AQA · GCSE Chemistry 8462
AQA GCSE Chemistry: Energy changes — Practice Questions & Answers
Exothermic and endothermic reactions, reaction profiles, activation energy, bond energy sums, cells, batteries and fuel cells.
556 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 statement best describes an exothermic reaction?
- Energy is transferred from the reaction to the surroundings
- Energy is taken in from the surroundings
- No energy is transferred at all
- The surroundings always get colder
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WhyExothermic reactions transfer energy to the surroundings, usually as heat, so the temperature of the surroundings rises.
2
Multiple choice · Easy
Which of the following is an example of an exothermic process?
- Combustion of methane
- Thermal decomposition of calcium carbonate
- Citric acid reacting with sodium hydrogencarbonate
- Melting of ice
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WhyCombustion (burning) of fuels releases heat energy to the surroundings and is exothermic.
3
Multiple choice · Easy
In an endothermic reaction, the temperature of the surroundings usually:
- Decreases
- Increases
- Stays exactly the same
- Doubles
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WhyEndothermic reactions take in energy from the surroundings, so the surroundings lose heat and their temperature falls.
4
Multiple choice · Easy
On a reaction profile, the activation energy is the energy difference between:
- The reactants and the highest point of the curve
- The reactants and the products
- The products and the highest point of the curve
- Two different products
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WhyActivation energy is the minimum energy needed to start a reaction, shown as the gap from the reactants up to the top of the curve.
5
Multiple choice · Easy
Which everyday device uses an endothermic reaction?
- A sports injury cold pack
- A hand warmer that gives out heat
- A self-heating coffee can
- A burning candle
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WhySome sports injury cold packs use an endothermic reaction that takes in heat, making the pack feel cold.
6
Fill in the blank · Easy
A reaction that transfers energy to the surroundings and raises their temperature is described as .
Answer:
exothermic
WhyReactions that release energy to the surroundings are exothermic.
7
Multiple choice · Medium
For an exothermic reaction shown on a reaction profile, the products are:
- At a lower energy level than the reactants
- At a higher energy level than the reactants
- At the same energy level as the reactants
- At the same level as the top of the curve
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WhyIn an exothermic reaction the products have less stored energy than the reactants, so the product line is lower.
8
Multiple choice · Medium
During a reaction, what process requires energy to be supplied?
- Breaking bonds in the reactants
- Making bonds in the products
- Cooling the reactants
- Mixing the reactants together
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WhyBreaking chemical bonds in the reactants is an endothermic step that requires energy to be put in.
9
Multiple choice · Medium
A reaction releases energy overall. This means that:
- More energy is released making bonds than is used breaking bonds
- More energy is used breaking bonds than is released making bonds
- No bonds are broken during the reaction
- Bond breaking and bond making release equal energy
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WhyIf a reaction is exothermic overall, the energy released by making new bonds is greater than the energy needed to break the original bonds.
10
Multiple choice · Medium
How does adding a catalyst change a reaction profile?
- It lowers the activation energy
- It lowers the energy of the products only
- It raises the activation energy
- It changes the overall energy released
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WhyA catalyst provides an alternative pathway with a lower activation energy; it does not change the energy of the reactants or products.
Key terms in Energy changes
Energy change: The release or uptake of energy that accompanies a chemical reaction.
Exothermic reaction: A reaction that transfers energy to the surroundings, usually causing a rise in temperature.
Endothermic reaction: A reaction that takes in energy from the surroundings, usually causing a fall in temperature.
Conservation of energy: The principle that the total amount of energy stays the same during a chemical reaction.
Surroundings: Everything outside the reacting chemicals that can gain or lose energy during a reaction.
System: The reacting chemicals being studied, considered separately from the surroundings.
Temperature change: The rise or fall in temperature measured to show whether a reaction is exothermic or endothermic.
Thermometer: An instrument used to measure the temperature change during an energy experiment.
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