Chemistry 3202 - Unit 2 Assignment 1
1.
3 marks. In your own words, describe how collision theory explains the factors that affect a
reaction rate.
2. 4 marks. Suppose that you have a solid sample of an organic substance. You are going to burn
the substance in an analytical substance and determine whether or not any unburned matter
remains. The substance is somewhat hard, and you receive it in a solid chunk.
a. Suggest two ways to increase the rate of burning so that your analysis will take less
time.
b. Explain why your suggestions would work, using the theories you learned in this section.
3. 5 marks. Consider the following reaction:
2AB

A2 + B2
Ea fwd = 75 KJ
E a rev = 143 KJ
a. Is the reaction endothermic or exothermic in the forward direction?
b. Draw and label a potential energy diagram, Including the enthalpy change.
c. Suggest a possible activated complex.
4.
3 marks. Using a diagram, show why one exothermic reaction may be slower than another
exothermic reaction.
5.
3 marks. What is the difference between an elementary reaction and an overall reaction?
6.
3 marks. Why are reaction intermediates only ‘proposed?’
7.
3 marks. What is the difference between a reaction intermediate and an activated complex?
8. 4 marks. Consider the reaction below:
i. D + E  A2B2
ii. A2B2 + C  AB2C + A
iii. AB2C  AB2 + C
iv. AB2  A + B2
a. What is the role of AB2C and AB2?
b. What is the role of C?
c. How can you tell the difference between a reaction intermediate and a catalyst if give the
reaction mechanism?
9.
4 marks. Chlorine gas reacts with aqueous hydrogen sulfide (also known as hydrosulfuric acid)
to form elemental sulfur and hydrochloric acid. The mechanism below is proposed
Step 1: Cl2 + H2S  Cl+ + HCl + HS-
(slow)
Step 2: Cl+ + HS-  HCl + S
(fast)
Sketch a potential energy diagram for this reaction, with labels to identify activation energy, transition
state, rate-determining step, and any reaction intermediate.
10. 5 marks. The decomposition of hydrogen peroxide, H2O2, may be catalyzed with the iodide ion.
Chemists propose this reaction occurs according to the following mechanism:
Step 1: H2O2 + I-  H2O + OI-
(slow, rate determining)
Step 2: H2O2 + OI-  H2O + O2 + I-
(fast)
a. Show that these two steps are consistent with the overall stoichiometry of the reaction.
b. How does this mechanism account for the fact that the iodide ion is a catalyst?
c. Draw and label a potential energy diagram for this mechanism, including the rate
determining step, the catalyst and reaction intermediates.
d. What effect would decreasing the concentration of hydrogen peroxide have on the overall
rate?
11. 3 marks. Research an enzyme used in the human body. Describe the function of the enzyme,
and write the reaction that the enzyme catalyzes. What would be the health effects on the
human body if this enzyme was not produced by the human body?