Energy changes in chemical reactions

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What are exothermic reactions?
Reactions that transfer energy to the surroundings and heats up its surroundings
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Give three examples of exothermic reactions:
Combustion, oxidation reactions, neutralisation reactions
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What enthalpy change do exothermic reactions have?
A negative one
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What are endothermic reactions?
Reactions that take in energy from the surroundings, therefore causing a decrease in temperature
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What enthalpy change do endothermic reactions have?
A positive one
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Why do thermal decomposition reactions have to be heated continuously?
To keep the reaction going
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Why do simple calorimeters not give accurate results for the energy realeased?
Because much of the energy heats the surroundings
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How can we reduce the energy transfers to the surrundings?
By doing reactions in an insulated container - like a polystyrene cup
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What happens to bonds in endothermic reactions?
They are broken
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Why does bond breaking cause an endothermic reaction?
Because the bond breaking requires more energy than the energy released when new bonds are formed
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What happens to bonds in exothermic reactions?
They are formed
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Why does bond formation cause an exothermic reaction?
Because bond forming releases energy which is greater than the energy used in breaking old bonds
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What is the activation energy?
The minimum energy needed for a reaction to happen
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How do catalysts increase the rate of reaction?
They provide a different pathway with an activation energy that is lower
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Card 2

Front

Give three examples of exothermic reactions:

Back

Combustion, oxidation reactions, neutralisation reactions

Card 3

Front

What enthalpy change do exothermic reactions have?

Back

Preview of the front of card 3

Card 4

Front

What are endothermic reactions?

Back

Preview of the front of card 4

Card 5

Front

What enthalpy change do endothermic reactions have?

Back

Preview of the front of card 5
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