Title: Chemical Reaction Equilibria
1Chemical Reaction Equilibria
2Liquid-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
3K for liquids
This expression holds at high pressures, i.e.,
When P gtgt Po
at low to moderate pressures
if the equilibrium mixture is an ideal solution
4Homogeneous reactions
- only one phase
- Read and work examples 13.5, 13.6, 13.7 13.8
13.9
5Heterogeneous 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
6If 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
71st 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 -2 2 2
- If we specify T and P the intensive variables are
fixed.
8assume 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
9where the liquid-phase fugacities can be written
as
10Use this eqn
Because ethylene much more volatile than H2O
and C2H5OH
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 1.0133, we need to find T
12From the data in appendix C
- DGo (298K) 130401 J/mol
- DHo (298K) 178321 J/mol
- Calculate DA, DB, DC, DD
- And get the integral to calculate DG(T), such
that K 1.0133 exp (- DG(T)/RT) - Solve for T,
- T1151.83 K
133rd 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
14yiP 0.5x1.5 0.75 for each gas K 0.75x0.75
0.5625, we must find T that gives that value of
K From Appendix C DGo (298K) 91121 J/mol DHo
(298K) 176013 J/mol Calculate DA, DB, DC,
DD And get the integral to calculate DG(T), such
that K 0.5625 exp (- DG(T)/RT) Solve for T,
T623.97 K
15example 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 0.3955
16How much error is introduced if one assumes that
A and B form and ideal solution?
Solve for xA 0.4005