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New Approaches for Teaching the Chemical Principles of Engineering Phil Westmoreland University of Massachusetts Amherst westm@ecs.umass.edu. What are the chemical principles of engineering?.

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New Approaches for Teaching the Chemical Principles of EngineeringPhil WestmorelandUniversity of Massachusetts Amherstwestm@ecs.umass.edu

what are the chemical principles of engineering
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 don’t care! These are all “molecular sciences”.
  • Student need to master these principles - and can.
  • Molecular modeling and computer visualization helps greatly!
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

ChE is the engineering profession that focuses on applying chemistry.
yes che is the engineering profession that focuses on applying chemistry
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.
we all need to understand the chemical principles of engineering because we all need properties
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.
1 most property predictions are by correlations wholly empirical or theory based
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

3 molecular visualization helps develop this grasp
3. Molecular visualization helps develop this grasp.

Compare the descriptions:

(C33N3H43)FeCl2,

a liganded di(methyl imide xylenyl) aniline ...

5 for getting and using quantitative correlations properly use the appropriate theory

Continuum Mechanics

Statistical Mechanics

Quantum Mechanics

5. For getting and using quantitative correlations properly, use the appropriate theory.

1 m

100 m

0.1 m

10 nm

Length

1 nm

10 ns

1 hr

1 ps

Time

(After Maroudas, 2002)

6 we can use these computational tools to help us teach about theory and applications
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.
example sketch ethylene calculate optimized structure frequencies thermo compare to data
Example: Sketch ethylene; Calculate optimized structure/frequencies/thermo; Compare to data.

Calculations and graphics at HF/3-21G* with MacSpartan Plus (Wavefunction Inc.).

Electron

density

HOMO;

LUMO

then they ll tackle how the needed theory
Then they’ll 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.]
get bond lengths bond angles frequencies from analogies or from quantum chemistry
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 CH4in vacuo.
  • Most simply, the goal of electronic structure calculations is energy.
  • However, usually we want energy of an optimized structure and the energy’s variation with structure.
for quantum mechanics a hamiltonian operator is used for translational kinetic energy
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
construct each mo y i by lcao
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:
simulate the real functionality with gaussians
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 r=0
    • However, all analytical integrals
  • Linear combinations of gaussians; e.g., STO-3G
    • 3 Gaussian “primitives” to simulate a STO
    • (“Minimal basis set”)
7 use them to solve some small real problems that reinforce the point
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 C2H4+OH.
  • Heat of solvation for small molecules in various solvents.
  • Fit Lennard-Jones parameters for simple potential.
slide26

"Chemistry and life sciences in a new vision of chemical engineering," Chemical Engineering Education, 35(4), 248-255 (2001).

http://www.et.byu.edu/~rowley/WebModules/modules.htm

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.