Ozone depletion and CFCsAQA A-Level Chemistry: Flashcards
What these 12 flashcards ask
- Why is ozone in the upper atmosphere beneficial?
- Why were CFCs used as solvents and refrigerants?
- How are chlorine atoms formed from CFCs?
- Write the equation for the formation of Cl· from CCl₂F₂.
- What is homolytic fission?
- Write the first step of the catalytic decomposition of ozone by chlorine.
- Write the second step of the catalytic decomposition of ozone by chlorine.
- What is the overall equation for ozone decomposition by chlorine atoms?
- Why is Cl· described as a catalyst?
- Which species is the intermediate in the chlorine cycle?
- Why did legislation banning CFCs follow?
- Why do chlorine-free alternatives such as CH₂FCF₃ not damage the ozone layer?
Exam questions on Ozone depletion and CFCs
- Ozone, O₃, forms naturally in the upper atmosphere. Dichlorodifluoromethane, CCl₂F₂, is a chlorofluorocarbon (CFC) that was widely used as a refrigerant, and its molecules can drift up into the same region of the atmosphere.Write an equation for the formation of a chlorine atom from CCl₂F₂ and state the type of bond fission involved.2 marks
- Chlorine atoms in the upper atmosphere decompose ozone by a two-step sequence:
Cl· + O₃ → ClO· + O₂
ClO· + O₃ → 2O₂ + Cl·Explain why one chlorine atom can lead to the decomposition of many ozone molecules.2 marks
- Until the 1980s CFCs were widely used as solvents and refrigerants. In 1985 researchers working in Antarctica reported unexpectedly low ozone concentrations above the continent. Other research groups, using different measuring methods, then published their own results.Explain how the results of research by different groups provided evidence that led to legislation banning CFCs.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).