New Approaches for Teaching the Chemical Principles of Engineering Phil Westmoreland University of M

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New Approaches for Teaching the Chemical
Principles of EngineeringPhil
WestmorelandUniversity of Massachusetts
Amherstwestm_at_ecs.umass.edu
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What 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!

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ChE 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

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Yes, 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.

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We 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.

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1. 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
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2. Property correlations require a grasp of
underlying principles.
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3. Molecular visualization helps develop this
grasp.
Compare the descriptions (C33N3H43)FeCl2, a
liganded di(methyl imide xylenyl) aniline ...
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See functionality with the 3-D structure.
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A key tool for describing molecular biology
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Such as enzymatic docking.
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5. 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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6. 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.

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Example 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.).

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Then 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.

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Get 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.

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For 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

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H-atom eigenfunctions y correspond to hydrogenic
atomic orbitals.
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Construct 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

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Simulate 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)

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Then explain Hartree-Fock, density functional
theory, compound methods, and then...
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7. 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.

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Safety / reactor engineering example
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Simplest properties are interaction energies
Here, the van der Waals well for an Ar dimer.
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In 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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