The Rate and Extent of Chemical Change | AQA GCSE Chemistry, Higher tier (8462)
The Rate and Extent of Chemical Change
- 150 questions
- 10 subtopics
- Paper 2
- Paper 2
The Rate and Extent of Chemical Change is examined in Chemistry Paper 2.
It covers measuring the mean rate of a reaction, rate from graphs, and the gradient of a tangent, factors which affect the rates of chemical reactions, collision theory and activation energy, catalysts, reversible reactions and dynamic equilibrium, the effect of changing conditions on equilibrium, the effect of changing concentration, the effect of temperature changes on equilibrium and the effect of pressure changes on equilibrium.
Sample questions from The Rate and Extent of Chemical Change
Answer each one closed book first, then open the answer.
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Measuring the mean rate of a reaction
A reaction uses up 2.4 g of magnesium in 60 s. Calculate the mean rate of reaction.
Show the answer
2.4 g ÷ 60 s = 0.04 g/s. -
Rate from graphs, and the gradient of a tangent
Two reactions are followed on the same axes of gas volume against time. State how you can tell from the curves which reaction is faster at the start.
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The reaction whose curve is steeper at the start is the faster one. -
Factors which affect the rates of chemical reactions
State the effect on the rate of reaction of using a powdered solid in place of a single lump of the same mass.
Show the answer
The rate of reaction increases. -
Collision theory and activation energy
Explain the two reasons why raising the temperature increases the rate of a reaction.
Show the answer
The particles move faster so they collide more frequently, and a greater proportion of the collisions have at least the activation energy. -
Catalysts
Explain why enzymes are described as catalysts.
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They speed up reactions in biological systems and are not used up by those reactions. -
Reversible reactions and dynamic equilibrium
State what has to be altered to change the direction in which a reversible reaction goes.
Show the answer
The conditions, such as the temperature, must be changed. -
The effect of changing conditions on equilibrium
State whether an equilibrium mixture returns to exactly its original composition after a condition has been changed.
Show the answer
No, it settles at a new equilibrium in which the relative amounts of reactants and products are different. -
The effect of changing concentration
State and explain what happens to the amount of product when the concentration of a reactant is increased.
Show the answer
More product is formed until equilibrium is reached again, because the system shifts towards the products to use up the added reactant.
The 10 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Measuring the mean rate of a reaction | Following the quantity of reactant used or product formed over time, using a balance for a gas-producing reaction, the mean rate equations, worked calculations, and the units g/s and cm³/s. | 13 |
| Rate from graphs, and the gradient of a tangent | Rate in mol/s, the shape of a volume against time graph and what a horizontal section means, drawing a tangent to find the rate at one moment and calculating its gradient, why a curve is steepest at the start and flattens, plotting graphs with a line of best fit, y = mx + c, gradients and intercepts, and direct proportionality. | 24 |
| Factors which affect the rates of chemical reactions | The five factors that affect rate, the effects of concentration, temperature, surface area, gas pressure and catalysts, investigating concentration by gas volume and by the disappearing cross, why rate is proportional to one over the time taken, identifying variables, and writing a hypothesis. | 15 |
| Collision theory and activation energy | The two conditions for colliding particles to react and activation energy, what collision theory explains, why higher concentration, gas pressure, surface area and temperature make collisions more frequent or more energetic, surface area to volume ratio, predicting rate changes when conditions are altered, and the symbols for proportionality, much less than, much greater than and approximately. | 22 |
| Catalysts | What a catalyst is and why little is needed, why different reactions need different catalysts, enzymes as biological catalysts, how a catalyst provides a pathway with lower activation energy without changing the amount of product or the energy change, its effect on a reaction profile, identifying one, and industrial uses. | 14 |
| Reversible reactions and dynamic equilibrium | Reversible reactions and the ⇌ symbol, forward and reverse reactions and changing direction by altering conditions, heating and rehydrating copper sulfate, equal energy transferred in each direction, the closed system needed for equilibrium, and equilibrium as forward and reverse reactions continuing at the same rate. | 15 |
| The effect of changing conditions on equilibrium | How conditions fix the relative amounts at equilibrium, how a system counteracts a change, Le Chatelier's Principle, what a position lying to the right means, and the ammonia equilibrium under changes of temperature, pressure and concentration. | 12 |
| The effect of changing concentration | What happens to a mixture when one concentration changes, why the whole system shifts, the effects of adding a reactant or removing or adding a product, and the hydrogen iodide and ammonia equilibria as examples. | 12 |
| The effect of temperature changes on equilibrium | Why raising the temperature shifts an equilibrium in the endothermic direction and lowering it in the exothermic direction, the effect on yield for each type of forward reaction, ammonia and N₂O₄ as examples, and the compromise industrial temperature. | 12 |
| The effect of pressure changes on equilibrium | Which equilibria respond to pressure and why solutions do not, shifting towards fewer or more molecules, counting gas molecules from balancing numbers, and predictions for the ammonia, sulfur dioxide, N₂O₄ and hydrogen iodide equilibria. | 11 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
AQA GCSE Chemistry, Higher tier Active Recall Guide
Every topic, not just this one. 1,648 questions with their answers.