Thanks Jake! Here is an example answer, I tried to condense as much as I could.
HSC (2016)
Question 30 (7 marks)
The use of CFCs has caused ozone depletion in the stratosphere.
Explain the steps that have been taken to reduce this problem. Include relevant chemical equations in your answer.
CFCs have been extensively used in many appliances, though in turn this has led to the destruction of ozone in the stratosphere.
In this region, CFCs photo dissociate in the presence of UV to form chlorine free radicals. As seen in the equations below, this free radical will go on to destroy an ozone molecule, and then create a chain reaction.
CCIF3(g) + UV → Cl. (g) + CF3(g)
Cl. (g) + O3(g) → ClO. (g) + O2(g)
ClO. (g) + O. (g) → Cl. (g) + O2(g)
Because of this, there have been steps taken to reduce this problem. In 1987, the Montreal Protocol was signed which called for cutting CFC use in half by 1998. Though, NASA’s Ozone Trends Panel indicated that the protocol’s limitations were not enough to save the ozone layer, and thus most or all of CFC use would need to be cut.
Thus, substances with a lower ozone depletion potential (ODP) were required to replace CFCs. Today, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are globally used as alternatives to CFCs. This is due to the presence of hydrogen in their structures which enable them to easily break down in the troposphere. This thereby lowers their ODP.
Therefore, the steps take to reduce the use of CFCs have in turn reduced the amount of ozone depletion.
Hey! Good answer; here's how I would have structured it, to engage a bit more in the question, and the additional information I would add/stuff I would leave out.
CFCs were developed in the 1930s to be used as refrigerants. They were widely used, as they were cheap, and easy to produce. However, in 1974 it was demonstrated that CFCs caused Ozone Depletion (in fact, this won the Nobel prize).
Insert Chemical equations you used aboveThe 1985 Vienna Convention, and the 1987 Montreal Protocol, aimed to restrict our use of CFCs. By this time, over 50% of the Ozone concentration over Antarctica had been decimated.
Further, the 1997 Kyoto Protocol required Halon produced to cease by 2010, in line with recommendations made by NASA's Ozone Trends Panel.
From then, countries have agreed to entirely phase out CFCs, which were replaced by HCFCs. However, whilst these HCFCs have a lower ODP, they do not have an ODP of zero. Thus, these too will need to be phased out in favour of HFCs.
An that's it! I suspect my answer is shorter (note that I have ONLY included steps taken to reduce the use of CFCs, rather than sentences containing too much extraneous detail. However, I have included LOADS of information, which is sure to impress the maker).
Again, it is all about making every word of every sentence count. Just load your sentences with information, and make sure to really engage with the question.
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