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 law.)  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.

 

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.      Write an expression that relates the rate of disappearance of Br2 (g) with the rate of appearance of NOBr (g) in the following reaction.

2 NO (g) + Br2 (g) à 2 NOBr (g)

 

 

4.      Using the equation from question 3, calculate the rate of disappearance of bromine when the rate of appearance of NOBr is 1.6 x 10-3 M/s.

 

5.      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?

 

6.      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 .

 

7.      Use the following data to determine if the decomposition of N2O5 is first order or second order with respect to N2O5.

 

Time (min)                  [N2O5]

0                                  0.0165

10                                0.0124

20                                0.0093

30                                0.0071

40                                0.0053

50                                0.0039

60                                0.0029

 

8.      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.

 

 

9.      The decompositon of hydrogen iodide to form hydrogen and iodine has rate constants of 9.51 x 10-9L/mol.s at 500. K and 1.10 x 10-5 L/mol.s at 600. K.

 

a.      Calculate the activation energy for the reaction.

b.      Calculate the value of A.

c.      Calculate the rate constant for the reaction at 550. K.