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Spring 2002

1. Complete and balance the following reactions.

a. HCl(aq) + NaOH(aq)

b. Ba(OH)2(s) + H2CO3(aq)

c. Ti2+(aq) + H2O(l)

d. CH3CH2NH2(aq) + H2O(l)

e. Ag+(aq) + NH3(aq)

f. Pb(NO3)2(aq) + Na2SO4(aq)

g. Hg2(NO3)2(aq) + KCl(aq)

h. C6H5COOH(aq) + H2O(l)

i. ClO3(aq) + Ag2O(s) Cl(aq) + AgO(s) (pH = 14)

j. HNO2(aq) NO2(g) + NO(g)

2. The following mechanism is proposed for a reaction:

[(P(C6H5)3)3RhCl](s) + H2(g) [(P(C6H5)3)3RhClH2](s)


[(P(C6H5)3)3RhClH2](s) + C2H4(g) [(P(C6H5)3)3Rh(CH2CH3)ClH](s)


[(P(C6H5)3)3Rh(CH2CH3)ClH](s) [(P(C6H5)3)3RhCl](s) + CH3CH3(g)


a. Write the net reaction.

b. The net reaction is an oxidation-reduction reaction. What is oxidized and what is reduced?

c. Predict the rate law.

3. The following reaction was run at 62 °C:

2 N2O5(g) 4 NO2(g) + O2(g)

The concentration of N2O5 was measured at several different times and the following plots were made:

a. What is the order of the reaction? Write the rate law.

b. Find the value of the rate constant and give the units.

4. Estimate the pH of a 0.10 M solution of Ni(NO3)2 at 25 °C. Write the appropriate chemical reactions, set up the problem and work through to the algebra stage. Then make a chemically reasonable estimate of the pH.

5. Unlike other solubility reactions, Ksp for sulfides is defined by the reaction:

MS(s) + H2O(l) M2+(aq) + HS(aq) + OH(aq)

a. Ksp for SnS could be measured using the cell Pt(s) | SnS(s) | Sn2+(aq) | S(s) || S(s) | HS(aq) | OH(aq) | Pt(s). Write the oxidation and reduction half-reactions and the net reaction.

b. Find the cell potential for the net reaction for part a. Is the reaction spontaneous or nonspontaneous? Why?

c. G° for the reaction in part a is 157 kJ/mol at 25 °C. Show how this value is obtained from the cell potential.

d. The Ksp value found from the G° value in part c is 3×10–28. Show how this value is obtained.

e. Find H° and S° for the net reaction from part a.

f. Using the data from part e gives G° = 163.2 kJ/mol and Ksp = 2.5×10–29. Compare these values to those found in part d and found in tables.

g. Show how to find molar solubility. Which Ksp value should you use? Why?

h. Will the solubility of SnS increase or decrease if the pH is increased. Explain.

i. Find the value for the equilibrium constant at 25 °C for the precipitation reaction given below. (Hint: use the Law of Multiple Equilibria and the equilibrium constants found on the first page of the exam.)

Sn2+(aq) + H2S(aq) + 2 H2O(l) SnS(s) + 2 H3O+(aq)

j. The reaction shown in part i has a single arrow. Is this justified? Why or why not?

k. Using the results of part i allows you to find G° = –28.5 kJ/mol. Show how this value is found.

l. Find H° and S° for the reaction in part i.

m. Using the thermodynamic data from part l gives G° = –44 kJ/mol. Show how this value is found. Speculate on a reason that the two values for the Gibb's energy are so different.