Name: Rosemarie Simard-Michot 40256352 Student number: 1st Assignment for CHEM 283 A. Basics of Photochemistry (14) 1. Draw a graph of the absorption spectrum of ozone in the gas phase. Make sure to appropriately label the graph’s axes, including units. (3) 2. The splitting of ozone into diatomic oxygen and an oxygen atom requires 105 kJ/mol. What is the maximum wavelength of light that has that much energy? (1) πΈ= βπ λ 1000π½ 1ππ½ 105 ππ½/πππ × 1 πππ × 6.022×10 ππππππ’πππ −34 βπ λ= πΈ = (6.62607015 × 10 π½/πππ 8 −19 λ ≈ 1. 14 × 10 −19 π½•π )(3.00×10 π/π ) 1.74 ×10 −7 = 1. 74 × 10 23 π½/πππ πππ‘πππ ππ 114 ππ 3. What is the name of the corresponding wavelength region? (1) The corresponding wavelength of 114nm would fall within the ultraviolet region (UV), most specifically the UV-C which ranges between 100nm to 280nm. 4. Why does light with this wavelength not bring about a splitting of ozone? (1) Light with a wavelength of 114nm is usually energetic enough to slip the ozone molecule into dioxygen and oxygen atoms. 5. Explain why the photolytic destruction of ozone requires light of a maximum wavelength of 320 nm. (1) The energy of the absorption of the ultraviolet to destroy the ozone must overcome the activation energy barrier required to break the oxygen bonds. Longer wavelengths such as UV-A and visible light do not have sufficient energy to overcome this activation energy barrier and therefore cannot initiate the photolytic destruction of ozone. In the contrary, UV-B (280nm-315nm) has enough energy to break the bond in ozone molecules. 6. Calculate the energy in units of kJ/mol corresponding to that light. (1) πΈ= βπ λ −34 = 6.626×10 8 × 3.00×10 −9 320×10 −19 (6. 198 × 10 −19 = 6. 198 × 10 π½ 23 ππ½/ππππππ’ππ) × (6. 022 × 10 ππππππ’πππ /πππ) = 373. 55ππ½/πππ 7. Let’s assume that light with a wavelength of 280 nm is absorbed by an ozone molecule, which causes it to split into diatomic oxygen and an oxygen atom. How much excess energy is there after the reaction? What happens to it? (3) 1. calculate the energy of the absorbed photon −34 πΈ= 6.626×10 8 × 3.00×10 −9 280×10 π −19 = 7. 09 × 10 π½ 2. Bond energy products of diatomic oxygen is approximately 498 kJ/mol 3. Calculate excess energy πΈπ₯πππ π ππππππ¦ = πΈπππππ¦ ππππ πππππ πβππ‘ππ − πππ‘ππ ππππ ππππππ¦ ππ πππππ’ππ‘π −19 = 7. 09 × 10 −19 = 7. 09 × 10 3 3 π½ − (2 × (498 × 10 )) π½/πππ + (498 × 10 )π½/πππ −19 π½ − 9. 96 × 10 π½ = − 2. 869 × 10 −19 π½ 8. Give three different reactions that the O formed in this reaction might undergo. (3) 1. Recombination with oxygen molecules involving one oxygen atom combinin with a molecule of diatomic oxygen to form ozine. 2. Reacting with another oxygen atom to form dioxygen. 3. Reacting from another molecule to form an oxide. B. Ozone Depleting Substances (16) 1. Give the IUPAC names for the following four substances: CCl4, CHCl3, CH2Cl2, CH3Cl. (2) CCl4: Carbon Tetrachloride CHCl3: Chloroform CH2Cl2: Dichloromethane CH3Cl: Chloromethane 2. All four substances had commercial uses. List one of them for each. (2) Carbon Tetrachloride (CCl4): It is used as a solvent for oils and fats, as a refrigerant, and in fire extinguishers. Chloroform (CHCl3): It is used as an anesthetic and as a solvent in various industrial processes. It's also used in the production of refrigerants and pesticides. Dichloromethane (CH2Cl2): It is used as a solvent in paint stripping, degreasing, and as a process solvent in the pharmaceutical industry. Chloromethane (CH3Cl): Chloromethane is used as a methylating agent in organic synthesis, as a solvent in various applications, and in the production of silicone polymers. 3. Study the following information on CFC naming system by yourself and then use the naming convention for CFCs, deduce the code for the four substances in question C1. (2) Carbon Tetrachloride (CCl4): CFC-11 Chloroform (CHCl3): CFC-11 Dichloromethane (CH2Cl2): CFC-12 Chloromethane (CH3Cl): CFC-11 4. Read and study the following paper. What structural features of CFCs contribute most to the ozone depletion potential. Rank these four substances in a sequence of decreasing ozone-depletion potential and explain your ranking. (2) Carbon Tetrachloride (CCl4): It has the highest number of chlorine atoms among the four substances, leading to a high potential for ozone depletion. It also has a long atmospheric lifetime, contributing further to its ozone-depletion. Chloroform (CHCl3): It has fewer chlorine atoms compared to carbon tetrachloride but still contributes significantly to ozone depletion due to its chlorine content. It also has a longer atmospheric lifetime compared to the other substances. Chloromethane (CH3Cl): It has only one chlorine atom, which reduces its ozone-depletion potential Its atmospheric lifetime is shorter than that of chloroform, reducing its contribution to ozone depletion. Dichloromethane (CH2Cl2): It contains two chlorine atoms, which is fewer than carbon tetrachloride but more than chloroform and chloromethane. 5. Rank the following substances, in a sequence of increasing ozone-depletion potential and explain your ranking: CF3Br, CF2ClBr, CF2Cl2. (3) CF3Br (Bromotrifluoromethane):This compound contains bromine, which is highly reactive and efficient at catalytically destroying ozone in the stratosphere. Therefore, CF3Br has the highest ozone-depletion potential. CF2ClBr (Dichlorobromofluoromethane): This compound contains both chlorine and bromine atoms. Bromine is even more reactive than chlorine in depleting ozone, so compounds containing bromine have higher ozone-depletion potentials. CF2Cl2 (Dichlorodifluoromethane): It contains chlorine atoms which when it reaches the stratosphere can release chlorine radicals upon photolysis, which can destroy ozone molecules. However, it's less reactive compared to substances containing both chlorine and bromine, so its ozone-depletion potential is relatively lower. 6. Rank CFC-13, CFC-12, CFC-21, CFC-22, CFC-31 and CFC-30 in a sequence of decreasing ozone depletion potential and explain your ranking. (5) CFC-22 : It contains two chlorine atoms, making it more reactive and hence more potent at depleting ozone compared to the other compounds in the list. CFC-12 : It also contains two chlorine atoms, similar to CFC-22, so it has a high ozone depletion potential. CFC-21 : It contains only one chlorine atom, making it less potent in depleting ozone compared to CFC-12 and CFC-22. CFC-13 : It contains one chlorine atom, which is fewer than CFC-12 and CFC-22. CFC-30 : It also contains one chlorine atom but in a different structural arrangement compared to CFC-13. However, since it contains only one chlorine atom, its ozone depletion potential is expected to be lower than that of CFC-12 and CFC-22. CFC-31: It contains only one chlorine atom, similar to CFC-13 and CFC-30. However, its structural arrangement is different, and its ozone depletion potential is expected to be lower than CFC-12 and CFC-22, but possibly slightly higher than CFC-13 and CFC-30. C. Ground-level ozone in our city Montreal (10) Montreal has a network of measuring stations located on the Island of Montreal that allows the continuous determination of the atmospheric concentration of several pollutants. Get the 2022 (latest available) dataset of the monitoring results from https://www.donneesquebec.ca/recherche/dataset/vmtl-rsqa-polluants-gazeux. Based on the data, make your best inference on whether the ground-level ozone formation in Montreal is VOC limited or NOx limited? Is there any difference between different locations? Is there any difference for different months/seasons? While you can probably easily get the answers from Google but your answers to the questions need to be datadriven. You can also get other dataset to support your answers. Integrate your answers to the above questions and write a briefing note which is “an essential tool for conveying information and for contributing to the decision-making process in all government departments and agencies. It is used to explain and express ideas, target sources of concern, analyze issues, provide advice, make recommendations and seek decisions. For accountability reasons all government decisions are based on written documents”. A Practical Guide To Writing Briefing Notes can be found here: https://www.naadsn.ca/wp-content/uploads/2020/08/dsfg_policy_brief_writing_guide_v2.pdf State clearly how you used the data to reach your conclusions. Based on your analysis, how would you advice the decision makers in order to further reduce the ground-level ozone concentrations and occurrence of photochemical smog in our city? Note: a general briefing note should not be over two pages including key figures and/or tables that support your statements.
