OZ5: Ozone Flashcards

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.

24
Q

Why is ozone important?

A

It absorbs high energy UV radiation when it breaks down

25
What problems does ozone cause?
- Ages skin - Mutates DNA in skin cells causing skin cancer - Damages eyes - Damages crops
26
Why is UV radiation still essential to humans?
Helps humans produce vitamin D
27
How is ozone formed in the troposphere?
Nitrogen dioxide and hydrocarbons from vehicle engines and power stations react in the sunlight to form ozone
28
How is photochemical smog formed?
Ozone and carbon particulates mixing
29
Why is photochemical smog harmful? (3)
- Haziness and reduced visibility in the air - Respiratory problems - Eye irritation
30
Give the two steps in the homogenous catalysis of the breakdown of ozone by nitrogen monoxide radicals
1. NO + O3 ====> NO2 + O2 | 2. NO2 + O ===> NO + O2