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chemistry > Energy changes > Flashcards

Energy changes Flashcards

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1
Q

What is an exothermic change?

A

change where heat is given out to the surroundings

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2
Q

What are some examples of exothermic changes? [7]

A 
condensation
freezing
dissolving of acids
combustion
respiration
neutralisation
corrosion / rusting
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3
Q

What is an endothermic change?

A

change where heat is absorbed from the surroundings

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4
Q

What are some examples of endothermic changes? [4]

A

evaporation
melting
photosynthesis
thermal decomposition

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5
Q

What is enthalpy change (ΔH) ?

A

represents the difference in energy content of the reactants and products

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6
Q

How to calculate enthalpy change?

A

bond breaking - bond making

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7
Q

Is the enthalpy change for exothermic reactions positive or negative?

A

negative

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8
Q

Is the enthalpy change for endothermic reactions positive or negative?

A

positive

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9
Q

How to tell if a reaction is exothermic?

A

the energy released for bond making is greater than the energy absorbed for bond breaking

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10
Q

How to tell if reaction is endothermic?

A

the energy released for bond breaking is less than the energy absorbed for bond making

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11
Q

How to draw enthalpy change on energy level / profile diagram?

A

reactant to product

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12
Q

What is activation energy?

A

minimum amount of energy that reactant particles must possess in order for a chemical reaction to occur

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13
Q

How to draw activation energy in energy profile diagram?

A

reactant to highest point

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14
Q

What are fuels?

A

substances that can burn in air to give out heat energy

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15
Q

What happens at the positive electrode in a hydrogen-oxygen fuel cell?

A

oxygen is reduced to form hydroxide ions

O2(g) + 2H2O(l) + 4e- —> 4OH- (aq)

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16
Q

What happens at the negative electrode of a hydrogen-oxygen fuel cell?

A

hydrogen is oxidised to form water

2H2(g) + 4OH- (aq) —> 4H2O(l) + 4e-

17
Q

What is the overall reaction for a hydrogen-oxygen fuel cell?

A

2H2(g) + O2(g) —> 2H2O(l)

18
Q

What are the advantages of using hydrogen as fuel? [3]

A

does not cause pollution
renewable source of energy
efficient source of energy

19
Q

What are the disadvantages of using hydrogen as a fuel? [3]

A

no cheap sources of hydrogen
extremely flammable and explosive
very light

chemistry (5 decks)

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