http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2004exams/pdf_doc/chemistry_04.pdf
Question 27
My answer:
CFC's are very stable. They were developed as coolants for refigerators and were later used in aerosol cans and airconditioners. CFC's were found to have no harm to the environment as it was a colourless, non toxic gas. CFC's however accumulate in the stratosphere and deplete the ozone layer.
CCLF3 (g) + UV light>>> CF3+ CL.
CL. + O3>>>> CLO. + O2
CLO.+O>>> CL.+ O2
The following equations show how the CFC's are broken down by UV light to form chlorine free radicals. The chlorine free radical then attacks another ozone molecule destroying ozone and causing depletion to the ozone layer which is very important to protect life on earth from radiation.
There have been alternative chemicals to replace CFC's. The first alternatives to replace CFC’s were HCFC's. HCFC's also still cause depletion of ozone but we can see from the table that it is much less CFC's. HCFC's have been found to have a lifetime of 121 years in the stratosphere so as a result HCFC's have had much higher ozone depleting potentials then ever thought.
HFC's (hydroflurocarbons) are the second substitute for CFC's. HFC's are viewed as a longer term replacement than HCFC's. This is because these chemicals have an ozone depleting potential of zero as they do not contain chlorine. As seen in the table, there is no depletion of HCF's making it a good alternative.
HCFCs and HFCs are much less durable than CFCs in the lower atmosphere because they contain hydrogen atoms in their molecular structure, are thus less likely to persist and carry their ozone-destroying chlorine and fluorine atoms into the stratosphere. HFC's contain C-H bonds so undergo some decomposition in the troposphere, and contain no C-Cl bonds so do not form Cl atoms in the stratosphere. Consequently their ozone destroying capacity is much less than that of CFC's.
The structure of HCF's makes HFC's very similar to CFC's structure therefore it is useful as an alternative to refrigeration.
HFC's are effective in that they do not accumulate in the atmosphere to the same extent as CFC's and therefore do not cause as much damage to the ozone layer, hower As the atmospheric concentrations of HCFC's and HFC's are increasing rapidly, they are causing an international concern about greenhouse gas global warming. HFC's now account for 10 % contribution to global warming.This means that HFC's should be used temporarily to replace CFC's but may not be effective in the long term.
What mark would i get ?
Question 27
My answer:
CFC's are very stable. They were developed as coolants for refigerators and were later used in aerosol cans and airconditioners. CFC's were found to have no harm to the environment as it was a colourless, non toxic gas. CFC's however accumulate in the stratosphere and deplete the ozone layer.
CCLF3 (g) + UV light>>> CF3+ CL.
CL. + O3>>>> CLO. + O2
CLO.+O>>> CL.+ O2
The following equations show how the CFC's are broken down by UV light to form chlorine free radicals. The chlorine free radical then attacks another ozone molecule destroying ozone and causing depletion to the ozone layer which is very important to protect life on earth from radiation.
There have been alternative chemicals to replace CFC's. The first alternatives to replace CFC’s were HCFC's. HCFC's also still cause depletion of ozone but we can see from the table that it is much less CFC's. HCFC's have been found to have a lifetime of 121 years in the stratosphere so as a result HCFC's have had much higher ozone depleting potentials then ever thought.
HFC's (hydroflurocarbons) are the second substitute for CFC's. HFC's are viewed as a longer term replacement than HCFC's. This is because these chemicals have an ozone depleting potential of zero as they do not contain chlorine. As seen in the table, there is no depletion of HCF's making it a good alternative.
HCFCs and HFCs are much less durable than CFCs in the lower atmosphere because they contain hydrogen atoms in their molecular structure, are thus less likely to persist and carry their ozone-destroying chlorine and fluorine atoms into the stratosphere. HFC's contain C-H bonds so undergo some decomposition in the troposphere, and contain no C-Cl bonds so do not form Cl atoms in the stratosphere. Consequently their ozone destroying capacity is much less than that of CFC's.
The structure of HCF's makes HFC's very similar to CFC's structure therefore it is useful as an alternative to refrigeration.
HFC's are effective in that they do not accumulate in the atmosphere to the same extent as CFC's and therefore do not cause as much damage to the ozone layer, hower As the atmospheric concentrations of HCFC's and HFC's are increasing rapidly, they are causing an international concern about greenhouse gas global warming. HFC's now account for 10 % contribution to global warming.This means that HFC's should be used temporarily to replace CFC's but may not be effective in the long term.
What mark would i get ?
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