Spring 2001                             CHE 431/ENS 447                  Name________________

Sample Test #1

Ch 1-3; Baird

 

Useful information

 

E = hn              PV=nRT          Vsphere = 4/3 pr3                       Asphere = 4pr2    

1 atm = 2 x 1018 molecules/cm3

 

Show all work on problems and give units for each numerical answer.

 

Part One:  Fill in the Blank/Multiple choice (3 points each).

 

1.                  Tropospheric ozone formation is favored when

 

I    [O2] is low              III  [NO] is high

II  [NO] is low             IV  [NO2] is high

 

(a)    I and II

(b)   I and III

(c)    II and III

(d)   II and IV

(e)    I, II, and IV

(f)     all

(g)    none

 

2.                  Calculate the energy of a photon of infrared light with l = 1000 nm.

 

(a)    3.3 x10-43 J/photo

(b)   2 x10-19 J/photon

(c)    1 x105 J/photon

(d)   2 x10-37 J/photon n

(e)    1 x10-5 J/photon

 

3.                  The concentration of CO in the atmosphere is approximately 0.2 ppm.  What is the concentration in molecules/cm3?

 

(a)    4 x1011 molecules/cm3

(b)   4 x1017 molecules/cm3

(c)    1 x10-25 molecules/cm3

(d)   1 x1017 molecules/cm3

(e)    2.4 x1041 molecules/cm3

 

4.                  A _secondary_ pollutant is one that is formed by reactions in the atmosphere.

 

5.                  The _mesosphere_ region of the atmosphere extends from 50-90 km above the surface of the earth.

 

6.                  Which molecules serve as “chlorine reservoirs” in the Antarctic winter?

 

I    Cl2              III  CF2Cl2

II  HOCl          IV  ClONO2

 

(a)    I and II

(b)   I and III

(c)    I and IV

(d)   II and IV

(e)    I, II, and IV

(f)     all

(g)    none

 

Part Two:  Problems

 

If you can’t answer a part, guess and use your guess in the next part!!!

 

7.                  The amount of CH4 emitted annually is estimated to be 25 to 50 times greater than the amount of N2O emitted annually, yet the atmospheric concentration of CH4 is estimate to be only 6 times higher.  Explain.

 

Methane can undergo rapid oxidation by OH radicals in the troposphere.  Nitrous oxide does not react in the troposphere.  It is eventually destroyed by photolysis in the stratosphere.  So it has a much longer residence time, and therefore its concentration grows faster than that of methane.

 

8.                  Choose one of these air pollutants, CO, NOx, VOCs, and particulates.  Give examples of the following information.

(a)    environmental effects

(b)   human health effects

(c)    major sources

(d)   atmospheric reactions

 

CO: a) little, b) toxic, c) incomplete combustion of fossil fuels, d) CO + OH à HOCO

 

NO: a) acid rain, b) irritant, c) heat of fossil fuel combustion, d) NO + O3 à NO2 + O2

 

VOCs: a) smog, b) irritant, c) incomplete combustion of fossil fuels, d) H2C=CH2 + OH à H2C-C(OH)H2

 

particulates: a) classic smog, b) respiratory disease, c) incomplete combustion of fossil fuels, d) adsorb chemicals

 

9.                  Consider the following reaction:

 

OH + O3 à HO2 + O2

DH = -159 kJ/mol

Ea = 7 kJ/mol

 

(a)    Draw a reaction coordinate diagram.

 

 

 

 

 

 

 

 

 

 

 


(b)   Is the reaction favored or unfavored?  DH is negative, exothermic reaction, favored

 

(c)    Will the reaction occur rapidly at room temperature?  Yes, 7 kJ close to kT (2 kJ)

(d)   What factors will increase the rate of reaction?  temperature, [O3], [OH]

 

10.              Describe the accepted mechanism for the destruction of ozone in the lower stratosphere catalyzed by Cl.  Discuss two methods scientists used to prove the mechanism.

 

Cl + O3 à ClO + O2

ClO + ClO à ClOOCl à 2 Cl + O2

 

Spectroscopy:  measure [ClO] and [O3]

Measure rate constants for reactions, model with computer