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

Homework, Week 6


Homework, week 6
Answer key

1.  Chloroform can be synthesized from natural gas and elemental chlorine according to the following reaction:

CH4(g) + 3 Cl2 (g) --> CHCl3(l) + 3 HCl(g)

a)  Determine Drxn for this system. 

b)  Assuming Df and m remain constant, will this reaction proceed spontaneously at 500 K?

The following data could be useful. 

CH4(g) Cl2(g) CHCl3(l) HCl(g)

Df (kJ/mol) -74.81 0 -135.44 -92.31

m (J/K mol) 186.26 223.07 216.40 186.91

Df (kJ/mol) -50.72 0 -73.66 -95.30

r (g/cm3) 0.720 0.940 1.499 1.187

2.  The protein lysozyme unfolds at a transition temperature of 75.5 ˚C with DHunfold = 509 kJ mol-1.  Calculate the entropy of unfolding of lysozyme at 25˚C, given that the difference in the constant-pressure heat capacities upon unfolding is 6.28 kJ K-1 mol-1 and is assumed to be independent of temperature.

3. The molar enthalpy of vaporization of chloroform (CHCl3) at its normal boiling point, 80.1˚C, is 30.7 kJ mol-1.  Assuming that DHvap and DSvap  remain constant, determine DGvap at 75˚C, 80.1˚C, and 85˚C.

4.  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)?

5.  The water-gas shift reaction is an important industrial source of pure H2(g) for ammonia synthesis:

CO(g) + H2O(g) --> H2(g) + CO2(g)

What would happen to the equilibrium concentration of each species if you increase the total pressure of the system by a factor of 100?

6.  Under certain conditions, water vapor dissociates into H2(g) and O2(g). At 2100 K and 1 bar, the equilibrium constant for the dissociation reaction is twice as large as at 2000 K and 1 bar.   Determine the enthalpy of the dissociation reaction, assuming it is constant over this temperature range.