AS Level Chemistry chapter 7: Equilibria MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
48 exam-style questions on Equilibria, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. In aqueous solution: 2CrO42−(aq) (yellow) + 2H+(aq) ⇌ Cr2O72−(aq) (orange) + H2O(l). Aqueous sodium hydroxide is added to an orange equilibrium mixture. What is observed?
A
there is no change, because Na+ and OH− do not appear in the equation
B
the solution turns a deeper orange, because OH− removes H+ and the equilibrium moves to the right
C
the solution turns yellow, because OH− removes H+ and the equilibrium moves to the left
D
the solution turns yellow, because OH− reduces the dichromate ions
Show answer
Answer: C. OH− reacts with H+ to form water, lowering [H+]; the equilibrium moves left to replace H+, forming yellow CrO42−. No redox occurs (Cr stays +6).
2. An equilibrium mixture contains 2.0 mol of N2, 6.0 mol of H2 and 2.0 mol of NH3 at a total pressure of 200 kPa. What is the partial pressure of hydrogen?
A
60 kPa
B
150 kPa
C
40 kPa
D
120 kPa
Show answer
Answer: D. Total amount = 10.0 mol, so the mole fraction of H2 = 6.0/10.0 = 0.60. Partial pressure = mole fraction × total pressure = 0.60 × 200 = 120 kPa.
3. Which list contains only alkalis?
A
NaOH, KOH, NH3
B
NaOH, HNO3, KOH
C
NH4Cl, KOH, NaOH
D
CH3COOH, NaOH, NH3
Show answer
Answer: A. Sodium hydroxide, potassium hydroxide and ammonia all give OH− ions in water. HNO3 and CH3COOH are acids, and NH4Cl is a salt (NH4+ is a proton donor).
4. N2O4(g) ⇌ 2NO2(g) is at equilibrium. The total pressure is increased at constant temperature. What happens to the position of equilibrium and to the value of Kp?
A
the position moves to the left; Kp does not change
B
the position moves to the right; Kp decreases
C
the position moves to the left; Kp increases
D
the position moves to the right; Kp does not change
Show answer
Answer: A. Higher pressure favours the side with fewer gas moles (1 mol N2O4 on the left). Only temperature changes Kp, so Kp stays the same.
5. Which statement about 0.1 mol dm−3 hydrochloric acid and 0.1 mol dm−3 ethanoic acid is correct?
A
both have the same pH because they have the same concentration
B
hydrochloric acid has the lower pH and the higher electrical conductivity because it is fully dissociated
C
ethanoic acid has the lower pH because it contains more hydrogen atoms
D
ethanoic acid does not react with magnesium
Show answer
Answer: B. HCl is a strong acid, so 0.1 mol dm−3 gives 0.1 mol dm−3 of H+ (pH 1) and many ions to carry current. Ethanoic acid is only partly dissociated (pH about 3), so it reacts more slowly with magnesium but still reacts.
6. A gas mixture contains 8.0 g of oxygen, O2, and 14.0 g of nitrogen, N2, at a total pressure of 120 kPa. What is the partial pressure of oxygen?
A
40 kPa
B
43.6 kPa
C
60 kPa
D
80 kPa
Show answer
Answer: A. n(O2) = 0.25 mol and n(N2) = 0.50 mol, so the mole fraction of O2 is 1/3 and p(O2) = 120/3 = 40 kPa. 43.6 kPa uses the mass fraction; 80 kPa is the partial pressure of nitrogen.
7. For the gaseous equilibrium X ⇌ 2Y, the percentage of Y in the equilibrium mixture at constant pressure is 60% at 300 °C and 35% at 500 °C. Which deduction is correct?
A
the forward reaction is endothermic and Kc increases as the temperature rises
B
the forward reaction is endothermic and Kc decreases as the temperature rises
C
the forward reaction is exothermic and Kc decreases as the temperature rises
D
the forward reaction is exothermic and Kc does not change with temperature
Show answer
Answer: C. Less Y at a higher temperature means raising the temperature favours the reverse (endothermic) direction, so the forward reaction is exothermic and Kc falls as temperature rises.
8. Hydrogen chloride gas and ammonia gas react to form a white solid: HCl(g) + NH3(g) → NH4Cl(s). Which statement is correct?
A
NH3 acts as a Brønsted–Lowry acid because it gains a proton
B
HCl acts as a Brønsted–Lowry base because it loses a proton
C
it is an acid–base reaction because HCl donates a proton to NH3
D
it is not an acid–base reaction because no water is present
Show answer
Answer: C. The Brønsted–Lowry theory is about proton transfer and does not need water: HCl is the proton donor (acid) and NH3 the proton acceptor (base).
9. 25.0 cm3 of 0.100 mol dm−3 hydrochloric acid and 25.0 cm3 of 0.100 mol dm−3 ethanoic acid are each titrated with 0.100 mol dm−3 sodium hydroxide. Which statement is correct?
A
ethanoic acid needs less NaOH because it is only partially dissociated
B
both need 25.0 cm3, because as OH− removes H+ more ethanoic acid dissociates until it has all reacted
C
ethanoic acid needs more NaOH because its pH is higher
D
hydrochloric acid needs 50.0 cm3 because it is a strong acid
Show answer
Answer: B. Both contain 2.50 × 10−3 mol of monobasic acid. Partial dissociation affects pH and rate, not the total amount of acid available to react, so both need 25.0 cm3.
10. 1.0 mol of A and 1.0 mol of B are placed in a 2.0 dm3 vessel. At equilibrium for A + B ⇌ C, 0.40 mol of C is present. What is Kc?
A
0.44 dm3 mol−1
B
1.11 dm3 mol−1
C
2.22 dm3 mol−1
D
4.44 dm3 mol−1
Show answer
Answer: C. At equilibrium A = B = 1.0 − 0.40 = 0.60 mol. Concentrations (÷ 2.0 dm3): A = B = 0.30, C = 0.20 mol dm−3. Kc = 0.20/(0.30 × 0.30) = 2.22 dm3 mol−1. Using moles instead of concentrations gives 1.11.
48, each with the answer and a short explanation, across 2 topics: Chemical equilibria: reversible reactions, dynamic equilibrium, Brønsted–Lowry theory of acids and bases. Every chapter test draws ten of them, so you can take it many times.
Is the AS Level Chemistry chapter 7 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
