GCSE ChemistryAQA, Edexcel and OCR
20 chemistry questions on energy changes. Pick your answer, then tap to see if you were right and why. Every answer comes from the Show Working science bank, checked against the GCSE content every board in England teaches.
01 / Quiz yourselfTry it, then tap to check
Choose your answer before you open it. Then read why, so it sticks.
01 / Energy changesBoth tiers
Answer: B It rises
An exothermic reaction transfers energy to the surroundings, so the temperature of the surroundings goes up. A thermometer in the reaction mixture shows a rise.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.1 Energy transfer during exothermic and endothermic reactions
02 / Energy changesBoth tiers
Answer: A It falls
An endothermic reaction takes in energy from the surroundings, so the temperature of the surroundings goes down. The reaction mixture feels cold.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.1 Energy transfer during exothermic and endothermic reactions
03 / Energy changesBoth tiers
Answer: C Burning methane
Combustion, neutralisation and many oxidation reactions, such as respiration and rusting, are exothermic. They give out energy to the surroundings.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.1 Energy transfer during exothermic and endothermic reactions
04 / Energy changesBoth tiers
Answer: A Thermal decomposition
Thermal decompositions take in energy to break a compound down. A burning candle needs a flame to start it, but once going it gives out much more energy than it took in, so it is exothermic.
Checked against OCR Gateway Chemistry A J248 specification, C3.2 Energetics
05 / Energy changesBoth tiers
Answer: B It is transferred, never created or destroyed
Energy is conserved in reactions. If a reaction transfers energy to the surroundings, the products must store less energy than the reactants. In an endothermic reaction the products store more.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.1 Energy transfer during exothermic and endothermic reactions
06 / Energy changesBoth tiers
Answer: B Measure the temperature and see it rise
Reactions in solution, such as neutralisation, displacement and precipitation, and salts dissolving, all come with energy changes. Measuring the temperature before and after shows whether energy was given out or taken in.
Checked against Pearson Edexcel GCSE Chemistry 1CH0 specification, 7.9 Rates of reaction and energy changes
07 / Energy changesBoth tiers
Answer: D Lower in energy than the reactants
A reaction profile plots energy against the progress of the reaction. In an exothermic reaction the products end lower than the reactants, as energy was given out. In an endothermic reaction they end higher.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.2 Reaction profiles
08 / Energy changesBoth tiers
Answer: B From the reactants up to the top of the curve
The activation energy is drawn from the reactants' energy up to the peak of the curve. The difference between the reactants' and products' energy is the overall energy change of the reaction.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.2 Reaction profiles
09 / Energy changesBoth tiers
Answer: B The minimum energy particles need to react when they collide
Reacting particles must collide with at least a minimum amount of energy, the activation energy, to react. A match supplies this to start a fire; after that the energy given out keeps the reaction going.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.2 Reaction profiles
10 / Energy changesHigher only
Answer: B Endothermic: energy is taken in
Energy must be supplied to break bonds, so bond breaking is endothermic. Energy is released when new bonds form, so bond making is exothermic. A common mistake is to think that breaking bonds releases energy.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.3 The energy changes of reactions
11 / Energy changesHigher only
Answer: D Making bonds releases more energy than breaking bonds takes in
Overall energy change = energy taken in to break bonds − energy released making bonds. If more energy is released making bonds than is taken in breaking them, the answer is negative and the reaction is exothermic. If it is positive, it is endothermic.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.1.3 The energy changes of reactions
12 / Energy changesBoth tiers
Answer: A A compound of hydrogen and carbon only
Hydrocarbons are compounds made of hydrogen and carbon atoms only. Crude oil is the main source of them: most of the compounds in it are hydrocarbons.
Checked against AQA GCSE Chemistry 8462 specification, 4.7.1.1 Crude oil, hydrocarbons and alkanes
13 / Energy changesBoth tiers
Answer: A A mixture of many compounds, mostly hydrocarbons
Crude oil is a mixture of a huge number of compounds, mostly hydrocarbons. Its fractions are used as fuels and as feedstock: the raw material the petrochemical industry uses to make polymers, solvents, lubricants and detergents.
Checked against AQA GCSE Chemistry 8462 specification, 4.7.1.2 Fractional distillation and petrochemicals
14 / Energy changesBoth tiers
Answer: A Its supply is limited and will run out
Crude oil took millions of years to form, far more slowly than we use it. There is a limited amount, so it is finite: once used up, it cannot be replaced in a human lifetime.
Checked against AQA GCSE Chemistry 8462 specification, 4.7.1.1 Crude oil, hydrocarbons and alkanes
15 / Energy changesBoth tiers
Answer: C Plastic bags
Modern life depends on crude oil. It gives fuels such as petrol, diesel, kerosene and liquefied petroleum gases, and the petrochemical industry turns it into plastics, solvents, lubricants and detergents.
Checked against AQA GCSE Chemistry 8462 specification, 4.7.1.2 Fractional distillation and petrochemicals
16 / Energy changesBoth tiers
Answer: B They give most transport fuels and the raw materials for plastics
Cars, lorries, ships and planes mostly run on fuels from crude oil, and much heating and electricity uses hydrocarbons too. Most plastics and many other everyday materials are made from them.
Checked against Pearson Edexcel GCSE Chemistry 1CH0 specification, 8.15 Fuels and Earth science
17 / Energy changesBoth tiers · separate only
Answer: B Until one of the reactants is used up
A chemical cell contains chemicals that react to produce a potential difference. In a non-rechargeable cell, such as an alkaline battery, the reactions stop when one reactant is used up.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.2.1 Cells and batteries
18 / Energy changesBoth tiers · separate only
Answer: A Water
In a hydrogen fuel cell, hydrogen and oxygen are supplied from outside. The hydrogen is oxidised to produce a potential difference, and the only product is water.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.2.2 Fuel cells
19 / Energy changesBoth tiers · separate only
Answer: C It keeps working as long as fuel is supplied
A fuel cell is fed with fuel and oxygen from outside, so it does not need recharging, only refuelling. Hydrogen fuel cells produce only water, while batteries contain chemicals that are harder to dispose of and can only be recharged so many times.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.2.2 Fuel cells
20 / Energy changesBoth tiers · separate only
Answer: B Hydrogen is a flammable gas that is hard to store
Hydrogen is a flammable gas that takes up a lot of space, so it must be stored under high pressure. Much hydrogen is made from fossil fuels or with electricity from them, so fuel cells are not always as clean as they look.
Checked against AQA GCSE Chemistry 8462 specification, 4.5.2.2 Fuel cells
02 / Longer answersMarked by levels
Write your answer first, on paper. Then open it and tick off the points you made. How 6-mark questions are marked.
6 marks / Why burning methane releases energyHigher only
Methane burns completely in oxygen: CH₄ + 2O₂ → CO₂ + 2H₂O.
In any reaction, existing bonds in the reactants must be broken and new bonds in the products are made. Breaking a bond needs energy to be supplied, so bond breaking is endothermic. Making a bond releases energy, so bond making is exothermic. When methane burns, the four C–H bonds in each methane molecule and the O=O double bonds in the two oxygen molecules are broken, which takes in energy. Then new bonds form: two C=O double bonds in the carbon dioxide molecule and four O–H bonds in the two water molecules, which releases energy. For methane combustion, the energy released when these new bonds are made is greater than the energy needed to break the bonds in the reactants. The difference is transferred to the surroundings as heat, so the temperature of the surroundings goes up and the reaction is exothermic. On a reaction profile, this shows as the products being at a lower energy level than the reactants, although some energy, the activation energy, is still needed to start the reaction.
Saying energy is released when bonds break is the classic error, and so is saying both breaking and making take in energy. Breaking takes in energy; making gives it out.
6 marks / Fuel cells or batteries for carsBoth tiers · separate only
Some electric cars are powered by hydrogen fuel cells. Others use rechargeable batteries that are charged from the mains. A hydrogen car can be refuelled in a few minutes. A battery car can take several hours to charge fully.
In a hydrogen fuel cell, hydrogen is oxidised by oxygen from the air to produce a potential difference, and the only product is water. This means the car releases no carbon dioxide or polluting gases while it is driven. A fuel cell keeps producing electricity as long as hydrogen is supplied, and refilling the tank takes only a few minutes, compared with several hours to charge a battery. Batteries also wear out after a limited number of recharges, and they contain metals and chemicals that are difficult to recycle and can be toxic when they are thrown away. However, hydrogen has disadvantages too. It is a flammable gas, so it must be stored in strong tanks under high pressure, which takes up space and carries a risk of explosion. Most hydrogen is made from fossil fuels, or by electrolysis of water using electricity that may come from power stations burning fossil fuels, so carbon dioxide can still be released. There are also very few hydrogen filling stations. Overall, fuel cells are better for long journeys and quick refuelling, but until hydrogen is made cleanly and widely available, batteries are the more practical choice.
Saying fuel cells are “completely pollution free” ignores how the hydrogen is made. An evaluation must cover both sides and finish with a judgement and a reason.
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