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1) Organic compound

- Carbon

- Chlorine

- Fluorine

2) Produced as a volatile derivative of

- Methane

- Ethane

- Formulae CClmF4-m & C2ClmF6-m (m is nonzero)

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3) A family of non-toxic

4) Inert chemical compounds bound tightly to forminert molecules

5) Invented in the late 1920s & early 1930s as a safer

alternative to :

- Sulfur dioxide & ammonia refrigerants

6) Some commercial names of CFCs

- Freon , Algofrene, Arcton, Daiflon, Eskimo, FCC,

Flon, Flugene, Forane, Fridohna, Genetron,

Isceon, Isotron, Kaiser,Ledon, Racon, & Ucon.

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7) Used worldwide in

- Aerosol sprays (banned in the U.S. & a fewnorthern European countries in the mid-70s)

- Coolants in refrigeration system & air

conditioners

- Solvents to clean electronic components

(eg washing micro-electronic chips)

- Blowing agents in the production of plastic

foams

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8) Chosen because

- Low toxicity

- Nonflammable

- Noncorrosive

- Nonreactive with other chemical species

- Desirable thermal conductivity & boiling point

9) Each kind of CFC has a different formula such as

- CFC 11: CCl3F (Trichlorofluoromethane)- CFC 12: CCl2F2 (Dichlorodifluoromethane)

- CFC 22: CHClF2 (Chlorodifluoromethane)

- CFC 113: C2Cl3F3 (Trichlorotrifluoromethane)

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1) A common subclass of Chlorofluorocarbon

2) Contain

- Carbon

- Hydrogen

- Chlorine- Fluorine

- Formulae CClmFnH4-m-n & C2ClxFyH6-x-y,

(m, n, x, & y are nonzero)

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3) Not found anywhere in nature

4) HCFC production increased after countries

agreed to phase out the use of CFCs.

5) However, most HCFCs are broken down in the

lowest part of the atmosphere which pose a much

smaller risk to the ozone layer.

6) Also a very potent greenhouse gas

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ultra-violet

radiationfrom the Sunis absorbed bystratosphericozone and,doesn't enter

thetroposphere.

ultra-violetlight is tooweak tobreakdown the

CFC's presentthere

However,significantamounts enteredthe stratospherewhere the ultra-violet radiationis strong enough

to break themdown into veryreactive chlorineand fluorineradical species.

Theseradicalsare capableof destroying

ozone

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This meansthat they arenot consumed

by thereaction butare recycledand cancontinue toreact with

other ozonemolecules todestroy themas well.

However,chlorineradicals (Cl)

react withozone simply todestroyit. They arevery efficientat removing

ozone becausethey act ascatalysts.

So as ozoneconcentrationsincrease, theamount ofozone destroyed

also increases.

Under

naturalconditions,ozone levelsare constant since theyare both

formed &destroyedby ultra-violet light.

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Molecular chlorine (Cl2) is a stable molecule which

does not react with the ozone.

However, when the CFC reach the ozone layer, 2

reactions happen.

The first involves homolytic breakdown of CFC

molecules under the influence of ultraviolet light

CCl2F2 CCl2F2 + Cl

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This reaction produces highly reactive chlorine

free radical

The atom may recombine with its original

molecule or may attack a molecule of the ozone

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1) Choose CFC - free products for your household

2) If you own or work for a business, ensure that

your

company supplies and products are as free ofCFCs

as possible

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4) Attempts have been made to develop compounds

which have low ozone depletion potential (ODP) to

replace CFCs as refrigerants, aerosol propellantsand solvents. Possible alternatives for CFCs

include:

Hydrochlorofluorocarbons (HCHCs) such as

CF3CHCl2

They break down more quickly in the atmosphere.

Though they have a lower percentage ofchlorine and hence a lower ozone depletion

potential than CFCs, they could damage ozone if

overuse.

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Hydrofluorocarbons(HCFs) such as CF3CH2F

They have no chlorine and thus are "ozone safe".

However, safety question on toxicity is still unsolved.

Hydrocarbons such as butane and propane

They are cheap and readily available. As they

contain no chlorine, they are "ozone safe". However,they are flammable and poisonous.

Water and steam

They are effective for some cleaning applicationsand thus can replace some CFCs as solvents incleaning.

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5) Installation of recovering and recycling units

to recycle CFCs from used refrigeration systems

and motor vehicle air conditioners to control theventing of CFCs into the atmosphere.

6) World wide help

Hong Kong joined the international effort to

protect the ozone layer by becoming a party to the

Protocol and introduced the Ozone Layer

Protection Ordinance (OLPO) in 1989. Theordinance empowers the government to control

the consumption of CFCs and other ozone

depleting substances through import/export

licensing control.

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As early as 1978, CFC aerosol propellants were

banned in some countries like Canada and United

States. The first international effort to protect theozone layer came in January 1978 when 24

countries signed the Montreal Protocol on

Substances That Deplete the Ozone Layer which

called for a cut back of the CFC production instages. The Protocol was amended in 1990 when 93

countries pledged to stop all production of CFCs

and other ozone depleting substances by 2000.

Since then, many industrialized nations have

agreed to a complete phase out as early as 1995.

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Done by,

Thava Muthasha

Ho Min YenGeetha Sarika

Nashwa