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 a 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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- Photosynthesis absorbs 250 kJ of energy from the surroundings. Is this reaction endothermic or exothermic?
- endothermic, because energy is absorbed ✓
- exothermic, because energy is released
- neither, 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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- The decomposition of calcium carbonate requires 150 kJ of energy. What type of reaction is this?
- endothermic, because energy is absorbed ✓
- exothermic, because energy is released
- neutral, because no energy change occurs
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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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Worksheet
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Video
Lesson Details
Key learning points
- In all chemical reactions, bonds in the reactants need to be broken before the reaction can happen
- Energy must be supplied to break bonds in the reactants
- Energy is released when bonds in the products are formed
- The difference between the energy needed to break bonds and the energy released is the overall energy change
Common misconception
Pupils often confuse the ideas that bonds require energy to break i.e. endothermic process and that energy is released forming bonds i.e. exothermic process.
Bonds will not break unless energy is absorbed to do so. The formation of a bond releases energy to the surroundings.
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.
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