Hello I have a midterm and need help trying to uderstand the questions to answer
ID: 905854 • Letter: H
Question
Hello I have a midterm and need help trying to uderstand the questions to answer. Can you help with questions #2-9 and explain. Thank You
1. (40) i. Describe the earths atmosphere. Include the regions up to and including the thermosphere. Include the pressure and temperatures (approximate - in each region) vs distance and the changes that occur in each region.
ii. Describe some of the chemistry that occurs for pollution and initiation of reactions in the troposphere.
iii. Describe some of the chemistries you feel are important in the stratosphere and why ?
2. (30) Describe how an inversion occurs and include what the relative densities of the different layers of the troposphere when an inversion is likely to occur (ii.) how you would calculate the density (assuming a constant pressure through both layers) and what the density has to do with the inversion.
3. (30) Calculate DHrxn for the following reactions and indicate if they are likely to go in forward or reverse direction.
What Reaction (s) may occur in the troposphere or in the stratosphere.
NO2 + O3 = NO3 + O2
NO2 + Br = BrO + NO
CO2 + H2 = CO + H2O (g) syn gas reaction CO2 (-94) CO (-26) H2O (g) (-58.5) H2O (l) ( -69) Br (24) , O3 (34)
CO2 + H2 = CO + H2O (l) syn gas reaction Hf data: NO (21.5) NO2 (8.0) NO3 (17.5) BrO (26.5) kcal mol-1
4, (35) Given the current level of CO2 in the atmosphere is 380 ppm
(i.) Calculate the pH of rain water due to the CO2.
(ii.) If the levels of CO2 continue to increase will the pH also increase?
5, (40) Calculate the concentrations in different units:
(i.) How many grams of Acetic Acid CH3CO2H are needed to make a solution of 0.1 mole / liter
(ii.) What is the concentration of Ethanol (C2H5OH) in (PPM)m that is 1 microgram ethanol per liter of water?
(iii). What is the concentration of 1 microgram Ethanol liquid per liter of water in moles/liter ?
(iv.) 120 ppb benzene (C6H6) in air in units of milligrams / M3
(Note: v stands for volume in PPMv and m stands for mass in (PPM)m).
6. (25) Calculate the ratio of carbon 14 to the initial carbon 14 concentration in an fossil that is thought to be 1500 years old. Use the half life of C14 as 1245 years.
7, (30) (i.) Describe the reactions needed to convert methane (CH4) into CO2 in the photochemistry and pollution chemistry of the troposphere.
ii.) Indicate which reactions are abstraction and which are association. (note some reactions may not be one of these two classes of reaction)
8. (35) Calculate the energy of light needed to dissociate Ozone: O3 ® 3PO + 3O2 (I) and
Calculate the energy of light needed to dissociate Ozone: O3 ® 1DO + 3O2 (II)
What is the wavelength of the first reaction (include units)
What are the implications of forming 1DO in the troposphere or the stratosphere.
Enthalpy data DfH 1DO 81. 3pO 58.45, O3 34.5, kcal mol-1 3O2 (0.0) = ground state O2
9, (25) What are the sources (source chemical reactions including species in the reactions)
of: (i.) OH and (ii.) Peroxy Radical CH3OO in the troposphere ?
Explanation / Answer
5) 1) CH3COOH
molecular weight = 60
we need 0.1 M of acetic acid
so we need 0.1*60 = 6 g/l
5)2) 1 microgram = 10 -6 g
10 -6 grams * 1000 =10 -3 mg/l
IN PPM = 0.001 ppm
5)3) 10 -6 g of ethanol in 1 litre of water .
no. of moles of ethanol = 10 -6 g/46 present in 1 liter of water.
= 0.022*10 -6 moles in 1 litre of water.
5)4) 1 ppb =0.001mg in 1 litre of air
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