AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Energy is conserved in chemical reactions so can therefore be neither…
Full specification wording
Key ideas: energy is conserved in chemical reactions so can therefore be neither created or destroyed.
In every chemical reaction, energy is conserved: it is neither created nor destroyed, only transferred.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 20 of 26
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In every chemical reaction, energy is conserved: it is neither created nor destroyed, only transferred. The total energy of the reactants equals the total energy of the products plus any energy transferred to or from the surroundings. In an exothermic reaction, such as burning methane, energy is transferred from the chemical store to the surroundings, causing them to warm up. In an endothermic reaction, such as thermal decomposition, energy is transferred from the surroundings to the chemical store, causing them to cool down.
What earns the marks
- States that energy is conserved in chemical reactions, meaning it is neither created nor destroyed.
- Explains that the total energy of the reactants equals the total energy of the products plus energy transferred to or from the surroundings.
- Describes an exothermic reaction as one where energy is transferred to the surroundings, raising the temperature.
- Describes an endothermic reaction as one where energy is taken in from the surroundings, lowering the temperature.
- Interprets reaction profiles to compare the relative energies of reactants and products.
Common mistakes and how to put them right
Saying that energy is 'used up' in a reaction.
Put it right: Energy is transferred between stores, not used up or destroyed.
Confusing exothermic and endothermic reactions.
Put it right: Exothermic transfers energy to the surroundings (temperature rises), while endothermic takes energy in (temperature falls).
Believing that a temperature drop means energy is lost.
Put it right: Energy is conserved, but it has been transferred from the thermal store of the surroundings to the chemical store of the products.
Exam tips
- State clearly whether energy is transferred to or from the surroundings when identifying a reaction as exothermic or endothermic.
- On a reaction profile, label the reactants, products, and overall energy change, showing activation energy as the peak.
Try the lesson
The start of the Key ideas: energy is conserved in chemical reactions so can therefore be neither created or destroyed. lesson, made from checked teaching notes for this specification point.
Have a go first
In a chemical reaction, energy is transferred between the reacting substances and their surroundings. Which statement describes what happens to the total energy of the reacting substances and the surroundings combined?
Listen
In every chemical reaction, energy is conserved: it is neither created nor destroyed, only transferred. The total energy of the reactants equals the total energy of the products plus any energy transferred to or from the surroundings. In an exothermic reaction, such as burning methane, energy is transferred from the chemical store to the surroundings, causing them to warm up. In an endothermic reaction, such as thermal decomposition, energy is transferred from the surroundings to the chemical store, causing them to cool down. A strong answer earns marks for these points. States that energy is conserved in chemical reactions, meaning it is neither created nor destroyed. Explains that the total energy of the reactants equals the total energy of the products plus energy transferred to or from the surroundings. Describes an exothermic reaction as one where energy is transferred to the surroundings, raising the temperature. Describes an endothermic reaction as one where energy is taken in from the surroundings, lowering the temperature. A common slip: Saying that energy is 'used up' in a reaction. Instead, energy is transferred between stores, not used up or destroyed. Exam tip: State clearly whether energy is transferred to or from the surroundings when identifying a reaction as exothermic or endothermic.
See it
Key words
Say what each word means before you turn the card.
Conservation of energy
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Exothermic and endothermic reactions
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Reaction profiles
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Temperature changes
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See every definition
- Conservation of energy
- Energy is conserved in chemical reactions, so it can therefore be neither created nor destroyed.
- Exothermic and endothermic reactions
- In an exothermic reaction energy is transferred to the surroundings, causing them to warm up, while in an endothermic reaction energy is transferred from the surroundings, causing them to cool down.
- Reaction profiles
- These are used to show the relative energies of reactants and products.
- Temperature changes
- These show whether energy is transferred to the surroundings, raising the temperature, or taken in from the surroundings, lowering the temperature.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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