CHM 1046                    PRE-TEST  4                  July 24, 1996


     This test is take-home and open book, and
it is intended that all members of the group
contribute to completing it.  Only one copy is
to be submitted by the group, and all members
who participated should sign their names below. 
Test is due at the beginning of class on Monday,
July 29.   (You may take values of delta Gof, delta Hof,
So, and Eo from the text.  These figures will be
provided on the hour test).

         List names in alphabetical order!

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Points

1.    The following reaction is a source of pollution from
      automobile engines.  One might ask why it is not a general
      problem in the atmosphere, which consists of 80% N2 and
      20% O2.

           N2(g)  +   O2(g)  þ   2 NO(g)

      To see why this is so:
(10)  (a)  Calculate delta Go and Kp at 25oC using the
           thermochemical data in Appendix C.












(10)  (b)  Calculate delta Go and Kp at 2100oC, the approximate
           temperature of an automobile engine.


















(10)2.Using the thermochemical data from Appendix C, calculate delta
      Go and the equilibrium constant for the following reaction,
      and compare it to the Ksp given in Appendix D.

           AgCl(s)  þ   Ag+(aq)  +   Cl-(aq)















(10)3.Using the data in Appendix C and given the pressures listed,
      calculate delta G for the following reaction:

      2 N2H4(g)  +  2 NO2(g)  þ  3 N2(g)   +  4  H2O(l)

      PN2H4 = 0.015 atm;  PNO2 = 0.005 atm; PN2 = 3 atm


















(10)4.Indicate in the blank whether the following processes involve
      an increase or a decrease in entropy:

      ________  H2O(g) ---> H2O(l).

      ________  mixing 1 mole of N2 with 1 mole of O2.

      ________  heating water from 25oC to 60oC.

      ________  CaCO3(s)  --->  CaO(s)  +  O2(g)

      ________  CO2(g)  --->  CO2(aq)



5.    For the following redox reaction:

      Cr2O72-(aq)  +  H2S(g)  ---->   Cr3+(aq)   +   So(s)

(12)  (a)  Write and balance both half cell reactions in acid
           solution.  Then give the overall balanced equation.






















(12)  (b)  Calculate Eo, delta Go, and Keq at 25oC for the equation
           as written, using data from Appendix E.
           
           













(10)6.Calculate Eored for the hydrogen electrode at pH 10.0 and one
      atmosphere pressure of hydrogen.

           2 H+(aq)  +  2e  --->  H2(g)













7.    You want to chrome plate a piece of metal using a solution of
      chromium nitrate (Cr(NO)3).

(3)   (a)  Do you attach the piece of metal to the positive or the
           negative electrode?




(3)   (b)  Is this the anode or the cathode?





(10)  (e)  You carry out the electrolysis with a current of 6.0
           amperes for 2.5 hours.  How many grams of chromium will
           be deposited?