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11.12 - Lewis-Randall Rule and Henry's Law
Book navigation
- Chapter 1 - Basic concepts
- Chapter 2 - The energy balance
- Chapter 3 - Energy balances for composite systems.
- Chapter 4 - Entropy
- Chapter 5 - Thermodynamics of Processes
- Chapter 6 - Classical Thermodynamics - Generalization to any Fluid
- Chapter 7 - Engineering Equations of State for PVT Properties
- Chapter 8 - Departure functions
- Chapter 9 - Phase Equlibrium in a Pure Fluid
- Chapter 10 - Introduction to Multicomponent Systems
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Chapter 11 - An Introduction to Activity Models
- 11.01 Modified Raoult's Law and Excess Gibbs Energy
- 11.02 - Calculations with Activity Coefficients
- 11.05 - Modified Raoult's Law and Excess Gibbs Energy
- 11.06 - Redlich-Kister and the Two-parameter Margules Models
- 11.07 - Activity Models at Special Compositions
- 11.08 - Preliminary Indications of VLLE
- 11.09 - Fitting Activity Coefficients to Multiple Data
- 11.12 - Lewis-Randall Rule and Henry's Law
- 11.13 - Osmotic Pressure
- Chapter 12 - Van der Waals Activity Models
- Chapter 13 - Local Composition Activity Models
- Chapter 14 - Liquid-liquid and solid-liquid equilibria
- Chapter 16 - Advanced Phase Diagrams
- Chapter 15 - Phase Equilibria in Mixtures by an Equation of State
- Chapter 17 - Reaction Equilibria
- Chapter 18 - Electrolyte Solutions
Henry's Law (10:16)
Introduction to Henry's Law (10:16) (msu.edu)
Fugacities are calculated relative to standard state values, and the relations developed earlier in the chapter use a pure fluid standard state. What if the pure fluid does not exist as a liquid when pure? One choice is to use Henry's law.
HenrysLaw:Estimation&Validation
Henry's Law can be used to compute VLE of gases in solvents. We can estimate Henry's "constants" (uakron.edu, 12min) by Eqns. 11.64 and 11.68. Here we demonstrate the procedure for CO2+toluene and CO2+water. In some cases, the estimates can be good and in some cases they can be quite bad. The only way to know for sure is to validate your model with experimental data. Validation essentially involves finding data in the library and plotting on the same graph as the predictions. You should also compute the average deviations to provide a numerical measure of the goodness of fit.
Comprehension Questions:
1. Does the SCVP+ model predict higher or lower pure component fugacities than SCVP?
2. Why is it unusual for the deviations from Henry's Law to be positive?
3. Find experimental data for supercritical CO2+acetone. Identify the optimal value of A12 in the SCVP+M1 model to fit these data and compute the root mean square deviation (rmsd) of pressure: rmsd = sqrt(sum(Pcalc-Pexpt)^2).
4. Repeat 3 for N2+acetone. Compare the SCVP, SCVP+, and SCVP+MAB predictions as well as including experimental data.
Beyond Henry's Law
Characterizing gas solubility beyond Henry's Law concentrations (uakron.edu, 6min) This presentation shows how to use the M2 model to fit the gas solubility when the pressure deviates from the linear behavior indicated by Henry's Law. It is very similar to the procedure illustrated in Section 11.9, but we use a slightly customized format here.
Comprehension questions:
1. Find experimental data for supercritical CO2+acetone. Identify the optimal value of A12 and A21 in the SCVP+M2 model to fit these data and compute the root mean square deviation (rmsd) of pressure: rmsd = sqrt(sum(Pcalc-Pexpt)^2/NPTS). Also tabulate the %AAD for this system.
2. Repeat 1 for ethylene+water at 100F. (Hint: cf. DECHEMA for reference to Anthony and McKetta, 1967)