- Principles of Chemistry II: Honors
Spring 2014, Unique 51880
Homework, Week 6
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 DG˚rxn for this system.
b) Assuming DH˚f and S˚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)
DH˚f (kJ/mol) -74.81 0 -135.44 -92.31
S˚m (J/K mol) 186.26 223.07 216.40 186.91
DG˚f (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.