Exam 1B, Spring 1999

1. Briefly, distinguish between a reaction mechanism and a reaction intermediate.

2. How does a reaction quotient differ from an equilibrium constant? Be brief.

3. For the reaction For the reaction H₂O₂(aq) + 2 Fe²⁺(aq) + 2 H⁺(aq) → 2 Fe³⁺(aq) + 2 H₂O(l) the rate law was found to be Rate = k[H₂O₂][Fe²⁺]. What is the order of reaction in each reactant?

4. Write the mass action expression for K_p for the reaction: H₂(g) + I₂(g) →← HI(g)

5. Write the mass action expression for K_c for the reaction: BaCO₃(s) →← BaO(s) + CO₂(g)

6. The following data was collected for the reaction C₆H₅N₂Cl(aq) → C₆H₅Cl(aq) + N₂(g)

t (min)[C₆H₅N₂Cl] (M)

00.0710

60.0475

120.0315

180.0207

240.0144

300.0096

Make a first order plot of the data. Is the reaction first order? Why or why not?

7. A rate law for a reaction was found to be Rate = k[NO]²[Cl₂] The following mechanism was proposed:

NO(g) + Cl₂(g) → NOCl(g) + Cl(g) Slow

NO(g) + Cl(g) → NOCl(g) Fast

a. Write the overall reaction.

b. Is this a plausible mechanism? Why or why not?

8. Consider the exothermic reaction of nitrogen with hydrogen to give ammonia at equilibrium. Which way will the reaction shift if

a. Hydrogen is added to the system?

b. The pressure is decreased?

c. The temperature is decreased?

d. Fe is added as a catalyst?

9. For some reaction, the following rate data was measured:

T (°C)k (s^–1)

4504.71×10^–3

5509.39×10^–1

a. What is the activation energy in kJ/mol?

b. What is the half-life at each temperature?

Answers