chemistry - unit 5 - energy changes
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22 Terms
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The 2 or more substances that react together in a reaction
Reactants
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The substance/s made in a reaction
Products
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A reaction where heat energy is made and given off to the surroundings so the temperature rises
Exothermic reaction
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A reaction where heat energy is taken in from the surroundings so the temperature decreases
Endothermic reaction
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Energy needed to start a reaction
Activation energy
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A graph which tells us the energy of reactants and products as reaction occurs with energy on the Y axis and time on the X axis
Reaction Profile
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The amount of energy that will either break a bond between atoms or create a bond
Bond energy
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Here the activation energy is less than that used to form bond and so energy is lost to the surrounding and the energy change is negative
Draw a reaction profile for an exothermic reaction
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Here the activation energy is larger than that used to form bonds and so energy is gained from the surrounding and there is a positive energy change
Draw a reaction profile for an endothermic reaction
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A chemical change
What type of reaction is a temperature change associated with?
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Endothermic - as heat energy is taken in
What type of process is bond breaking?
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Exothermic - as heat energy is given out when bonds are made
What type of process is bond making?
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Contributes to global warming as hydrogen has to be heated to break bonds
Disadvantages of non-rechargeable batteries?
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example of endothermic
Cold pack for injuries
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example of exothermic
Combustion
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bonds breaking
endothermic
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bonds forming
exothermic
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During a chemical reaction
Bonds are both broken and formed
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The greater the activation energy
The more energy is needed to start the reaction
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What happens in exothermic reactions?
More energy is released by making bonds than used to break them
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What happens in endothermic reactions?
The energy used to break the bonds is greater than the energy released by making bonds
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How are bond energies calculated?
1. Find energy used to Break bonds
2. Find energy released by Forming bonds
3. Take 'Formed' away from 'Broken'
Note 
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