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Organic Chemistry > Chloroalkanes and CFC'S > Flashcards

Chloroalkanes and CFC'S Flashcards

1
Q

What is a free radical

A

A particle with an un unpaired electron

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2
Q

How are free radicals formed?

A

When a covalent bond splits equally, giving one electron to each atom, homolytic fission

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3
Q

What makes particles very reactive

A

unpaired electrons

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4
Q

How are free radicals identified?

A

Cl•

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5
Q

What is formed when halogens and alkanes react together?

A

Halogenoalkanes

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6
Q

What type of reactions form halogenoalkanes

A

Photochemical reactions

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7
Q

Describe a free radical substitution reaction

A

> Started by ultraviolet light
A hydrogen atom is replaced by either chlorine or bromine

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8
Q

How many stages are free radical substitution reactions grouped into? and name them

A

3
>Initiation reactions
>Propagation reactions
>Termination reactions

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9
Q

Describe each free radical substitution reaction

A

> Initiation reactions: Free radicals are produced, sunlight provides enough energy to break Cl-Cl bond, Photodissociation
Cl2-> (UV) 2Cl

> Propagation reactions: Free radicals are used up and created in a chain reaction until all the molecules are used up

> Termination Reactions: Two free radicals join together and they make a stable molecule, the two unpaired electrons form a covalent bond

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10
Q

What determines which product will be in excess in a free radical substitution reaction?

A

If there is excess of a halogen, di, tri, tetra e.g. tetrachloromethane

If there is excess of the alkane the product will be mostly e.g Chloromethane

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11
Q

What are chlorofluorocarbons?

A

Halogenoalkane molecules where all of the hydrogen atoms have been replaced by chlorine and fluorine atoms

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12
Q

What ions destroy the ozone layer and why?

A

Chlorine free radicals because they as a catalyst for forming oxygen molecules

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13
Q

What is the symbol for ozone

A

O3

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14
Q

How is ozone formed?

A
  • When an oxygen molecule is broken down into two free radicals by ultraviolet radiation. They attack other oxygen molecules forming the ozone
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15
Q

What is the function of the ozone?

A

Absorbs ultraviolet radiation from the sun because ultraviolet radiation can cause skin cancer and skin burn

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16
Q

Describe how holes are created are in the ozone and give the reaction steps.

A

> Chlorine free radicals are formed in the upper atmosphere when C-Cl bonds in CFCs are broken down by ultraviolet radiation.

> These chlorine free radicals are catalysts

> They react with ozone to form an intermediate (ClO•) and an oxygen molecule

17
Q

What was the use of CFC’s and why are CFC’s banned?

A

> Once used as coolant gas in fridges, as solvents and as propellants in aerosols

> Advantages couldn’t outweigh the environmental problems they were causing

> Alternatives of CFC’s are HFC’s (hydrofluorocarbons) and hydrocarbons

18
Q

why is ultraviolet light needed for a initiation reaction to occur

A

it provides energy to break covalent bonds in chlorine to from chlorine free radicals

19
Q

how do greenhouse gases contribute to global warming

A

Absorb infrared radiation
molecules have polar bonds

20
Q

What is the equation for how ozone is formed

A

• O2 -> (UV) O• + O•
• O2 + O• -> O3

21
Q

Explain with the aid of equations how chlorine atoms act as a catalyst in the decompositions of ozone into oxygen

A
  • Ultraviolet radiation
  • C-Cl bond breakage
  • Cl• + O3 -> ClO• + O2
  • ClO• + O3 -> Cl• + 2O2
  • 2O3-> 3O2
  • Cl• provides an alternative route, activation energy
22
Q

Give the formula for the decomposition of ozone into oxygen

A

2O3 -> 3O2

23
Q

Is the decomposition of the ozone catalysed by chlorine molecules?

A

No

24
Q

Are ozone holes regions of the upper atmosphere where there is a reduced concentration of ozone?

A

Yes

25
Q

State the benefit to life on earth of ozone in the upper atmosphere

A

• Absorbs (harmful) ultraviolet

26
Q

Suggest one reason why the use of CFC’s was not restricted until several years after Rolland and Molina published their research

A

• Lack of evidence that the ozone was being depleted
• Lack of alternatives to CFC’s
• commercial interest to continue to use CFCs
• Hard to obtain international agreement

27
Q

Chloroethane reacts with potassium hydroxide in the presence of propan-1-ol to form ethene.

State the role of potassium hydroxide and the role of propan-1-ol in the reaction

A
  • KOH- Base
  • porpan-1-ol- acts as a solvent
28
Q

Explain why chlorine radical can cause the decomposition of many molecules of ozone

A
  • Cl radical is regenerated and causes a chain reaction in the decomposition of ozone

Organic Chemistry (13 decks)

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