what do you know about CFCs?

Question

i have to gather some information about CFCs and i need your help . thank you!

Answer 1

The haloalkane (also known as halogenoalkanes) are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, such as chlorine or fluorine, making them a type of organic halide. They are known under many chemical and commercial names. As fire extinguishants, propellants and solvents they have or had wide use. Some haloalkanes have negative effects on the environment such as ozone depletion. The most widely known family within this group are the chlorofluorocarbons (CFCs).

Since the late 1970s the use of CFCs has been heavily regulated because of its destructive effects on the ozone layer. This damage was discovered by Sherry Rowland and Mario Molina, who first published a paper suggesting the connection in 1974. It turns out that one of CFCs' most attractive features—their unreactivity—has been instrumental in making them one of the most significant pollutants. CFCs' lack of reactivity gives them a lifespan which can exceed 100 years in some cases. This gives them time to diffuse into the upper stratosphere. Here, the sun's ultraviolet radiation is strong enough to break off the chlorine atom, which on its own is a highly reactive free radical. This catalyses the break up of ozone into oxygen by means of a variety of mechanisms, of which the simplest is:

Cl· + O3 → ClO· + O2
ClO· + O3 → Cl· + 2 O2
Since the chlorine is regenerated at the end of these reactions, a single Cl atom can destroy many thousands of ozone molecules. Reaction schemes similar to this one (but more complicated) are believed to be the cause of the ozone hole observed over the poles and upper latitudes of the Earth. Decreases in stratospheric ozone may lead to increases in skin cancer.

In 1975, the US state of Oregon enacted the world's first ban of CFCs (legislation introduced by Walter F. Brown). The United States and several European countries banned the use of CFC's in aerosol spray cans in 1978, but continued to use them in refrigeration, foam blowing, and as solvents for cleaning electronic equipment. By 1985, scientists observed a dramatic seasonal depletion of the ozone layer over Antarctica. International attention to CFCs resulted in a meeting of world diplomats in Montreal in 1987. They forged a treaty, the Montreal Protocol, which called for drastic reductions in the production of CFCs. On March 2, 1989, 12 European Community nations agreed to ban the production of all CFCs by the end of the century. In 1990, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by the year 2000. By the year 2010 CFCs should be completely eliminated from developing countries as well.

Because the only available CFC gases in countries adhering to the treaty is from recycling, their prices have gone up considerably. A worldwide end to production should also terminate the smuggling of this material, such as from Mexico to the United States.

A number of substitutes for CFC's have been introduced. Hydrochlorofluorocarbons (HCFCs) are much more reactive than CFC's, so a large fraction of the HCFCs emitted break down in the troposphere, and hence are removed before they have a chance to affect the ozone layer. Nevertheless, a significant fraction of the HCFCs do break down in the stratosphere and they have contributed to more chlorine buildup there than originally predicted. Development of non-chlorine based chemical compounds as a substitute for CFCs and HCFCs continues. One such class are the hydrofluorocarbons (HFCs), which contain only hydrogen and fluorine. One of these compounds, HFC-134a, is now used in place of CFC-12 in automobile air conditioners.

There is concern that halons are being broken down in the atmosphere to bromine, which reacts with ozone, leading to depletion of the ozone layer (this is similar to the case of chlorofluorocarbons such as freon). These issues are complicated: the kinds of fires that require halon extinguishers to be put out will typically cause more damage to the ozone layer than the halon itself, not to mention human and property damage. However, fire extinguisher systems must be tested regularly, and these tests may lead to damage. As a result, some regulatory measures have been taken, and halons are being phased out in most of the world.

In the United States purchase and use of freon gases is regulated by the Environmental Protection Agency, and substantial fines have been levied for their careless venting. Also, licenses, good for life, are required to buy or use these chemicals. The EPA website discusses these rules in great detail, and also lists numerous private companies that are approved to give examinations for these certificates.

There are two kinds of licenses. Obtaining a "Section 609" license to use CFCs to recharge old (pre-1993 model year) car air conditioners is fairly easy and requires only an online multiple choice test offered by several companies. Companies that use unlicensed technicians for CFC recharge operations are subject to a US$15,000 fine per technician by the EPA.

The "Section 608" license, needed to recharge CFC-using stationary and non-automobile mobile units, is also multiple choice but more difficult. A general knowledge test is required, plus separate exams for small size (such as home refrigerator) units, and for high and low pressure systems. These are respectively called Parts I, II, and III. A person who takes and passes all tests receives a "Universal" license; otherwise, one that is endorsed only for the respectively passed Parts. While the general knowledge and Part I exams can be taken online, taking them before a proctor (which has to be done for Parts II and III) lets the applicant pass these tests with lower scores.

Answer 2

cfc stands for chlorofluorocarbons
they were used in aerosols in the past, but then they found out that they produced free radicals that destroyed ozone which has the chemical formula O3
CFC's are now banned from use, however their effect is still noticed because it takes many years for them to disappear from the atmosphere, i think around 30-50yrs or so

Answer 3

They were used as a refrigerant and a propellant for aerosols. They are still used as cleaners in the computer chip industry. The pharmaceutical industry will sometimes use them as a solvent for their extractions. The EPA has them listed as Hazardous Air Pollutants (HAP's)

Answer 4

For the record, the answer given by prakash_s is a direct quote of an entire section from Wikipdeia.

http://en.wikipedia.org/wiki/Chlorofluorocarbon

If you scroll down to "Environmental Issues" you will find his "answer" verbatim.

Not that it matters, but we shouldn't reward people in any way I think for plagiarism.