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Chemical Energy

Revision for Year 8 Text

Are chemical changes reversible or not reversible? Not reversible.
Are physical changes reversible or not reversible? Reversible.
What is a chemical reaction? When reactions occur, the atoms change partners and new bonds form.
What energy is being used to hold the atoms together in molecules? Chemical Energy
What is an endothermic reaction? A reaction in which heat energy is “absorbed” from the surrounding air
What is an exothermic reaction? Areaction that “releases” energy in the form of heat & sometimes light into the air.
What happens to the temperature of an exothermic reaction? It increases.
What happens to the temperature of an endothermic reaction? It decreases.
Do breaking chemical bonds take in energy or give out energy? They take in energy.
Is the breaking of chemical bonds endothermic or exothermic? Endothermic.
Breaking bonds takes in or gives out energy? Takes in.
Does forming new bonds take in or give out energy? Gives out energy = exothermic.
What do catalysts do? They speed up a chemical reaction.
Are catalysts used up in a reaction? No
What is activation energy? This is the energy needed to start a chemical reaction.
How do most catalysts work? They lower the reactions activation energy. This lowers the amount of energy needed for the reaction to proceed and helps reactions occur faster.
What is a biological catalyst called? An enzyme.
Give another definition of a chemical reaction. The process of rearrangement of two or more molecules to form new substances.
Describe two advantages of using catalysts. Catalysts speed up the rate of reaction, which saves money Catalysts allow the reaction to work at a much lower temperature. This reduces the energy used up in a reaction which is good for sustainable development.
What are some disadvantages of using catalysts? They are very expensive to buy. They often need to be removed from a product and cleaned. Different reactions use different catalysts. Catalysts can be ruined by impurities, so they stop working


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