CH302H - Principles of Chemistry II: Honors
Spring
2014, Unique 51880

Homework, Week 7


Homework, week 7
Answer key

1.  How do the equilibrium constants for the following two reactions compare at 25˚C:

Reaction 1:  CS2(g) + 3 O2(g) --> CO2(g) + 2 SO2(g)

Reaction 2:  1/3 CS2(g) + O2(g) --> 1/3 CO2(g) + 2/3 SO2(g)

2.  Determine the equilibrium constant for reaction 3 (K3) in terms of the equilibrium constants for reactions 1 and 2 (K1 and K2):

Reaction 1:  XeF6(g) + H2O(g) --> XeOF4(g) + 2 HF(g)

Reaction 2:  XeO4(g) + XeF6(g) --> XeOF4(g) + XeO3F2(g)

Reaction 3:  XeO4(g) + 2 HF(g) --> XeO3F2(g) + H2O(g)

3.  Phosphorous pentachloride (PCl5) decomposes into phosphorous trichloride (PCl3) and chlorine gas.  1.5 g of PCl5 is placed into a 10 mL sealed vessel and heated to 250˚C, (which is above its sublimation temperature).  Determine the partial pressure of all species at equilibrium.

4.  Dimethyl ether can be made from the dimerization of methanol:

2 CH3OH(g) --> (CH3)2O(g) + H2O(g)

Describe, both quantitatively and qualitatively, the optimum conditions of pressure and temperature to make as much of this chemical as possible.

5.  Determine which of the following molecules is a Bronsted-Lowry acid, and draw its conjugate base.

a) Cl- b) HSO4- c) NH4+

d) NH3 e) H2O f) HCN

6.  Niacin (C5H4NCOOH, also called vitamin B3) is an essential nutrient whose deficiency in the diet leads to a nasty disease called pellagra. 

a) Write a balanced equation for the equilibrium reaction of niacin with water.  This will require determining if the molecule is an acid or a base.

b) Niacin is structurally very similar to pyridine: C5H5N.  Would you predict the Ka of niacin to be greater than or less than the Ka of pyridine?  Justify your answer.

7.  The Ka of HIO3 is 0.016 at 25˚C.  Determine the pH of an aqueous solution of 0.10 M HIO3.