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Most Repeated MDCAT Chemistry: Chemical Equilibrium MCQs
The most repeated Chemical Equilibrium questions in MDCAT Chemistry, measured from 377 real past papers. Chemical Equilibrium contributed 337 questions across those papers, and 8 distinct questions recurred with the same verified answer across 2 or more different exam years — listed below (ranked by how many years each recurs in), with the answer, an explanation, and the exact years.
Measured from 377 real past papers · updated July 2026
Why Chemical Equilibrium is a high-yield MDCAT Chemistry topic
Out of 337 real Chemistry questions attributed to Chemical Equilibrium across 377 MDCAT past papers, 8 distinct questions came back with the same correct answer in 2 or more different exam years (the recurrences here span 2009–2024, 9 distinct exam years). A question the examiners have reused verbatim is far more likely to appear again than one asked only once — which is exactly why working through this list first is one of the highest-return ways to revise MDCAT Chemistry.
Most repeated in this topic
“When 18 ×10-3 moles/dm3 of acetic acid react with 22×10-3 moles/dm3 of ethyl alcohol to form 40×10-3 moles/dm3 of ethyl acetate and 40×10-3 moles/dm3 of waterFind the value of equilibrium constant (Kc)”
Appeared in 2 exam years (2009, 2010) — always with the same answer. It is the first question below.
How to use this list
Every question below shows the verified correct answer, a short explanation, and the exact past-paper years it appeared in — with the most-repeated ones first. Read the explanation even when you know the answer, since MDCAT often reuses the concept with reworded options. When you have these 8 down cold, drill the full topic with fresh questions in the MDCAT MCQ practice bank, then revise the underlying theory in the Chemical Equilibrium chapter guide.
How we measured “most repeated”
We parsed 377 real MDCAT past papers and grouped questions that are effectively the same. A question counts as repeated only when the same correct answer recurs in 2 or more distinct exam years — not merely a similar topic or a lucky guess. Questions that appeared only once are excluded, so nothing here is padding. See the full method and subject-by-subject numbers on the MDCAT repetition study.
- 1Repeated in 2 yearsChemical Equilibrium
When 18 ×10-3 moles/dm3 of acetic acid react with 22×10-3 moles/dm3 of ethyl alcohol to form 40×10-3 moles/dm3 of ethyl acetate and 40×10-3 moles/dm3 of waterFind the value of equilibrium constant (Kc)
- A4.04✓
- B3.14
- C3.04
- D2.02
- E1.04
Explanation
Kc= Concentration of products / Concentration of Reactants. Reactants = acetic acid and ethyl alcohol Products = ethyl acetate and water Multiplication product of products (40 × 40 =1600) Divide by multiplication product of reactants (18× 22= 396) 1600/396= 4.04.
Appeared in the past papers of: 2009, 2010
- 2Repeated in 2 yearsChemical Equilibrium
In the Haber process for manufacturing of ammonia, Nitrogen is taken from:
- AProteins occurring in living bodies
- BAmmonium salts obtained industrially
- CAir✓
- DMinerals containing nitrates
Explanation
In the Haber process, Nitrogen is obtained from the air, which contains about 78% nitrogen gas. The air is compressed and then passed through a catalyst bed along with hydrogen gas at a high temperature and pressure. The nitrogen gas reacts with hydrogen gas in the presence of an iron catalyst to form ammonia gas. Haber process is an important industrial process for the production of ammonia, which is a key component in the manufacture of fertilizers, explosives, and other chemical compounds.
Appeared in the past papers of: 2011, 2012
- 3Repeated in 2 yearsChemical Equilibrium
Which of the following reactions has the same value of Kc and Kp?
- AN2+ 3H2 ⇌ 2NH3
- BPCI5 ⇌ PCI3 +CI2
- CH2 + I2 ⇌ 2HI✓
- D2SO2 + O2 ⇌ 2SO3
Appeared in the past papers of: 2023, 2024
- 4Repeated in 2 yearsChemical Equilibrium
Which of the following conditions is required for maximum yield of ammonia through Haber's process?
- AIncreasing temperature
- BDecreasing concentration of reactant
- CDecreasing Pressure
- DDecreasing temperature✓
Explanation
The reaction between N2 and H2 to give NH3 is exothermic. N2 + 3H2 → 2NH3 ΔH = -92.46KJ/mol. Hence, the yield of ammonia can be increased by decreasing temperature as in exothermic reactions decrease in temperature favors forward reaction i.e, yield of ammonia in this case. The yield of ammonia can also be increased by increasing pressure or removing the product continuously. Hence, option D is correct.
Appeared in the past papers of: 2023, 2024
- 5Repeated in 2 yearsChemical Equilibrium
Which of the following is true for a reversible reaction at equilibrium?
- AThe rate of forward reaction is greater than backward reaction
- BThe rate of forward reaction is lesser than backward reaction
- CThe rate of backward reaction is equal to forward reaction✓
- DThe rate of backward reaction is greater than forward reaction
Explanation
At equilibrium state, the rate of backward reaction becomes equal to rate of forward reaction. STB Pg- 165. Hence, option C is correct.
Appeared in the past papers of: 2023, 2024
- 6Repeated in 2 yearsChemical Equilibrium
For a gaseous phase reaction, when number of moles of reactants and products are equal:
- AThe values of Kp and Kc are different
- BThe value of Kp is greater than Kc
- CThe value of Kc is greater than Kp
- DThe values of Kp and Kc are the same✓
Explanation
If the difference in n is zero, the Kp = Kc.
Appeared in the past papers of: 2020, 2023
- 7Repeated in 2 yearsChemical Equilibrium
For the reaction N2 + O2 2NO, the value of K is 0.0842 at 3500 K. Calculate the fraction of equilibrium mixture of N2 and O2 converted into NO.
- A15.0%
- B16.3%
- C16.5%
- D16.9%✓
Explanation
Let's assume that x represents the fraction of N2 and O2 converted into NO. Therefore, at equilibrium, the concentrations can be expressed as:[NO] = 2x, [N2] = (1 - x), [O2] = (1 - x)Substituting these values into the equilibrium constant expression:K = (2x)^2 / ((1 - x) * (1 - x))Simplifying the equation:0.0842 = 4x^2 / (1 - 2x + x^2) Rearranging the equation:0.0842(1 - 2x + x^2) = 4x^20.0842 - 0.1684x + 0.0842x^2 = 4x^20.0842x^2 + 4x^2 - 0.1684x - 0.0842 = 0Combining like terms:4.0842x ^2 - 0.1684x - 0.0842 = 0This is a quadratic equation.
Appeared in the past papers of: 2014, 2015
- 8Repeated in 2 yearsChemical Equilibrium
The equation N (g) + 3H (g) ⇋ 2NH (g) represents:
- AContact process
- BHaber process✓
- CSolvay’s process
Explanation
The reaction combines nitrogen and hydrogen to form ammonia (NH₃). This industrial method is specifically known as the Haber’s process. It is different from the Contact process (for H₂SO₄) and Solvay process (for Na₂CO₃).
Appeared in the past papers of: 2020, 2023