208 ❯ STEP 4. Review the Knowledge You Need to Score High
- B—The higher I 2 concentration will increase the
value of the rate and give a higher apparent k.
This k is higher than the true k. - A—Add the equations and cancel anything that
appears on both sides of the reaction arrows.
Total: 2 NO 2 (g) + N 2 (g) + 2 CO(g) + 2 O 2 (g) →
N 2 (g) + 2 O 2 (g) + 2 CO 2 (g) + 2 NO(g)
Leaving: 2 NO 2 (g) + 2 CO(g) →
2 CO 2 (g) + 2 NO(g)
Or: NO 2 (g) + CO(g) → CO 2 (g) + NO(g) - C—Ternary steps, steps involving three mol-
ecules, are very unlikely in mechanisms.
❯ Free-Response Question
You have 15 minutes to answer the following long question. You may use a calculator and
the tables in the back of the book.Question
2 ClO 2 + 2 OH– → ClO 3 – + ClO 2 – + H 2 O
A series of experiments were conducted to study the above reaction. The following
table provides the initial concentrations and rates.INITIAL CONCENTRATIONS (mol/L)EXPERIMENT [OH-] [ClO 2 ]INITIAL RATE OF
FORMATION OF ClO 3 -
(mol/L min)
1 0.030 0.020 0.166
2 0.060 0.020 0.331
3 0.030 0.040 0.661(a) i. Determine the order of the reaction with respect to each reactant. Make sure to
explain your reasoning.
ii. Give the rate law for the reaction.
(b) Determine the value of the rate constant, making sure to include the units.
(c) Calculate the initial rate of disappearance of ClO 2 in experiment 1.
(d) The following is the proposed mechanism for this reaction:
Step 1: ClO 2 + ClO 2 → Cl 2 O 4
Step 2: Cl 2 O 4 + OH– → ClO 3 – + HClO 2
Step 3: HClO 2 + OH– → ClO 2 – + H 2 O
Which step is the rate-determining step? Show that this mechanism is consistent with
both the rate law for the reaction and with the overall stoichiometry.