C5 energy changes Flashcards

1
Q

what is the conservation of energy rule

A

Energy is not created or destroyed, only transferred. The total amount of energy in the universe stays the same.

if a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants by the amount transferred

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2
Q

what is an exothermic reaction

A

a reaction that transfers energy to the surroundings

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3
Q

name 2 features of exothermic reactions

Give two examples

A

-temperature of surroundings increases
-product molecules must have less energy than the reactants by the amount transferred

Combustion, neutralisation reaction.

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4
Q

what’s an endothermic reaction

A

a reaction that takes in energy from the surroundings so the temperature of the surroundings decreases

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5
Q

what are 2 features of an endothermic reaction

Give an example of a use of an endothermic reaction.

A

-temperature of surroundings decreases
-product molecules must have more energy than reactants

For example sports injury packs.

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6
Q

what is activation energy

A

minimum amount of energy that particles that need to have to react

Difference in energy between the energy of the reactants and the highest point in the reaction profile.

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7
Q

why must energy be supplied in reactions

A

to break down the bonds of the reactants

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8
Q

how do you calculate overall energy change

A

sum of energy taken in to break bonds - sum of energy released to form bonds

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9
Q

what are cells

A

they contain chemicals which react to produce electricity

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10
Q

how can a simple cell be made

A

connecting two different metals in contact with an electrolyte

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11
Q

what is a battery

A

two or more cells together to grant a greater voltage

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12
Q

explain non rechargeable batteries

A

-chemical reactions stop when one of the reactants has been used up
-alkaline batteries are always non-rechargeable

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13
Q

explain rechargeable batteries

A

chemical reactions are reversed when an external electrical current is supplied

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14
Q

what are some advantages of hydrogen fuel cells

what about disadvantages?

A

Advantages:
-can be used constantly provided fuel is supplied.
-only produces water when burnt (no greenhouse gas emissions)

Disadvantages:
-hydrogen gas needs to be stored at high pressure and is difficult to transport

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15
Q

What are some advantages of rechargeable cells/batteries?

What about disadvantages?

A

Advantages:
-Can be recharged using electricity so fuel does not have to be supplied.

Disadvantages:
-Hard to dispose of (non-biodegradeable)
-Will eventually stop working

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16
Q

what is the half equation for a hydrogen fuel cell at the cathode

A

H2(g) -> 2e- + 2H+(aq)

17
Q

what is the half equation for a hydrogen fuel cell at the anode

A

4H+(aq) + O2(g) + 4e- -> 2H2O(g)=