C3 Chapter 3 Energy of reactions

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How is energy transferred in an exothermic reaction? Give an example.
Energy is released. eg/ combustion
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How do we know that it is an exothermic reaction?
The temperature of the surroundings increase.
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How is energy transferred in an endothermic reaction? Give an example.
Energy is taken in. eg/ thermal decompostion, photosynthesis
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What is activation energy?
The energy needed for the reaction to take place.
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What do energy level diagrams do?
Shows energy-reactants+products. Whether its endo/exo
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On an energy level diagram, how do we know what the activation energy is?
Top of curve, difference of reactants and top of curve
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How do we know what the energy taken in or released is?
The difference between the reactants and the products
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HOW do catalysts increase the rate of reaction?
A different pathway. Lowers activation energy needed.
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How do we find the energy released from burning fuels? (equation)
Q=mcΔT= mass x SHC x rise in temp. (water)
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What is normally the SHC of water?
4.2J/g/oC
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How do we find the energy released per gram of fuel?
Divide by amount of fuel burned
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Why is a calorimeter used?
Metal is conductive => Heat passes into water easier
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Why should we stir the water?
For even heat distribution.
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Why is the energy measured always less than the energy of the fuel?
A lot of heat escapes into surroundings rather than the water
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What do we get if we react lithium with water?
Lithium hydroxide+hydrogen
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Why is a polystyrene cup used?
Reduces heat escaping-Insulator-More accurate results
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What is the vital part of the experiment?
Measure start temp. and end temp. of water for difference.
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What do we get if we react sodium hydroxide with hydrochloric acid?
Sodium chloride and water
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How can we improve the experiment?
Use a lid, stir the reaction for even heat distribution
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In an exothermic reaction, are energy changes shown to be positive or negative?
Negative. Energy transferred to other chemicals
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In an endothermic reaction, are energy changes shown to be positive or negative?
Positive. Energy is gained.
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Does breaking bonds require energy or does it release energy?
Requires energy (endo)
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Does making bonds require energy or does it release energy?
Releases energy (exo)
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How do the reactants react to make a new compound in terms of bond energies?
The bonds are broken, bonds are made for the new product/s
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How do we find out whether it's an exothermic/endothermic reaction?
"Bond breaking energy" minus the "bond making energy"
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How can hydrogen be used as a fuel to power vehicles?
Burn in a combustion engine or use in a fuel cell.
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What is the hydrogen burnt in to use as a fuel for cars?
Oxygen
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Is the reaction exo/endothemic between hydrogen and oxygen?
exothermic. releases energy when reacted
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What type of energy is produced from hydrogen?
Electrical
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What are the advantages of burning H2 in vehicles?
Combines with oxygen in the air; forms just WATER. Very clean
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What are the disadvantages with burning H2 in vehicles?
Expensive engine, energy from other source needed, explosive
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What does a fuel cell need?
Fuel+oxygen
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How does it gain energy and make electricity?
Uses the energy from the reaction to generate electricity.
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How do we carry out the experiment?
Calorimeter, water temp., spirit temp., stir, flame out, temps.
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Other cards in this set

Card 2

Front

How do we know that it is an exothermic reaction?

Back

The temperature of the surroundings increase.

Card 3

Front

How is energy transferred in an endothermic reaction? Give an example.

Back

Preview of the front of card 3

Card 4

Front

What is activation energy?

Back

Preview of the front of card 4

Card 5

Front

What do energy level diagrams do?

Back

Preview of the front of card 5
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