Chemical Equilibrium

Chemical Equilibrium MDCAT MCQs with answers

15 past paper MCQs on Chemical Equilibrium, 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.

Read the notes first Practise the unit as a quiz

1.At equilibrium the concentrations of the reactants and the products become: (MDCAT 2020)

  1. zero
  2. equal
  3. constant
  4. infinite
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Correct answer: (c) constant

The two opposing rates are equal, so the concentrations stop changing, though they need not be equal to each other.

2.Chemical equilibrium is: (MDCAT 2023)

  1. the end of the reaction
  2. the complete consumption of the reactants
  3. the complete consumption of the products
  4. a state at which there is no net concentration change
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Correct answer: (d) a state at which there is no net concentration change

Both reactions continue at equal rates, so the concentrations stop changing without the reaction stopping.

3.If the equilibrium expression of a reversible reaction is [C]2/[A][B] The balanced chemical equation should be (SZABMU MDCAT 2025)

  1. C=A+B
  2. 2C=A+B
  3. A+B=C
  4. A + B = 2C
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Correct answer: (d) A + B = 2C

The powers in the expression are the coefficients, so two moles of C are formed from one of A and one of B.

4.Forward reaction is the one that (KMU MDCAT 2024)

  1. Is very slow at the beginning of the reaction
  2. Reacts to form reactants
  3. Speeds up gradually and at equilibrium its rate becomes constant
  4. Takes place from left to right as given in chemical equation
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Correct answer: (d) Takes place from left to right as given in chemical equation

The forward reaction is the one written from left to right in the equation.

5.The unit of Kc for the system PCl5 ⇌ PCl3 + Cl2 is (KMU MDCAT 2024)

  1. dm³/mol
  2. mol/ dm³
  3. mol/ dm⁶
  4. mol²/dm⁶
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Correct answer: (b) mol/ dm³

One concentration term is left over in the numerator, so the unit is moles per cubic decimetre.

6.By which of the following factors equilibrim state is attained earlier? (SZABMU MDCAT 2023)

  1. Temperature
  2. Pressure
  3. Concentration
  4. Catalyst
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Correct answer: (d) Catalyst

A catalyst speeds both directions equally, so equilibrium is reached sooner without being shifted.

7.By which of the following factors equilibrium state is attained earlier? (NUMS MDCAT 2023)

  1. Temperature
  2. Pressure
  3. Concentration
  4. Catalyst
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Correct answer: (d) Catalyst

A catalyst speeds both directions equally, so equilibrium comes sooner without moving.

8.What is the ultimate fate of reversible reaction? (UHS MDCAT 2023)

  1. Completion of reaction
  2. Complete consumption of reactants
  3. Complete consumption of products
  4. A state when there is no net concentration change
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Correct answer: (d) A state when there is no net concentration change

A reversible reaction ends in equilibrium, where the concentrations no longer change.

9.[Product]/[Reactant] = 2.5 for a reaction at equilibrium, what does it mean? (PMC MDCAT 2022)

  1. Products are more than reactants
  2. Products are Less
  3. reaction is at equilibrium
  4. Reactants are more
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Correct answer: (a) Products are more than reactants

A ratio above one means the equilibrium lies on the side of the products.

10.For a particular reversible reaction If [Products]/[Reactants]>Kc It means that: (PMC MDCAT 2022)

  1. More products are needed to attain equillbrium
  2. There are more reactants in the system
  3. More Reactants are needed to attain equillbrium
  4. The reaction will move forward to attain equilibrium
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Correct answer: (c) More Reactants are needed to attain equillbrium

The quotient is above the constant, so the reaction must run backwards to reach equilibrium.

11.The equilibrium constant is always written as a ratio of: (PMC Practice 2021)

  1. Reactants over products
  2. Products over reactants
  3. Product times Reactants
  4. None of these
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Correct answer: (b) Products over reactants

The equilibrium constant puts the products over the reactants, each to the power of its coefficient.

12.A very small value of Kc depicts: (PMC Practice 2021)

  1. No Reaction
  2. Backward Reaction
  3. Little Forward Reaction
  4. Complete Reaction
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Correct answer: (c) Little Forward Reaction

A small constant means the equilibrium lies well over towards the reactants.

13.If Kp and Kc have the same values then Δn will be: (PMC Practice 2021)

  1. Maximum
  2. Minimum
  3. Zero
  4. Negligible
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Correct answer: (c) Zero

$K_p=K_c(RT)^{\Delta n}$, so the two are equal only when $\Delta n$ is zero.

14.For a gaseous phase reaction, when number of moles of reactants and products are equal: (PMC MDCAT 2020)

  1. The values of Kp and Kc are different
  2. The value of Kp is greater than Kc
  3. The value of Kc is greater than Kp
  4. The values of Kp and Kc are the same
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Correct answer: (d) The values of Kp and Kc are the same

$K_p=K_c(RT)^{\Delta n}$, and with $\Delta n$ zero the two are equal.

15.Which of the following reaction has greater Kp than Kc? (PMC MDCAT 2020)

  1. 2NO + Cl2 2NOCl
  2. 2SO2 + O2 2SO3
  3. 2NOCl 2NO + Cl2
  4. N2 + 3H2 2NH3
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Correct answer: (c) 2NOCl 2NO + Cl2

$K_p=K_c(RT)^{\Delta n}$, and only that reaction goes from two molecules to three.

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