TEST 1 APCH 11 (01) Review, Solutions & Feedback
Question 1 What is the concentration of nitrogen in the atmosphere (0 C and 1 atm) in g/l? N in the atmosphere ~ 78% Gas concentration unit s means that there are 78 mol of N for every 100 mol of air Convert moles of N to a mass: mass N = 78 mol 8. 014g 1mol = 185. 045g Convert moles of air to a volume: V = nrt P = 100 mol 0. 0806 L atm K 1 mol 1 9. 15 K 1 atm = 405. 6 L Ans = 0.908 g/l R: 78 moln 100 mol air 8.014gN 1molN 1mol air 4.056L = 0. 908gL 1
Question a) Label region 1-4 on the following Region 1 Region Region diagram Region 1 Thermosphere (Exosphere) Region Region Mesosphere Stratosphere (0.5 points) (0.5 points) (0.5 points) Region 4 Region 4 Troposphere (0.5 points)
Question b) What are the main constituents in region 4 (give approximate percentages) ( points) 78% N, 1%, 0.1 % Ar, and 0.04% C (or H ~ 0.5-5%) xygen and zone ( and )
Question d) What is the greenhouse effect, and what are its beneficial outcomes and potential disastrous impacts? (5 points) Certain gases in the atmosphere absorb and re-emit IR radiation out to space and towards the planet s surface The IR energy that is re-emitted towards the ground warms up the planet s surface It is the reason why earths average surface temperature is 15 C, and thus able to have liquid water on the surface. Without the natural greenhouse effect, the surface of the earth would be below freezing If the greenhouse effect becomes un-balanced, this can cause global warming, and lead to extreme climate
Question e) Explain the temperature trends in region and 4. (4 points) Region (Stratosphere): Formation and destruction of ozone via various photochemical processes releases a large amount of kinetic & thermal energy, this energy is responsible for the increase in temperature with increase in altitude Region 4 (Troposphere) The main heating effect in the troposphere is from IR energy released by the surface (some heating by EM-radiation from the sun) As warm air rises it cools, thus giving a general cooling trend as we increase in altitude As warm air rises, it expands since the pressure decreases Expansion means the gas molecules in any rising parcel of air must do work Since the gas molecules are doing work, there is a loss of kinetic energy Since there is no transfer of heat, this is an adiabatic process (aka adiabatic cooling rate ~ 10C/1000m)
Question Carbonyl sulfide (CS) is present as a trace gas in the atmosphere at a concentration of 0.84 ppb; its major source are the oceans, from which it enters the atmosphere at a rate of 6 x 10 8 kg/year. What is the residence time (in years) of CS in the atmosphere? (Assume the total volume of the atmosphere is 4. x 10 1 L) Vol of air 0.84 ppb of CS occupies [10 points] 0.84 ppb CS ~ 0.84 Moles CS in 1x10 9 moles air: 0. 84 mols CS 60.0751gCS 1mol CS = 50. 46084 g CS V = nrt P = 1 109 mol 0. 0806 L atm K 1 mol 1 88. 15 K 1 atm =. 656 10 10 L 50. 46084 gcs 645589000L air 4. 101 L = 8. 98474 10 1 g How long will it take to get it all out?!? 8. 98474 10 09 kgcs 6 10 8 kgyear 1 = 14. 97years
Question.Alternative Method!!! 0.84 ppb can be used as a fraction! Since with gases it s always mol vs mol, or L vs L 0. 84 10 9 CS 4. 10 1 L 1. 0atm 0. 0806 L atm K 1 mol 1 88. 15K = 14. 97 years 60. 0751gCS 1mol CS 1. 0kg 1000g 1year 6 10 8 kg
Question 4 What are the chapman reactions (give full equations)? [5 points] Set of equations first proposed by Chapman to describe the mechanism for the destruction and formation of ozone in the stratosphere * h M M h
Question 5 a) What is the difference between London smog and photochemical smog? ( points) London smog: Mixture of S, carbon particles & water vapour The S in the mixture gave the smog a slightly acidic & reducing properties hence sometimes referred to as reducing smog Photochemical or Los Angeles Smog Mixture of hydrocarbons and Nx Mainly oxidizing in nature Aerosols are mainly complex hydrocarbons as opposed to mainly carbon particles
Question 5 Describe the conditions and processes responsible for photochemical smog (give chemical equations and main irritant). (8 points) CH CH CH CH H( CH C N( CH CH C N ) CH CH CH Large urban area with numerous motor vehicles and other hydrocarbon combustion sources to produce N, VCs, & reactive hydrocarbons Need lot of sunlight and warmth to drive the main reactions Geological area prevents good circulation of air masses (inversion Warm air sits on top of cooler air) Generally during rush hour, large amounts of N, ozone, and oxygen radicals produced Sunlight drives production of H radicals from ozone and nitrous acid present VCs, N, & other radicals from vehicular traffic produce various aldehydes Further photochemical reactions, especially with the increasing amount of aldehydes, produces more radicals, especially H,, eventually produce significant amounts of PAN ) CH H CH CH CH C H C CN H CH H N
Question 6 a) What is meant by the term acidic deposition? ( points) General term applied to any form of wet precipitation, usually in the troposphere, with acidic species stronger than C xides of nitrogen (N), and sulphur (S )
Question 6 c) Summarize the reactions responsible for the formation of a sulfur based acidic species over Durban at 7:50 am on a typical workday. (8 points) S + H + M HS + M Homogenous HS + + M H + S + M S + H H S 4 Heterogeneous S g S aq S aq + H HS aq + H + (aq) - H HS aq + H S (aq) + H + (aq) S HS aq + H HS (aq) + H H