1. Chemical Reaction Equilibria
Part IV

2. Liquid-phase reactions
For a liquid phase, fio is the fugacity of pure component i at
T of the system and Po = 1 bar
fi is the fugacity of i at T and P, and fi0 is the fugacity of i at T and Po

3. K for liquids at low to moderate pressures if the equilibrium mixture
This expression holds
at high pressures, i.e.,
When P >> Po
at low to moderate pressures
if the equilibrium mixture
is an ideal solution

4. Homogeneous reactions
only one phase
Read and work examples 13.5, 13.6, 13.7; 13.8; 13.9

5. Heterogeneous reactions
more than one phase
two criteria: phase equilibrium and chemical equilibrium
Question: where the reaction takes place?
example: A(g) + B (l)  C (l)
liquid
rxn takes place in the gas phase
rxn takes place in the liquid phase
rxn takes place in both phases
gas

6. If the rxn takes place in both phases
The value of K depends on the chosen standard states
however, all methods lead to the same equilibrium
composition

7. 1st example
Ethylene reacts with water to form ethanol at 200oC and 34.5 bar; there are two phases: liquid and vapor. The pressure is kept constant. Estimate the compositions of the liquid and vapor phases.
F = 2-p + N = = 2
If we specify T and P the intensive variables are fixed.

8. assume the rxn takes place in the gas phase
C2H4(g)+H2O(g)  C2H5OH (g)
standard pressure P0 is 1 bar
calculate K at 200oC yields K =0.031
Next we need to add the VLE equations:

9. where the liquid-phase fugacities can be written as:

10. Unknowns: xH2O, xEtOH, yC2H4
Use this eqn
Because ethylene much more volatile than H2O and
C2H5OH
Unknowns: xH2O, xEtOH, yC2H4
Virial EOS for fi
Activity coeff. model or exp. Data for gi

11. 2nd example
Limestone (CaCo3) decomposes upon heating to yield quicklime (CaO) and carbon dioxide. At what temperature is the decomposition pressure of limestone =1 atm?
CaCO3 (s)  CaO (s) + CO2 (g)
Each species exists pure as an individual phase
For the solid phases, the ratio f/fo =1 (pure)
For CO2, f/fo = P/Po =1.033
So, K = P = , we need to find T

12. From the data in appendix C
DGo (298K) = J/mol
DHo (298K) = J/mol
Calculate DA, DB, DC, DD
And get the integral to calculate DG(T), such that K = = exp (- DG(T)/RT)
Solve for T,
T= K

13. 3rd example
Ammonium chloride NH4Cl(s) decomposes upon heating to yield a mixture of ammonia and hydrochloric acid. At what temperature does ammonium chloride exert a decomposition pressure of 1.5 bar?
For NH4Cl(s), DHf(298 K)=-314,430 J and
DGf(298 K)=-202,870 J.
NH4Cl(s) pure phase, f/fo =1 (pure)
The gas mixture NH3 and HCl at 1.5 bar, ideal gas mixture, for each gas the fugacity is the partial pressure yiP

14. yiP = 0.5x1.5 =0.75 for each gas
K = 0.75x0.75 = , we must find T that
gives that value of K
From Appendix C
DGo (298K) = J/mol
DHo (298K) = J/mol
Calculate DA, DB, DC, DD
And get the integral to calculate DG(T), such that K = = exp (- DG(T)/RT)
Solve for T,
T= K

15. example 4
The following isomerization reaction occurs in the liquid phase: AB, where A and B are miscible liquids for which GE/RT =0.1xAxB. If DGo (298 K)=-1,000 J, what is the equilibrium composition of the mixture at 25oC? How much error is introduced if one assumes that A and B form and ideal solution?
Solve for xA =

16. For the ideal solution:
How much error is introduced if one assumes that A and B form and ideal solution?
For the ideal solution:
Solve for xA =