Exam 1A, Spring 2018

1. Give the chemical formula for the sulfite ion.

2. Give the name for Cr2O72–.

3. What are the units of rate of 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+] = 0.25 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 0.010 0.025 2.4×10–6


2 0.0050 0.025 1.2×10–6


3 0.010 0.0125 6.0×10–7


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