GCSE Chemistry (AQA) chapter 6: The rate and extent of chemical change MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
36 exam-style questions on The rate and extent of chemical change, 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.
4.6.1 Calculating and measuring rates of reaction10 questions
4.6.1 Factors affecting rate, collision theory and catalysts15 questions
4.6.2 Reversible reactions and dynamic equilibrium11 questions
Ten The rate and extent of chemical change questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. H2(g) + I2(g) ⇌ 2HI(g). What is the effect of increasing the pressure on the equilibrium amount of HI?
A
it increases, because the higher pressure favours the forward reaction
B
it doubles, because the pressure has doubled
C
it decreases, because the higher pressure pushes the reaction back to the reactants
D
it is unchanged, because both sides have the same number of gas molecules
Show answer
Answer: D. There are 2 gas molecules on each side, so pressure does not favour either direction. The rate still increases.
2. Heating blue hydrated copper(II) sulfate forms white anhydrous copper(II) sulfate and water. What happens when water is added back to the white solid?
A
it turns blue and the temperature rises
B
it stays white and the temperature rises
C
it turns green and the temperature falls
D
it turns blue and the temperature falls
Show answer
Answer: A. The forward reaction is endothermic, so the reverse is exothermic by the same amount: the solid turns blue again and warms up.
3. The concentration of a reactant in solution is doubled and the temperature is kept the same. Which statement is correct?
A
the frequency of collisions doubles, but the proportion of collisions with enough energy is unchanged
B
the frequency of collisions doubles, and the activation energy is halved
C
the frequency of collisions doubles, and twice as large a proportion of collisions are successful
D
the frequency of collisions is unchanged, but each particle has twice as much energy
Show answer
Answer: A. Twice as many particles in the same volume means about twice as many collisions per second. The energy of the particles and the activation energy depend on temperature and catalysts, not concentration, so the proportion of successful collisions stays the same.
4. Why does increasing the pressure of a reacting gas mixture increase the rate?
A
the same particles are squeezed closer together, so collisions are more frequent
B
the particles are moving faster, so more collisions have the activation energy
C
the activation energy of the reaction is lowered at high pressure
D
the gas particles have more energy because the container is squashed
Show answer
Answer: A. Higher pressure is like higher concentration: more particles per unit volume means more frequent collisions. It does not change particle speed at a fixed temperature.
5. In the same reaction, ammonia is removed from the equilibrium mixture as it forms. What is the effect?
A
the position shifts left to replace the ammonia that was removed
B
more ammonia is made as the equilibrium shifts right
C
the concentration of hydrogen rises as the ammonia is removed
D
the reaction stops because there is no product to react back
Show answer
Answer: B. Removing a product lowers its concentration, so the equilibrium shifts right to replace it. Nitrogen and hydrogen are used up.
6. Why is the gradient of a product-against-time graph greatest at the start of a reaction?
A
the catalyst is most active at the start, before it is used up
B
the activation energy is lowest at the start of the reaction
C
the products that build up speed the reaction along as time goes on
D
the concentration of the reactant is highest, so collisions are most frequent
Show answer
Answer: D. As reactants are used up, their concentration falls, collisions become less frequent and the rate (gradient) decreases. A catalyst is not used up and the activation energy does not change during a reaction.
7. 2SO2(g) + O2(g) ⇌ 2SO3(g). The forward reaction is exothermic. What happens to the amount of SO3 at equilibrium when the temperature is increased?
A
it decreases, because the endothermic reverse reaction is favoured
B
it increases, because heat is added and the forward reaction takes in energy
C
it increases, because the higher temperature makes the forward reaction faster
D
it stays the same, because a change of temperature affects only the rate of reaction
Show answer
Answer: A. Raising the temperature favours the endothermic direction, which takes in energy. Here that is the reverse reaction, so less SO3.
8. An uncatalysed reaction has reactants at 0 kJ/mol, a peak at +150 kJ/mol and products at −90 kJ/mol. A catalyst lowers the peak to +100 kJ/mol. Which shows the activation energy and overall energy change for the catalysed reaction?
A
activation energy +100 kJ/mol; overall energy change −90 kJ/mol
B
activation energy +100 kJ/mol; overall energy change −140 kJ/mol
C
activation energy +50 kJ/mol; overall energy change −90 kJ/mol
D
activation energy +190 kJ/mol; overall energy change −40 kJ/mol
Show answer
Answer: A. Activation energy = peak − reactants = 100 − 0 = +100 kJ/mol. A catalyst does not change the energies of the reactants or products, so the overall energy change stays at −90 kJ/mol. 50 kJ/mol is only the amount the catalyst lowered the peak by.
9. Why does raising the temperature increase the rate of reaction?
A
the activation energy of the reaction decreases because the particles are hotter and more energetic
B
more reactant particles are made, so there are more particles in the same volume
C
the particles expand, so they are larger and collide more often with each other
D
particles move faster, so they collide more often and more collisions have the activation energy
Show answer
Answer: D. Temperature affects both collision frequency and collision energy; the second effect is the bigger one. The activation energy does not change.
10. Why can equilibrium be reached only in a closed system?
A
heat cannot enter from the surroundings, so the reaction stays exothermic
B
the pressure inside always stays high enough for the reaction to work
C
a catalyst can work more effectively on the reactants
D
reactants and products cannot escape from the reaction vessel
Show answer
Answer: D. If a product such as a gas escapes, the reverse reaction cannot happen at the same rate, so the system never reaches equilibrium.
The rate and extent of chemical change: questions students ask
How many The rate and extent of chemical change MCQs are there?
36, each with the answer and a short explanation, across 3 topics: 4.6.1 Calculating and measuring rates of reaction, 4.6.1 Factors affecting rate, collision theory and catalysts, 4.6.2 Reversible reactions and dynamic equilibrium. Every chapter test draws ten of them, so you can take it many times.
Is the GCSE Chemistry (AQA) 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.
