“new approaches for teaching the chemical principles of engineering.” new england section conf.,...

“New Approaches for Teaching the Chemical Principles of Engineering.” New England Section Conf., March 17-18, 2006.

New Approaches for Teaching the Chemical Principles of Engineering

Phil WestmorelandUniversity of Massachusetts Amherst

[email protected]


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


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.

• 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.

• 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


2. Property correlations require a grasp of underlying principles.


3. Molecular visualization helps develop this grasp.

Compare the descriptions:

(C33N3H43)FeCl2,

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

N

N

N

Fe

H3C

H3C

Cl

Cl

i-Pr

i-Pr

i-Pr

i-Pr


See functionality with the 3-D structure.


A key tool for describing molecular biology…


Such as enzymatic docking.

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

Length

Time

1 m

100 m

0.1 m

10 nm

1 nm

1 ps 10 ns 1 hr

Continuum Mechanics

Statistical Mechanics

Quantum Mechanics

(After Maroudas, 2002)

Electronic structure theory Molecular simulations

Wavefunction methodsDensity-functional theory

Semi-empirical MO theory

"Ab initio":

Basis sets

Molecular dynamics,molecular mechanics

Monte Carlo simulations

(Computational quantum chemistry)

Quantum MD,Car-Parrinello

Potential energyfunctions

Molecular and material structure

Statisticalmechanics

Thermochemistry, kinetics, transport, materials properties, VLE, solutions


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.

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

Electrondensity HOMO;

LUMO


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.]

S=Nκ 1+lnq(V,T)

N⎛ ⎝

⎞ ⎠

+T∂ lnq(V,T)

∂T⎛ ⎝

⎞ ⎠

V

⎡

⎣ ⎢ ⎤

⎦ ⎥

S(molar)=R⋅ ln qtransqrotqvibrqelece( )+T∂ lnqtransqrotqvibrqelec

∂T⎛ ⎝

⎞ ⎠ V

⎡

⎣ ⎢ ⎤

⎦ ⎥

=Strans+Srot +Svibr +Selec


Energy E[from

EΨ=HΨ]

Position r

x

x

x

With energies,we can optimize

molecular structure

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 energy’s variation with structure.


For quantum mechanics, a Hamiltonian operator is used for translational + kinetic energy.

• Obtain a Hamiltonian function for a wave using the Hamiltonian operator:

H =−

h2

8πm∇2 +U(x,y,z)

to obtain:

where Ψ is the “wavefunction,” an eigenfunction of the equation

EΨ =H Ψ(

v q ,t){ }=

ih2π

∂Ψ(v q ,t)

∂t

• Born recognized that Ψ2 is the probability density function


H-atom eigenfunctions correspond to hydrogenic atomic orbitals.

m=0

2pz2py2px

1s

z

y

x

2s

3s 3px 3py 3pz 3d orbitals (5)

n=1

n=3

n=2

l=0 l=1 l=2

m=0 m=-1 m=+1 m=-2,-1,0,1,2


Construct each MO i by LCAO.

• Lennard-Jones (1929) proposed treating molecular orbitals as linear combinations of atomic orbitals (LCAO):

• Linear combination of p orbital on one atom with p orbital on another gives bond:

ψ i = Cμiφii=1

∞

∑

• Linear combination of s orbital on one atom with s or p orbital on another gives bond:


Simulate the real functionality with gaussians.

• Start with a function that describes hydrogenic orbitals well.

φ1s(

r r ;ζ1) =

ζ13

πexp(−ζ1

r r )

gs

r r ;α( )=

2απ

⎛ ⎝

⎞ ⎠

3/ 4

exp(−αr r 2)

r

True STO

3 gaussianfunctions

– 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”)


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

Improved electron correlation → H-F MP2 MP4 QCID(T) ... Full CI

Morecoletebaiet↓

TO-3G

3-21G

6-31G(d)

6-311G(d,)

6-311+G(d,)

Infinite bai et

Exactolution


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.


Safety / reactor engineering example:


Simplest properties are interaction energies: Here, the van der Waals well for an Ar dimer.

-150.00

-100.00

-50.00

0.00

50.00

100.00

0 2 4 6 8 10

Ar-Ar, angstroms

e/κ,Κ

HF

2MP

3MP

4MP D

4MP DQ

4MP SDQ

CCSD

( )CCSD T

- 12-6L J-0.2 / = -0.8 /kcal mol kJ mol

:Basis set- - ;aug cc pVDZ

:Method


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.

"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

“new approaches for teaching the chemical principles of engineering.” new england section conf.,...

Documents

new approaches

new england section

chemical physics

engineering profession

unmeasured properties

useful properties of

biophysical chemistry

physical organic chemistry