Chemistry- Energy changes and reversible reactions

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What always takes place at a chemical reaction?
An energy change
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What two types of reactions are there?
Exothermic and endothermic
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What happens during an exothermic reaction?
Energy given out, temperature rises, new bonds are formed
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What happens during an endothermic reaction?
Energy taken in, temperature falls, bonds are broken
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What are the examples of an exothermic reaction?
Respiration, combustion of fuels, neutralisation
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What are the examples of an endothermic reaction?
Cooking, photosynthesis
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What is energy measured in?
Kilojoules
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What takes in energy?
Breaking bonds
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What gives out energy?
Making bonds
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When is a reaction exothermic?
When the energy needed to break bonds is less than the energy released by creating bonds
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When is a reaction endothermic?
When the energy needed to break bonds is greater than the energy released by creating bonds
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What is bond energy?
The energy released when bonds are formed or taken in when they are broken
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How to calculate energy change?
Energy in - energy out =
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What is a fuel?
Any substance we use to provide energy
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Which fuels do we burn?
Fossil fuels
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Name the fossil fuels
Coal, natural gas, petroleum
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What two fuels are of growing importance?
Ethanol and hydrogen
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What is ethanol?
Alcohol, C2H5OH
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How can ethanol be made?
From any plant material
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Where is ethanol used?
In car engines
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What is hydrogen?
A gas that explosively burns in oxygen
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Where is hydrogen used?
As rocket fuel, hydrogen fuel cells
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Which fuels do we not burn and why?
Nuclear fuel. They contain radioactive isotopes that decay on their own.
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How can you force a radioactive isotope to decay?
By shooting neutrons at it
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Which radioisotope do we commonly use?
Uranium- 235
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What are the advantages of nuclear fuels?
They give out plenty of energy and they don't form pollutants
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What are the disadvantages of nuclear fuels?
They are very dangerous
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How are simple cells and electrolysis different?
Simple cells use the reaction to generate a current and electrolysis uses the current to bring about the reaction
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What happens in a hydrogen fuel cell?
A redox reaction where hydrogen reacts with oxygen to form water
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Where is hydrogen and where is oxygen in a hydrogen fuel cell?
Hydrogen at the negative pole and oxygen at the positive pole
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What are the advantages of a hydrogen fuel cell?
Only water is formed, plenty of energy we won't run out of hydrogen
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What is a reversible reaction?
A reaction that can goes forward and back
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What are the two chemical tests for water?
White anhydrous copper sulphate turns blue and blue cobalt chloride paper turns pink
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What does hydrated mean?
It has water molecules built into its structure
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What amount of energy transferred both ways in a reversible reaction?
Same amount
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Are reversible reactions endothermic? Exothermic?
They are exothermic in one way and endothermic the other way
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Are many important reactions reversible?
Yes
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What are the uses of ammonia?
Nitric acid and fertilisers
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What does equilibrium mean?
No overall change because forward and back reactions take place at the same rate
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Why are reversible reactions a challenge for industry?
Because they are never complete
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How to create new equilibrium?
Make a change to the reaction that is already in equilibrium
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How can you shift equilibrium?
By changing pressure, by removing the yield, by adding a catalyst
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How does changing the pressure shift the equilibrium?
The system will act to oppose the change by forming the product so that there are fewer molecules
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How does removing the yield shift the equilibrium?
Cool the mixture to allow the product to condense, remove it, and then heat the mixture again to make more
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How does adding a catalysts shift the equilibrium?
It will just speed up both reactions so equilibrium will be reached faster but the yield will stay the same
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How does increasing the concentration shift equilibrium?
It increases the yield
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Other cards in this set

Card 2

Front

What two types of reactions are there?

Back

Exothermic and endothermic

Card 3

Front

What happens during an exothermic reaction?

Back

Preview of the front of card 3

Card 4

Front

What happens during an endothermic reaction?

Back

Preview of the front of card 4

Card 5

Front

What are the examples of an exothermic reaction?

Back

Preview of the front of card 5
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