Exam 1B, Spring 2018

1. Give the chemical formula for the nitrite ion.

2. Give the name for CrO42–.

3. What are the units of the rate constant of a second order reaction?

4. The rate law for the reaction shown below is first order in each reactant with k = 3.0×10–4 M–1s–1 at 25 °C. Calculate the rate of reaction at 25 °C if [NH4+] = 0.50 M and [NO2–] = 0.050 M.

NH4+(aq) + NO2–(aq) → N2(g) + 2 H2O(l)

5. Consider the first order reaction: PH3(g) → P4(g) + H2(g).

a. Balance the reaction.

b. The half-life is 35.0 s at 680 °C. Find the rate constant, including units.

6. The mechanism shown below is proposed for the reaction Tl+(aq) + Ce4+(aq) → Tl3+(aq) + Ce3+(aq) that occurs only in the presence of Mn2+(aq) with a rate law of Rate = k[Ce4+][Mn2+].

a. Is the mechanism plausible? Why or why not?

b. What is the role of the Mn2+?

Ce4+(aq) + Mn2+(aq) → Ce3+(aq) + Mn3+(aq)

Ce4+(aq) + Mn3+(aq) → Ce3+(aq) + Mn4+(aq)

Tl+(aq) + Mn4+(aq) → Tl3+(aq) + Mn2+(aq)

7. Find the rate law and average rate constant (including units) for the reaction run at 700 °C: 2 H2(g) + 2 NO(g) → 2 H2O(g) + N2(g)

Experiment [H2] (M) [NO] (M) Initial Rate (M·s–1)


1 0.020 0.025 4.8×10–6


2 0.010 0.025 2.4×10–6


3 0.020 0.0125 1.2×10–6


8. The rate constant for the reaction 2 N2O5(g) → 2 N2O2(g) + O2(g) was measured at several temperatures, as given below. Plot (using best practices for graphing) the data so that you could find the activation energy. A correct plot will have a slope of –12143; find the activation energy in units of kJ/mol. What is the order of reaction?

T °C k (s–1)


0 7.87×103


25 3.46×105


45 4.98×106


65 4.87×107


Answers