Hour Test 3 (canary)                        Name__________________________

CHM 1045 (Dr. Light)                     Soc.Sec.Num._____________________

April 12, 1996                   8:00 am         Recitation Section_______

PLEASE NOTE:    The final exam in this course is a
                block exam scheduled from 3-5 on
                Wednesday, April 24, in this room. 
                This is not the regularly scheduled
                time for an 8:00 MWF class.

This exam consists of 4 pages.  Make sure you have
one of each.  A fifth page has some data you may need
for some of the problems.  You may tear it off and
use it as scratch paper.

Be sure to read all instructions carefully.  If
anything is not clear, raise your hand and ask!

Points

(10)1.Draw two resonance structures for the each of the following
     molecules or ions, and indicate the formal charge on each atom in
     each structure:

     O3                              NO2-1










(7)2.There are two bonds between carbons and four C-H bonds in the
     compound ethylene (C2H4).  Identify each bond by its type
     (indicated by a Greek letter), and by the type of atomic orbital
     from each atom used in forming the bond.

     Bond       Bond type            C atomic orbital(s)   H atomic orbital

     C-C

     C-C

     C-H


(5)3.Draw two resonance structures for OCN-1 (carbon is the central
     atom).  Circle the structure which you believe is the better of the
     two, and explain why.
(15)4.For each of the following compounds or ions, draw the best Lewis
     dot structure.  (If more than one resonance structure is "best",
     draw only one).  The central atom is underlined.  Give the electron
     pair geometry, the molecular geometry, and the hybridization about
     the central atom.


CompoundLewis Structure    electron pair   molecular       hybridization
                             geometry       geometry


BCl3









BrF5









ClO3-









(10)5.Give the molecular geometry of each of the following molecules,
     sketch a picture of the structure, use an arrow to indicate the
     polarity of each bond, and indicate whether the molecule as a whole
     would be polar or non-polar.

     CCl4                                  SO2


(16)6.Calculate þH for the following reactions using the table of bond
     energies on the last page.

     (a)   HCN     +     3 H2    ----->     CH4      +       NH3














     (b)   4 CH4  +  O2    ---->    2 C2H6    +     2 H2O   















(13)7.The Nickel-Cadmium battery generates electricity by the following
     chemical reaction.  Calculate the oxidation number of every atom in
     each reactant and product, and place the value in the blanks below
     the molecule.  Then indicate what atoms are being reduced and what
     atoms are being oxidized during the reaction.

     Cd(s)  +   2 H2O   +   NiO2(s)  ---->  Cd(OH)2(s)  +   Ni(OH)2(s)

     Cd ____     H ____     Ni ____        Cd ____         Ni ____

                 O ____      O ____         O ____          O ____

                                            H ____          H ____



Atom(s) oxidized in the reaction _______


Atom(s) reduced in the reaction ________


(8)8.A tank containing 3.5 moles of nitrogen gas and 2.4 moles of helium
     gas at 25 oC has a pressure of 7.8 atmospheres.  

     (a)   What are the partial pressures of nitrogen and helium?






     (b)   What would the total pressure in the tank be if an additional
           1.2 moles of nitrogen were added to the tank, and the
           temperature were raised to 55 oC?







(8)9.What volume of oxygen, measured at 273 K and 1.00 atm pressure,
     must be used to completely burn 66.0 grams of C2H6.?  (Write the
     balanced equation for the reaction).
















(8)10.The empirical formula for cyclohexane is CH2.  If 2.7 g of
     cyclohexane has a volume of 1.00 L at 0.984 atm and 95.0oC,
     determine the molecular formula of cyclohexane.  (Show your work).










The following data may be of use to you in answering some of the
questions.  
R = 0.08206 L-atm/mol-K;  1 atmosphere = 760 torr = 101.325 kPa

Average Bond Energies (kJ/mol)

Single Bonds:

C-H   413       N-H  391        O-H  463        F-F   155
C-C   348       N-N  163        O-O  146        
C-N   293       N-O  201        O-F  190        Cl-F  253
C-O   358       N-F  272        O-Cl 203        Cl-Cl 242
C-F   485       N-Cl 200        O-I  234   
C-Cl  328       N-Br 243                        Br-F  237
C-Br  276                       S-H  339        Br-Cl 218
C-I   240       H-H  436        S-F  327        Br-Br 193
C-S   259       H-F  567        S-Cl 253        
                H-Cl 431        S-Br 218        I-Cl  208
Si-H  323       H-Br 366        S-S  266        I-Br  175
Si-Si 226       H-I  299                        I-I   151
Si-C  301
Si-O  368


Multiple Bonds:

C=C   614       N=N  418        O2   495
CðC   839       NðN  941
C=N   615                       S=O  523
CðN   891                       S=S  418
C=O   799
CðO  1072

Some Electronegativities

H  2.1      (2A)      (3A)       (4A)       (5A)      (6A)       (7A)
Li 1.0     Be 1.5    B  2.0     C  2.5     N  3.0    O  3.5     F  4.0
Na 0.9     Mg 1.2    Al 1.5     Si 1.8     P  2.1    S  2.5     Cl 3.0
K  0.8     Ca 1.0    Ga 1.6     Ge 1.8     As 2.0    Se 2.4     Br 2.8
           [Transition Metals 1.0-2.4]
Rb 0.8                                               Te 2.1     I  2.5
Cs 0.7                                               Po 2.0     At 2.2