Cambridge IGCSE · Chemistry 0620
IGCSE Chemistry: Chemical reactions — Practice Questions & Answers
How fast reactions go, why conditions change rate, reversible reactions and equilibrium, plus redox by oxygen and electron transfer.
1336 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
Which change would increase the rate of a reaction between marble chips and dilute hydrochloric acid?
- Increasing the temperature
- Using larger marble chips
- Diluting the acid further
- Lowering the temperature
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WhyRaising the temperature gives particles more kinetic energy, so collisions are more frequent and more energetic, increasing the rate.
2
Multiple choice · Easy
What is a catalyst?
- A substance that increases reaction rate and is not used up
- A substance that is permanently consumed in the reaction
- A substance that always slows a reaction down
- A substance that changes the products formed
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WhyA catalyst speeds up a reaction without being used up, so it can be recovered chemically unchanged at the end.
3
Multiple choice · Easy
In terms of oxygen, oxidation is defined as the:
- gain of oxygen
- loss of oxygen
- gain of hydrogen
- gain of electrons
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WhyOxidation is gain of oxygen; the reverse, loss of oxygen, is reduction.
4
Multiple choice · Easy
Which symbol is used to show that a reaction is reversible?
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WhyThe double arrow <=> shows the reaction can proceed in both the forward and backward directions.
5
Multiple choice · Easy
Increasing the concentration of a reactant in solution increases the rate of reaction because there are:
- more frequent collisions between particles
- fewer collisions between particles
- particles with more activation energy
- larger particles colliding
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WhyMore particles in the same volume means more frequent collisions, so the rate increases.
6
Fill in the blank · Easy
In a redox reaction, the substance that is reduced is the agent.
Answer:
oxidising / oxidizing
WhyAn oxidising agent oxidises another substance and is itself reduced.
7
Multiple choice · Medium
A reaction is carried out using powdered zinc instead of zinc lumps, with all else kept the same. The rate increases because the powder has a:
- larger surface area for collisions
- higher activation energy
- greater concentration
- higher temperature
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WhyPowder has a larger surface area, so more particles are exposed for collisions, increasing the rate.
8
Multiple choice · Medium
In the reaction CuO + H2 -> Cu + H2O, which species is the reducing agent?
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WhyHydrogen removes oxygen from copper(II) oxide, so hydrogen is the reducing agent (it is itself oxidised).
9
Multiple choice · Medium
In terms of electron transfer, reduction is defined as the:
- gain of electrons
- loss of electrons
- gain of oxygen
- loss of hydrogen
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WhyReduction is gain of electrons; oxidation is loss of electrons (OIL RIG).
10
Multiple choice · Medium
A catalyst increases the rate of a reaction by:
- providing a pathway with lower activation energy
- increasing the activation energy
- raising the temperature of the mixture
- increasing the concentration of reactants
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WhyA catalyst provides an alternative pathway with a lower activation energy, so more collisions are successful.
Key terms in Chemical reactions
Rate of reaction: A measure of how quickly reactants are used up or products are formed over a given period of time.
Collision theory: The idea that particles must collide with sufficient energy and the correct orientation for a chemical reaction to occur.
Successful collision: A collision between particles that has enough energy and proper alignment to result in a reaction.
Activation energy: The minimum amount of energy that colliding particles must possess for a reaction to take place.
Frequency of collisions: How often reacting particles strike each other in a given time, which affects the reaction rate.
Concentration: The amount of a dissolved substance present in a fixed volume of solution.
Effect of concentration: Increasing the concentration of a reactant raises the rate by causing more frequent collisions between particles.
Pressure: The force exerted by gas particles per unit area on the walls of their container.
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