CH302H - Principles of Chemistry II: Honors
Spring 2016, Unique 494200

Homework, Week 3

Homework, week 3
Answer key

1.  Most of the portable red fire extinguishers that you see in public buildings or can purchase for your home (the so-called “ABC dry chemical” extinguishers) contain powdered sodium bicarbonate that decomposes when exposed to high temperature (for example from a fire) into sodium carbonate, water, and carbon dioxide:

2 NaHCO3(s) --> Na2CO3(s) + H2O(g) + CO2(g)

a) Determine the equilibrium constant of the reaction at 150˚C.

b) At equilibrium, if the partial pressure of CO2(g) is 0.80 atm, what is the partial pressure of H2O(g)?

2.  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)

3.  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)

4.  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.