New
New
Year 10
OCR
Foundation

Breaking and making bonds

I can describe how bond making and breaking use or release energy.

New
New
Year 10
OCR
Foundation

Breaking and making bonds

I can describe how bond making and breaking use or release energy.

Lesson details

Key learning points

  1. In all chemical reactions, bonds in the reactants need to be broken before the reaction can happen
  2. Energy must be supplied to break bonds in the reactants
  3. Energy is released when bonds in the products are formed
  4. 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.

Use good examples of reactions and explain how the energy is provided to break the bonds and released making the bonds. Combustion is a good example as you provide energy to light the fuel and then energy is released as the reaction takes place.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
What does an energy profile diagram show?
Correct answer: the energy changes during a chemical reaction
the mass changes during a reaction
the temperature changes during a reaction
Q2.
What occurs during a chemical reaction?
The state of matter is changed.
Substances are mixed without a reaction.
Correct answer: Atoms are rearranged and chemical bonds are broken/formed.
Q3.
What is an exothermic reaction?
Correct answer: 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
Q4.
What is an endothermic reaction?
Correct answer: 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
Q5.
What is activation energy?
the energy released during a reaction
the energy stored in reactants
Correct answer: the minimum energy that the particles must have in order to react
Q6.
In which energy profile, does the blue arrow show the energy change of a exothermic reaction?
Correct answer: energy profile A
energy profile B
energy profile C

6 Questions

Q1.
The overall energy change for an exothermic reaction is...
Correct answer: 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.
Q2.
Photosynthesis absorbs 250 kJ of energy from the surroundings. Is this reaction endothermic or exothermic?
Correct answer: endothermic, because energy is absorbed
exothermic, because energy is released
neither, because no energy change occurs
Q3.
Given the following data: reactants energy = 200 kJ, products energy = 300 kJ, what is the overall energy change? Is the reaction endothermic or exothermic?
Correct answer: +100 kJ
100 kJ
Correct answer: endothermic reaction
exothermic reaction
Q4.
The decomposition of calcium carbonate requires 150 kJ of energy. What type of reaction is this?
Correct answer: endothermic, because energy is absorbed
exothermic, because energy is released
neutral, because no energy change occurs
Q5.
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
Correct answer: -150 kJ
endothermic reaction
Correct answer: exothermic reaction
Q6.
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
Correct answer: -200 kJ, indicating an exothermic reaction