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

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

2. 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!

3. 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.

4. 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.

5. 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.

6. 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

7. 2. Property correlations require a grasp of underlying principles.

8. 3. Molecular visualization helps develop this grasp. Compare the descriptions: (C33N3H43)FeCl2, a liganded di(methyl imide xylenyl) aniline ...

9. See functionality with the 3-D structure.

10. A key tool for describing molecular biology…

11. Such as enzymatic docking.

12. 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)

14. 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.

15. 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

16. 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.]

17. 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.

18. 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

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

20. 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:

21. 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”)

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

23. 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.

24. Safety / reactor engineering example:

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

26. "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.