stress is applied to a system at equilibrium the system nullify the effect of stress as far as possible is: (UHS MDCAT 2024)

  1. Haber's
  2. Le-Chatelier
  3. Boyle's
  4. Charles'
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Correct answer: (b) Le-Chatelier

That is Le Chatelier’s principle.

12.Consider the following reaction in equilibrium and tell addition of which chemical will turn the cloudy solution into clear solution? BiCl3 + H2O <-> BiOCl + 2HCl (UHS MDCAT 2024)

  1. BiCl3
  2. H2O
  3. BiOCl
  4. HCl
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Correct answer: (d) HCl

Adding hydrochloric acid drives the equilibrium back and dissolves the white bismuth oxychloride.

13.In the production of SO3 from SO2 and Oxygen, the yield of SO3 is increased by (KMU MDCAT 2024)

  1. Adding a catalyst
  2. Adding more SO2
  3. Increasing temperature
  4. Removing oxygen
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Correct answer: (b) Adding more SO2

Adding more of a reactant drives the equilibrium towards the product.

14.Q.85 One can estimate the direction in which equilibrium will shift with the help of: (UHS MDCAT 2023)

  1. Le Chatelier's principle
  2. Law of mass action
  3. Mess's law
  4. Law of heat of formation
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Correct answer: (a) Le Chatelier's principle

Le Chatelier’s principle says which way an equilibrium moves when it is disturbed.

15.In reversible reaction, when product is removed, the equilibrium shift towards the: (UHS MDCAT 2023)

  1. Reactant side
  2. Product side
  3. Both side one by one
  4. No effect
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Correct answer: (b) Product side

Taking the product away drives the equilibrium forward to replace it.

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