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Chem 4: Ozone Story > OZ5: Ozone > Flashcards

OZ5: Ozone Flashcards

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1
Q

Define homogeneous catalysis.

A
  • Catalysis where the reactants and catalysts have the same physical state
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2
Q

How does homogeneous catalysis work?

A
  • Intermediate compounds are formed

- These break down to form products and reform catalysts

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3
Q

What does the enthalpy profile for homogeneous catalysis look like?

A
  • Two humps for each step (first=intermediate compounds formed, second=intermediate compounds breaking down)
  • Combined activation enthalpy is lower than the same reaction without a catalyst
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4
Q

Where does photodissociation occur?

A

Stratosphere

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5
Q

What type of compound undergoes photodissociation to form radicals which contribute to the breakdown of ozone?

A

Haloalkanes e.g CH3Cl/CH3Br

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6
Q

What occurs in the photodissociation of haloalkanes?

A
  • High energy UV radiation is absorbed by the haloalkane

- This breaks the C-halogen bond homolytically to form 2 free radicals

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7
Q

What is the photodissociation of haloalkanes an example of?

A

Initiation

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8
Q

What does the ease of the photodissociation of haloalkanes depend on?

A

The carbon-halogen bond enthalpy

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9
Q

Why is the carbon-iodine bond more likely to break than the carbon-chlorine bond?

A

C-I has a lower bond enthalpy

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10
Q

Why are only a few haloalkanes broken down by UV in the troposphere?

A

Most of the high frequency UV has been absorbed by the ozone layer

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11
Q

Why are halogen radicals (e.g Cl.) bad for the atmosphere?

A

They are catalysts for the breakdown of ozone

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12
Q

Give the two steps in the homogenous catalysis of the breakdown of ozone by chlorine radicals.

A
  1. Cl.+ O3 ===> ClO. + O2

2. ClO. + O ===> Cl. + O2

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13
Q

What is the intermediate compound formed in the homogenous catalysis of the breakdown of ozone by chlorine radicals?

A

ClO. (Chlorine monoxide)

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14
Q

What is the overall reaction for the breakdown of ozone?

A

O3 + O ====> 2O2

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15
Q

Give the two steps in the homogenous catalysis of the breakdown of ozone by hydroxyl radicals.

A
  1. HO. + O3 ====> HO2 + O2

2. HO2 + O ====> HO + O2

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16
Q

What is the homogenous catalysis of the breakdown of ozone by chlorine radicals an example of?

A

Propagation

17
Q

Why is homogenous catalysis of the breakdown of ozone by chlorine radicals particularly dangerous, despite there being a low concentration of Cl radicals?

A
  • The reaction happens 1500 times faster than ozone can be reformed
  • Chlorine radicals are regenerated and can go on to degenerate more ozone
18
Q

How is ozone formed?

A

By UV radiation from the sun hitting oxygen molecules

19
Q

Where is ozone formed?

A

Stratosphere

20
Q

Give the two equations for the formation of ozone.

A
  1. O2 + hv ====> O + O

2. O2 + O ====> O3

21
Q

Give the equation for UV radiation reversing the formation of ozone.

A

O3 + hv ====> O2 + O

22
Q

How is an equilibrium set up between the formation of ozone and its breakdown?

A

The ozone layer is constantly being replaced or destroyed by UV radiation either hitting ozone or oxygen molecules

23
Q

Give the equation for the reversible reaction for ozone formation and destruction.

A

O2 + O O3

24
Q

Why is ozone important?

A

It absorbs high energy UV radiation when it breaks down

25
Q

What problems does ozone cause?

A
  • Ages skin
  • Mutates DNA in skin cells causing skin cancer
  • Damages eyes
  • Damages crops
26
Q

Why is UV radiation still essential to humans?

A

Helps humans produce vitamin D

27
Q

How is ozone formed in the troposphere?

A

Nitrogen dioxide and hydrocarbons from vehicle engines and power stations react in the sunlight to form ozone

28
Q

How is photochemical smog formed?

A

Ozone and carbon particulates mixing

29
Q

Why is photochemical smog harmful? (3)

A
  • Haziness and reduced visibility in the air
  • Respiratory problems
  • Eye irritation
30
Q

Give the two steps in the homogenous catalysis of the breakdown of ozone by nitrogen monoxide radicals

A
  1. NO + O3 ====> NO2 + O2

2. NO2 + O ===> NO + O2

Chem 4: Ozone Story (7 decks)

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