April 23, 2001

CHEMISTRY 105(400)

Instructor: Dusan Ristic-Petrovic

FINAL EXAMINATION

Weight: 35%

 

Name: ________________________                                I.D. # _________________                                                    

 

 

Signature: ______________________

 

Time for writing: 3 hours

 

READ ALL OF THE QUESTIONS CAREFULLY.

SHOW ALL OF YOUR REASONING TO OBTAIN FULL MARKS

 

Question                       Value                                       Score

 

1.                                    5                                           _____

 

2.                                    7                                           _____

 

3.                                    8                                           _____

 

4.                                    4                                           _____

 

5.                                    5                                           _____

 

6.                                    8                                           _____

 

7.                                    7                                           _____

 

8.                                   12                                          _____

 

9.                                    4                                           _____                           

 

10.                                  7                                           _____

 

11.                                  6                                           _____

 

12.                                  6                                           _____

 

13.                                  6                                           _____

 

14.                                  5                                           _____

 

 

Total                            90                                        _______

 

Bonus                          (2)                                        _______

 

 

[5]        1. For the combustion reaction      

 

 

                        CH4(g)    +    2O2(g)    ¾¾®    CO2(g)    +   2H2O(l)

 

 

 

 

 

            a)  Calculate DGo and DHo at 298K

 

 

 

 

 

 

           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

            b)  How much heat would be evolved if:

                  i)   No useful work was done by the combustion reaction?

                  ii) The maximum amount of useful work was done?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[7]        2.  The activation energy for the decomposition of ammonia gas into N2 gas and H2 gas is decreased from 350 to 162 kJ/mol in the presence of a tungsten catalyst.

 

a)      By what factor will the reaction rate be increased by the tungsten catalyst

at 700.oC?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

b)      According to collision theory, what does the capital “A” in the Arrhenius

      equation represent?

 

 

 

 

 

 

 

 

c)      Which of the following changes will affect the numerical value for the rate constant kobs? Circle your choice(s).

 

 

i)                    an increase in temperature

 

 

ii)                   a doubling of the reactant concentration

 

 

iii)                 the addition of a catalyst

 

iv)        changing the solvent from water to an organic solvent

 

[8].       3.  Provide a sketch for the galvanic cell

 

 

Sn/Sn2+(aq)(1.00 M)//Cr2O72-(aq) (1.00 M), H+(aq)(1.00 M), Cr3+(aq) (1.00 M)/Pt

 

 

a)      Give the overall cell reaction, identify the anode and the cathode and calculate the cell voltage at standard conditions.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question # 3 Continued

 

 

b)      Calculate DGo and Keq for the cell reaction at 25oC.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

c)      Calculate the cell potential at 25oC if the concentrations of all of the

dissolved metal ions are kept the same but the pH in the cathodic

compartment is increased from 0.000 to 3.000.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

            [4]  4.  a)   Given the following standard reduction potentials, show that UO2+

                  will spontaneously disproportionate in acidic solution at standard

                  conditions:

 

           


           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                  b)   Is UO2+ a better oxidizing agent or reducing agent?  Justify your answer.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[5]        5.  The standard enthalpy of formation for HCN(g) (i.e DHof HCN(g)) is

                 135.1 kJ/mol. By using this piece of information along with the appropriate

                 thermodynamic data from the data sheet, calculate the bond energy for the CN 

                 bond in HCN. (Note: Each HCN molecule is held together by one CN bond

                 and one CH bond, i.e. the connectivity is H-C-N)

                 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[8]        6.  The half-life for the second order decomposition…

           

 

 

 


                 is 32.0 minutes when the initial concentration of A is 0.280 M.

 

 

a)      Write down the differential rate law for the reaction.

 

 

 

 

b)      How many minutes would it take for the concentration of A to drop

from 0.280 M to 0.0122 M?

 

 

 

 

 

 

 

 

 

 

 

c)      Calculate the concentration for both A and B at t = 200.0 minutes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

d)      Estimate the instantaneous  rate of reaction at t = 200.0 minutes.

 

 

 

 

 

 

 

 [7]       7.  Molecular chlorine can be prepared by reacting molecular oxygen with

                 hydrogen chloride gas:

                

 

 

                        4HCl(g)    +    O2(g)   ¾¾®     2Cl2(g)    +    2H2O(g)

 

 

                        The Kp for this reaction is 1.55 x 103 atm-1 at 400 K and 

                        5.25 x 10-5 atm-1 at 800 K.

 

 

 

 

            a)  Find the DHo for the reaction without using DHof  values from the data sheet.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question # 7 Continued

 

b)      Calculate DGo and Kp for the forward reaction at 25oC. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

            c)       Determine the direction of the spontaneous reaction when:

 

                        PH2O = 1.00 atm, PCl2 = 1.00 atm

                        PO2 = 1.00 x 10-3 atm, PHCl = 1.00 x 10-3 atm and  T = 298 K.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[12]      8.  Complete the following table:

 

 

Molecular             Lewis Dot          Sketch of the          VSEPR      Molecular       Is the

Species                 Structure            Molecule (with       Notation     Shape             molecule

                                                        lone pairs)                                                         polar?

 

 

 

 

SeF4

 

 

 

 

 

 

 

 

 

 

SbCl5

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                         

PF6-

 

 

 

 

 

 

 

 

 

 

 

 

[4]        9.  a)  Draw three valid resonance structures for fulminic acid. 

                      Be sure to include all non-zero formal charges. Pick the structure(s)

                      that most accurately depict(s) the bonding in the molecule. (Note:

                      The sequence of atoms in the molecule is CNOH).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[7]        10.  The following kinetics data were obtained for the reaction…

 

                

 

 

 

 

 


             where Reaction Rate = - D[I-]/Dt

 

            [I-], M                      [Fe3+], M                Initial Rate (moles/L.sec)

 

           0.050                         0.100                        5.75 x 10-2

      

           0.100                         0.050                        0.115

 

           0.050                         0.300                        0.1725

 

 

 

 

 

 

 

a)      Determine the differential rate law and the value for k.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question # 10 Continued

 

b)      Is your empirical rate law consistent with the proposed mechanism shown

below?  Be sure to justify your answer.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


[6]        11. Complete the following short answer questions:

 

 

a)      The reaction between 1.0 M MnO4-(aq) and 1.0 M Fe2+(aq)1.0 M H+(aq) at 25oC   

 

 (spontaneous/non-spontaneous) _____________________. In this reaction, the Fe2+ ion 

 

is acting as the (oxidizing agent/reducing agent) ______________________.

 

 

 

 

            

 

     b)   Select a reagent from the table of standard reduction potentials

           that  is capable of oxidizing water and write the balanced equation for the overall

          reaction.

 

 

 

 

 

 

 

 

 

 

 

 

    c)  Can air (0.21 atm O2) oxidize copper metal to Cu2+(aq) at 25oC in a neutral

         solution that is 0.10 M in Cu2+(aq)? Justify your answer.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[6]       12. Fill in each blank with the appropriate answer.

 

 

a)   Lewis theory can be used to explain why boron trifluoride reacts vigourously with ammonia.  The Lewis acidity of boron trifluoride is caused by it being ____________________

 

 

b)      Consider the compounds:  LiCl, MgCl2, NaCl, CCl4

 

Which compound has the greatest ionic character? ______________.

 

Which compound has the weakest intermolecular  bonding? _____________.

 

 

 

c)      What intermolecular forces must be overcome to melt

 

      diamond?_____________________________________.

 

 

 

d)      Molecular nitrogen (N2) and carbon monoxide (CO) are isoelectronic and have virtually identical molar masses.  Which substance has the higher

 

melting point?  ________________.

 

 

e)      What type of solid (ionic, molecular or network covalent) is

 

ZrBr4? ______________________ Note: ZrBr4 melts at 105oC and the pure

       liquid does not conduct electricity.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[6]        13.   The empty molecular orbital diagram for CO is given below. Complete

                     the molecular orbital diagram and then answer the questions posed below.

                     Be sure to identify Atoms A and B and don’t forget to label all of the

                     molecular orbitals in the centre of the diagram.

 

i)        What is the bond order for CO in the ground state?

 

ii)   What is the total number of p-bonds in CO?

 

iii)  Classify  CO as either paramagnetic or diamagnetic. Justify your answer.

 

 

 

 


                            Atom A                                            Atom B

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[5]       14.  A researcher requires 10.0 mg of  the radioactive isotope 32P, which has a

                   half-life of 14.3 days. It is supplied as solid Na332PO4.

              

 

 

a)      What mass of  Na332PO4 should be ordered if the delivery time from the

supplier is 72 hours?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

b)      What is the initial radioactivity (i.e. the number of atoms that disintegrate

       each second) for a 10.0 mg sample of 32P?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bonus (2 Marks): The standard reduction potential for the conversion of sulfate ions

                              to sulfur dioxide in acidic solution is 0.160 V:

 

 

 

                   SO42-(aq)   +    4H+(aq) SO2(aq)    +   2H2O(l)    Eo = 0.160 V.

 

 

                   Use this information and the appropriate equation(s)/reaction(s) from the data

                   sheet to show that SO2 gas at standard conditions will be spontaneously

                   converted to sulfuric acid upon contact with any airbourne water droplets.