O Level / IGCSE Chemistry chapter 6: Chemical reactions MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
92 exam-style questions on Chemical reactions, 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. A catalyst is added to a reversible reaction in a closed system. What is the effect?
A
equilibrium is reached faster, but its position does not change
B
the position of equilibrium moves to the right, giving more product
C
only the rate of the forward reaction increases
D
the reaction stops being reversible
Show answer
Answer: A. A catalyst speeds up the forward and reverse reactions equally, so equilibrium is reached sooner with the same yield.
2. When 0.12 g of magnesium ribbon reacts with excess dilute hydrochloric acid, the volume of hydrogen collected reaches a final value of 120 cm3 at room conditions. The experiment is repeated with 0.06 g of magnesium powder and the same acid. What is the final volume of hydrogen?
A
30 cm3
B
60 cm3
C
120 cm3
D
240 cm3
Show answer
Answer: B. The acid is in excess, so the volume of hydrogen depends only on the amount of magnesium: half the mass gives half the volume, 60 cm3. Powder makes the gas come off faster but does not change the final volume.
3. In a burning candle, solid wax first melts and then the molten wax burns. Which statement is correct?
A
melting is a chemical change and burning is a physical change
B
both are chemical changes
C
both are physical changes
D
melting is a physical change and burning is a chemical change
Show answer
Answer: D. Molten wax is still wax, so melting is physical. Burning produces carbon dioxide and water, which are new substances.
4. Blue hydrated copper(II) sulfate is heated and turns white. Adding water turns it blue again. What does this show?
A
the reaction is reversible
B
the reaction is irreversible
C
copper sulfate decomposes
D
water is a catalyst
Show answer
Answer: A. CuSO4·5H2O ⇌ CuSO4 + 5H2O: heating drives it forward, adding water reverses it. Anhydrous copper sulfate is the test for water.
5. What is the correct name of Cu2O, showing the oxidation number of copper?
A
copper(I) oxide
B
copper(II) oxide
C
copper(IV) oxide
D
copper(III) oxide
Show answer
Answer: A. Oxygen is −2, so two copper atoms total +2 and each is +1: copper(I) oxide. CuO is copper(II) oxide.
6. In the Contact process, sulfur dioxide reacts with oxygen: 2SO2(g) + O2(g) ⇌ 2SO3(g). What volume of oxygen exactly reacts with 120 dm3 of sulfur dioxide, both measured at the same temperature and pressure?
A
30 dm3
B
60 dm3
C
120 dm3
D
240 dm3
Show answer
Answer: B. Equal volumes of gases contain equal numbers of moles, and the mole ratio SO2 : O2 is 2 : 1, so 120 ÷ 2 = 60 dm3. 240 dm3 uses the ratio upside down.
7. Which substance undergoes only a physical change when it is heated?
A
iodine crystals
B
calcium carbonate
C
magnesium ribbon in air
D
copper(II) carbonate
Show answer
Answer: A. Iodine sublimes to a vapour and turns back to crystals on cooling; it is still iodine. The carbonates decompose and magnesium burns, forming new substances.
8. The rate of which reaction could not be followed by measuring the loss in mass of the reaction flask on a balance?
A
calcium carbonate with dilute hydrochloric acid
B
magnesium carbonate with dilute nitric acid
C
hydrogen peroxide solution with a manganese(IV) oxide catalyst
D
aqueous sodium hydroxide with dilute hydrochloric acid
Show answer
Answer: D. Mass is lost only if a gas escapes. Neutralisation of sodium hydroxide by hydrochloric acid forms only a salt and water, so the mass stays the same; the other three give off CO2 or O2.
9. Water can be boiled to form steam, or electrolysed to form hydrogen and oxygen. Which statement is correct?
A
both are chemical changes, because water is used up in each process
B
boiling is a chemical change because bonds break, and electrolysis is a physical change
C
both are physical changes, because water is the same before and after
D
electrolysis is a chemical change because new substances form; boiling is a physical change
Show answer
Answer: D. Steam is still H2O, so boiling is physical. Electrolysis breaks water down into new substances, so it is chemical.
10. What is a catalyst?
A
a substance that slows down a reaction and is used up in doing so
B
a substance that is used up during a reaction and speeds it up
C
a substance that speeds up a reaction and is unchanged at the end
D
a substance that raises the yield by shifting the equilibrium position
Show answer
Answer: C. A catalyst speeds up a reaction by providing a route with a lower activation energy and is chemically unchanged at the end.
92, each with the answer and a short explanation, across 4 topics: Physical and chemical changes, Rate of reaction, Reversible reactions and equilibrium, Redox. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Chemistry chapter 6 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.
