GENERAL CHEMISTRY II
CHEM 1312.001
EXAM 3
Wednesday April 8, 1998


Note: On some problems you will need to use the universal gas constant, R. Note that its value is as follows:

R = 8.3145 J / ( K mol )

1. In a kinetic study of the reaction

     2NO(g)      +      O2(g)      ---------->      2NO2(g)

the following data were obtained:
Expt. #[NO]initial[O2]initialInitial Rate
10.0125 mol L-10.0253 mol L-10.02805 mol L-1 s-1
20.0250 mol L-10.0253 mol L-10.11220 mol L-1 s-1
30.0125 mol L-10.0506 mol L-10.05610 mol L-1 s-1
What is the order of the reaction with respect to NO?

    a) 0     b) 1     c) 2     d) 3    e) 4

2. Referring to the reaction and data in problem 1, what is the order of the reaction with respect to O2?

    a) 0     b) 1     c) 2     d) 3     e) 4

3. Referring to the reaction and data in problem 1, what is the numerical value of the rate constant?

    a) 89     b) 177     c) 1753     d) 3506     e) 7096

4. Referring to the reaction and data in problem 1, what are the units of the rate constant?

    a) s-1     b) mol L-1 s-1     c) mol-2 L2 s-1     d) mol2 L-2 s-1     e) mol2 L2 s-1

5. Referring to the reaction in problem 1, is it an elementary reaction?

    a) Definitely YES     b) Definitely NO     c) Can't tell

6. Cyclobutane, C4H8 decomposes to give to give ethylene, C2H4. The reaction is first order and is represented by the equation

     C4H8(g)      ---------->      2C2H4(g)

An experiment was conducted in which C4H8, at an initial concentration of 1.50 x 10-3 M was allowed to decompose by the above reaction. At the temperature of the experiment, the reaction had a rate constant of 5.09 x 10-4 s-1. What was the concentration of C4H8 2.50 hours after the start of the reaction?

    a) 8.13 x 10-7 M     b) 5.21 x 10-6 M     c) 1.54 x 10-5 M

    d) 7.16 x 10-4 M     e) 1.05 x 10-3 M

7. Is the reaction in problem 6 elementary?

    a) Definitely YES     b) Definitely NO     c) Can't tell

8. The decomposition of dinitrogen pentoxide, N2O5 is first order. The reaction is

     2N2O5(g)      ---------->      4NO2(g)      +      O2(g)

An experiment was conducted in which the initial concentration of N2O5 was 1.18 x 10-3 M. At the temperature of the experiment, the reaction has a rate constant of 1.03 x 10-5 s-1. What was the half life of the reaction?

    a) 1.83 x 103 s     b) 6.73 x 104 s     c) 4.14 x 105 s

    d) 7.19 x 106 s     e) 8.23 x 107 s

9. Is the reaction in problem 8 elementary?

    a) Definitely YES     b) Definitely NO     c) Can't tell

10. Ethyl chloride, C2H5Cl, decomposes to give ethylene, C2H4, and hydrogen chloride, HCl. The reaction is first order.

     C2H5Cl(g)      ---------->      C2H4(g)      +      HCl(g)

An experiment was conducted in which the initial concentration of C2H5Cl was 1.00 x 10-3 M. At the temperature of the experiment, the reaction had a rate constant of 2.58 x 10-3 s-1. How long would it take for the concentration of C2H5Cl to be reduced to one fourth ( 1/4 ) of its original value?

    a) 269 s     b) 537 s     c) 806 s     d) 1516 s     e) 1940 s

11. Is the reaction in problem 10 elementary?

    a) Definitely YES     b) Definitely NO     c) Can't tell

12. If a reaction has a rate constant of 1.17 x 10-3 s-1 at 30 oC and 2.30 x 10-3 s-1 at 50 oC, what is the activation energy of the reaction?

    a) 7.41 kJ / mol     b) 14.7 kJ / mol     c) 27.5 kJ / mol

    d) 39.4 kJ / mol     e) 51.6 kJ / mol

13. If the rate of a chemical reaction triples when the temperature is raised from 25 oC to 35 oC, what is the activation energy of the reaction?

    a) 15.9 kJ / mol     b) 25.7 kJ / mol     c) 58.6 kJ / mol

    d) 68.5 kJ / mol     e) 83.9 kJ / mol

14. If a chemical reaction has a rate constant of 7.15 x 10-3 s-1 at 20 oC and an activation energy of 50.0 kJ / mol, what is the rate constant at 40 oC?

    a) 0.0265 s-1     b) 0.0913 s-1     c) 0.1433 s-1     d) 0.2511 s-1     e) 0.3619 s-1

15. The decomposition of hydrogen iodide (HI) is second order. The reaction is

     2HI(g)      ---------->      H2(g)      +      I2(g)

An experiment was conducted in which the initial concentration of HI was 9.80 x 10-3 mol L-1. At the temperature of the experiment, the reaction had a rate constant of 0.248 mol-1 L s-1. What is the half life of the reaction?

    a) 3 s     b) 15 s     c) 85 s     d) 226 s     e) 411 s

16. Is the reaction in problem 15 elementary?

    a) Definitely YES     b) Definitely NO     c) Can't tell

17. The half life of a reaction does not depend on the concentration (ie, remains constant as the reaction proceeds) if the reaction is

    a) first order     b) second order     c) elementary

    d) both a and b     e) none of these

Answers:

1 c      2 b      3 e      4 c      5 c     

6 c      7 c      8 b      9 b      10 b     

11 c      12 c      13 e      14 a      15 e     

16 c      17 a



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