Starter quiz
- What does an energy profile diagram show?
- the energy changes during a chemical reaction ✓
- the mass changes during a reaction
- the temperature changes during a reaction
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- What occurs during a chemical reaction?
- The state of matter is changed.
- Substances are mixed without a reaction.
- Atoms are rearranged and chemical bonds are broken/formed. ✓
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- What is an exothermic reaction?
- a reaction where energy is transferred from the reactants to the surrounding ✓
- a reaction that absorbs energy from the surroundings
- a reaction that does not involve energy change
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- What is an endothermic reaction?
- a reaction in which energy is transferred from the surroundings to the products ✓
- a reaction that does not involve energy change
- a reaction that releases energy to the surroundings
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- What is activation energy?
- the energy released during a reaction
- the energy stored in reactants
- the minimum energy that the particles must have in order to react ✓
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- In which energy profile does the blue arrow show the energy change of an exothermic reaction?
energy profile A
energy profile B
energy profile C
Exit quiz
- The overall energy change for an exothermic reaction is...
- negative, because the energy released is greater than the energy absorbed. ✓
- positive, because the energy absorbed is greater than the energy released.
- zero, because no energy change occurs.
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- Given the following data: reactants energy = 200 kJ, products energy = 300 kJ, what is the overall energy change? Is the reaction endothermic or exothermic?
- +100 kJ ✓
- -100 kJ
- endothermic reaction ✓
- exothermic reaction
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- Given the following data: reactants energy = 400 kJ, products energy = 250 kJ, what is the overall energy change? Is the reaction endothermic or exothermic?
- +150 kJ
- -150 kJ ✓
- endothermic reaction
- exothermic reaction ✓
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- During the combustion of methane, the reactants have an energy of 500 kJ and the products have an energy of 300 kJ. What is the overall energy change? Is the reaction endothermic or exothermic?
- +200 kJ, indicating an endothermic reaction
- -200 kJ, indicating an endothermic reaction
- +200 kJ, indicating an exothermic reaction
- -200 kJ, indicating an exothermic reaction ✓
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How many C-H bonds are there in the reactants and in the products of this reaction?- 6 C-H bonds in the reactants
- 5 C-H bonds in the reactants ✓
- 6 C-H bonds in the products
- 4 C-H bonds in the products ✓
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What is the overall energy change when ethanol (C₂H₅OH) reacts to form ethene (C₂H₄) and water (H₂O)? Give your answer in kJ/mol.- '+45 kJ/mol' ✓
Worksheet
Presentation
Video
Lesson Details
Key learning points
- The energy needed to break bonds and the energy released when bonds are formed can be calculated from bond energies.
- The difference between the energy needed to break bonds and the energy released is the overall energy change.
Common misconception
Pupils often make mistakes when identifying the different types of bonds and the number of each in a molecule. They may also reverse the calculation of the overall energy change, as make - break.
Molecules can be complex and should be drawn to show all the bonds. Emphasis that double and triple covalent bonds are different to single bonds. Pupils should be instructed to consider whether a reaction is exothermic or endothermic.
Keywords
Endothermic - An endothermic chemical reaction is a type of reaction in which energy is transferred from the surroundings to the products, e.g. photosynthesis.
Exothermic - An exothermic chemical reaction is a type of reaction in which energy is transferred from the reactants to the surroundings, e.g. combustion.
Activation energy - The minimum energy that the particles must have in order to react is known as the activation energy.
Bond energy - The energy required to break a covalent bond, or released when making a covalent bond. is known as the bond energy.