Title: New Approaches for Teaching the Chemical Principles of Engineering Phil Westmoreland University of M
1New Approaches for Teaching the Chemical
Principles of EngineeringPhil
WestmorelandUniversity of Massachusetts
Amherstwestm_at_ecs.umass.edu
2What are the chemical principles of engineering?
- Principles that underlie the useful properties of
atoms, molecules, macromolecules, continuum
ensembles, materials - Is it chemistry? Is it physics? Is it biology?
- Biochemistry? Physical chemistry? Chemical
physics? - Physical organic chemistry? Biophysical
chemistry? - Quantum mechanics? Statistical mechanics?
- Semiconductor physics? Organic semiconductors?
- I dont care! These are all molecular
sciences. - Student need to master these principles - and
can. - Molecular modeling and computer visualization
helps greatly!
3ChE is the engineering profession that focuses
on applying chemistry.
- Phase and reaction equilibria
- Bond and interaction energies
- Ideal-gas thermochemistry
- Thermochemistry and equations of state for real
gases, liquids, solids, mixtures - Adsorption and solvation
- Reaction kinetics
- Rate constants, products
- Metabolic pathways
- Transport properties
- Interaction energies, dipole
- µ, kthermal, DAB
- Analytical information
- Spectroscopy Frequencies, UV / Vis /IR
absorptivity - GC elution times
- Mass spectrometric ionization potentials and
cross-sections, fragmentation patterns - NMR shifts
- Protein folding and misfolding, docking, ADME,
drug discovery - Mechanical properties of hard and soft condensed
matter - Electronic optical properties
4Yes, ChE is the engineering profession that
focuses on applying chemistry.
- But mechanical engineers use many properties that
are molecular in origin. - Basic thermochemistry ?fHº, Cpº, Sº
- P-V-T relations
- Strength of materials
- So do civil and environmental engineers
- Chemical and biological treatment
- Air, water, soil properties
- Effects of environment on materials
- And likewise electrical and computer engineers
- Band gap as collective HOMO-LUMO differences.
5We all need to understand the chemical principles
of engineering because we all need properties.
- Maybe accurate, precisely known numbers.
- Necessary for accurate design, costing, safety
analysis. - Cost and time for calculation may be secondary.
- Maybe just accurate trends and estimates.
- Often more valuable.
- Correlate with data to get high-accuracy
predictions. - Use to identify relationships between structure
and properties. - Enormous value for product and process
development, operations, and troubleshooting. - Great data are best, but we must understand
enough theory to predicting unmeasured properties.
61. Most property predictions are by
correlations, wholly empirical or theory-based.
- Arrhenius kinetics
- Ideal gas law
- Ideal gas mixtures (P?xiP ?Pi)
- Ideal solutions
- Activity coefficients
Ken Jolls, www.public.iastate.edu/jolls/gibbsPics
/pvtn.jpg
72. Property correlations require a grasp of
underlying principles.
83. Molecular visualization helps develop this
grasp.
Compare the descriptions (C33N3H43)FeCl2, a
liganded di(methyl imide xylenyl) aniline ...
9See functionality with the 3-D structure.
10A key tool for describing molecular biology
11Such as enzymatic docking.
125. For getting and using quantitative
correlations properly, use the appropriate theory.
1 m
100 ?m
0.1 ?m
10 nm
Length
1 nm
1 ps
10 ns
1 hr
Time
(After Maroudas, 2002)
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146. We can use these computational tools to help
us teach about theory and applications.
- The educational principle
- Easy visualization and successful predictions
motivate students to study useful underlying
theories.
15Example Sketch ethylene Calculate optimized
structure/frequencies/thermo Compare to data.
Electron density
HOMO LUMO
- Calculations and graphics at HF/3-21G with
MacSpartan Plus (Wavefunction Inc.).
16Then theyll tackle How -- the needed theory.
- Maxwell-Boltzmann and Bose-Einstein statistics.
- Ideal-gas thermochemistry for Cpº and Sº, broken
down into additive translation, rotation,
vibration - Compare with group additivity correlations.
- Can develop transition-state theory quickly,
logically.
17Get bond lengths, bond angles, frequencies from
analogies -- or from quantum chemistry.
- Efficiently explain the underlying quantum
chemistry. - Easiest to think of a small, covalently bonded
molecule like H2 or CH4 in vacuo. - Most simply, the goal of electronic structure
calculations is energy.
- However, usually we want energy of an optimized
structure and the energys variation with
structure.
18For quantum mechanics, a Hamiltonian operator is
used for translational kinetic energy.
- Obtain a Hamiltonian function for a wave using
the Hamiltonian operator
to obtain
where Y is the wavefunction, an eigenfunction
of the equation
- Born recognized that Y2 is the probability
density function
19H-atom eigenfunctions y correspond to hydrogenic
atomic orbitals.
20Construct each MO yi by LCAO.
- Lennard-Jones (1929) proposed treating molecular
orbitals as linear combinations of atomic
orbitals (LCAO)
- Linear combination of s orbital on one atom with
s or p orbital on another gives s bond
- Linear combination of p orbital on one atom with
p orbital on another gives p bond
21Simulate the real functionality with gaussians.
- Start with a function that describes hydrogenic
orbitals well.
- Slater functions are best e.g.,
- Gaussian functions are better e.g.,
- No s cusp at r0
- However, all analytical integrals
- Linear combinations of
gaussians e.g., STO-3G - 3 Gaussian primitives to simulate a STO
- (Minimal basis set)
22Then explain Hartree-Fock, density functional
theory, compound methods, and then...
237. Use them to solve some small, real problems
that reinforce the point.
- Heat of combustion for dimethyloxirane safety.
- Rate constant for simple reaction like C2H4OH.
- Heat of solvation for small molecules in various
solvents. - Fit Lennard-Jones parameters for simple potential.
24Safety / reactor engineering example
25Simplest properties are interaction energies
Here, the van der Waals well for an Ar dimer.
26In conclusion,We can use these tools effectively
to teach the chemical principles our students
will need.
- Build on students chemistry education and their
prior use of properties to solve problems. - Refresh their recognitions of molecule types
using sketching / visualization codes. - Have them predict structures and properties.
- With them motivated, build the underlying theory.
- Have them obtain properties for use.
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