Chlorofluorocarbons chemical destruction

A major concern with chlorofluorocarbons is destruction of the ozone layer (mentioned in"Chemical Connections Freons Tn this chapter).The ozone-consuming reactions are thought to occur through a radical chain mechanism. The production of one radical species derived from a CFC can destroy a large number of ozone molecules before any termination steps occur. 

The other global environmental problem, stratospheric ozone depletion, was less controversial and more imminent. The U.S. Senate Committee Report supporting the Clean Air Act Amendments of 1990 states, Destruction of the ozone layer is caused primarily by the release into the atmosphere of chlorofluorocarbons (CFCs) and similar manufactured substances—persistent chemicals that rise into the stratosphere where they catalyze the destruction of stratospheric ozone. A decrease in stratospheric ozone will allow more ultraviolet (UV) radiation to reach Earth, resulting in increased rates of disease in humans, including increased incidence of skin cancer, cataracts, and, potentially, suppression of the immune system. Increased UV radiation has also been shown to damage crops and marine resources."... 

Chemical Family a group of elements that share similar chemical properties and share the same column in the periodic table, for example, halogens, alkali earth Chirality condition that describes the handedness of a molecule or whether a molecule exists in forms that can be superimposed on each other Chlorofluorocarbons also called CFCs, compounds consisting of chorine, fluorine, and carbon that are responsible for stratospheric ozone destruction Coagulation precipitation or separation from a dispersed state Coefficient of Thermal Expansion measure of the rate at which a substance will expand when heated... 

Oxidizer Chemical substance that causes oxygen to combine with another chemical substance examples include oxygen and hydrogen peroxide Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of ozone layer is due to the breakdown of certain chlorine- and/or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules Ozone layer Protective layer in the atmosphere, about 15 miles above the ground. The ozone layer absorbs some of the sun s ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the Earth s surface PAHs Polycyclic aromatic hydrocarbons... 

The ozone question is complicated by the fact that other chemicals are implicated in its destruction. Chlorofluorocarbons were formerly widely used as propellants in spray cans, and they continue to be used as refrigerants.3 They are extremely stable and long-lived in the environment. However, they too can undergo photolysis in the... 

Describe the chemical reactions that drive the destruction of various chlorofluorocarbons in the stratosphere. 

Chlorofluorocarbons have unique chemical and thermodynamic properties that make them very attractive for a wide variety of applications, ranging from refrigeration and air conditioning to foam blowing and medical sterilants. Unfortunately, as mounting evidence shows, their inertness allows CFCs to be transported to the stratosphere, where their photolysis releases chlorine atoms that participate in catalytic ozone destruction. Consequently, the manufacture and use of these compounds is being phased out. 

Ozone (O3) exists in the atmosphere, 20-40 km above sea level. Ozone absorbs UV radiation which would otherwise harm living things. The effects of ozone loss could include increased human cataracts and skin cancer, reduction of plankton in ocean waters and destruction of plants, including crops. Ozone layer destruction in the Antarctic was reported in 1985 a major cause of this was believed to be the release of chlorofluorocarbon compounds, such as CCI2F2 (CFCs). These compounds are chemically unreactive, non-toxic and odourless, properties which at one time caused them to be used as solvents, aerosol propellants, refrigerant fluids and blowing agents for expanded plastic foams. They are so stable, however, that they persist in the atmosphere for years and eventually enter its upper layers, where they are broken down by the powerful UV radiation emitted by the sun. Their decomposition products can then destroy ozone ... 

Packaging materials are all, to varying extents, damaging to the environment. For example, the manufacture of poly(styrene) (PS) products involves the use of a variety of hazardous chemicals and starting materials, such as benzene, a known mutagen and a probable carcinogen. Chlorofluorocarbons have also been used in the manufacture of blown or expanded PS products. Chlorofluorocarbons have been linked to the destruction of the ozone layer. 

We noted from the outset of this chapter that environmental concerns about ozone depletion arise from tbe increase in the rate of destruction of ozone in the stratosphere. This is a process apparently caused by man-made chemicals. Specifically, chlorofluorocarbons used as refrigerants have been cited as a cause of ozone depletion. Yet a look at the Chapman cycle does not show any obvious role for CFCs. So how can these molecules accelerate the destruction of ozone if they do not even appear in the underlying chemical equations Catalysis is a process in which a reaction rate is influenced by the presence of substances that are neither reactants nor products in the overall equation. A catalyst is a substance that increases the rate of the reaction but is neither created nor destroyed in the process. How can CFCs catalyze ozone depletion ... 

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