CHEM 1215 Unit 3 Practice Problems

 

1.    Given the following equation and data, write the rate law equation, including the value of the rate constant.  (Make sure you include the correct units for the rate constant.)  What is the overall order of the reaction?  4 NO (g)  +  O2 (g)  à  2 N2O3

 

Expt.

[NO] (M)

[O2] (M)

Initial rate (M/s)

1

0.012

0.020

0.102

2

0.018

0.020

0.2295

3

0.018

0.040

0.459

 

 

2.    Calculate the average reaction rate for the disappearance of reactant A in the time interval from 20 min. to 50 min. using the following data.    

 

A à 2 B

 

Time (min)

[A] (M)

0.0

1.00

10.0

0.74

20.0

0.54

30.0

0.40

40.0

0.30

50.0

0.22

 

 

3.    Using the information from the previous question, calculate the concentration of B present after 40.0 minutes.  (Hint:  Is this a kinetics question??)

 

4.    Chlorine and water vapor react to form hydrogen chloride and oxygen.  A mixture of 0.25 M chlorine and 0.25 M water vapor is allowed to react.  After 5 hours at a particular temperature, the mixture contains 0.24 M hydrogen chloride.  Calculate the concentration of chlorine present in the mixture after 5 hours at that temperature.

 

5.    Nitrogen monoxide decomposes to form nitrogen dioxide and dinitrogen monoxide.  Write an expression that relates the rate of disappearance of nitrogen monoxide with the rate of appearance of dinitrogen monoxide in this reaction.

 

6.    Using the equation from question 5, calculate the rate of appearance of dinitrogen monoxide when the rate of disappearance of nitrogen monoxide is 1.6 x 10-3 M/s.

 

7.    Iodine-131 is often used to study the function of the thyroid gland.  If iodine-131 decomposes via a first order reaction and has a half life of 8.1 days, how much would be left of a 0.50 g sample after 40.5 days?

 

8.    How long (in days) would it take for 90.0% of a 2.00 g sample of iodine-131 to decompose if it decomposes via a first order reaction with a half life of 8.1 days?

 

9.    A certain pesticide has a half life of 0.478 yr and decomposes via a first order reaction.  What is the concentration of a solution of the pesticide after 2.50 years if its original concentration is 5.25 x 10-3 M .

 

10.  Use the following data to determine if the decomposition of N2O5 is zero order, first order, or second order with respect to N2O5.  Write the rate law for this decomposition reaction, including the value of the rate constant.

 

Time (min)                  [N2O5]

0.                                 0.0165

10.                               0.0124

20.                               0.0093

30.                               0.0071

40.                               0.0053

50.                               0.0039

60.                               0.0029

 

11.  Draw a reaction energy diagram for an endothermic reaction with an activation energy of 15 kJ/mol and a heat of reaction of 3 kJ/mol.  Label the reactants, products, transition state on the diagram and show the activation energy and heat of reaction.

 

12.  The decompositon of hydrogen iodide to form hydrogen and iodine has rate constants of 9.51 x 10-9L/mol.s at 227oC and 1.10 x 10-5 L/mol.s at 327oC.

 

a.    Calculate the activation energy for the reaction.

b.    Calculate the value of A.

c.    Calculate the rate constant for the reaction at 277 K.

 

13.  I would suggest that you re-work questions 1, 2, 13, 17, 18, 24, and 29 of the Unit 2 practice problems.