1. Chrystal D. Bruce, Erskine College
Teaching Students to Think Using Topics in Thermodynamics: The Virtual Substance Program
Chrystal D. Bruce, Erskine College
and
Carribeth Bliem and John Papanikolas, University of North Carolina at Chapel Hill
We all want our students to be intelligent, thinking individuals.
We have content to teach, but we want our students to use the content to solve problems.
What is it about Pchem, and thermo in particular, that sometimes turns students off? Math

2. Outline Virtual Substance Program Lab Assignments at Erskine
Ideal Gas Law
Real Gases
Thermodynamic Properties
Independent Projects
Student Comments
Additional Modules

3. Modeling with Virtual Substance
What is Virtual Substance?
A numerically accurate, inquiry driven, molecular dynamics software program.
Go over each box and the options; run simulation (Constant volume fixed wall)
Advantages of VS are NA, ID
Compare results with known values (Provides feedback to counteract tendency to just “generate numbers”) (Test expts)
Test theory; ID – Connection to Teaching students to think

4. Go over each box; options – script and graphics, output
Transition – What can we do with VS in Pchem specifically?

6. Virtual Substance is Numerically Accurate
Ideal Gas Law
Calculate Gas Constant, R
Measure pressure at series of volumes
Slope = RT
Argon: R = L atm/mol K
Xenon: R = L atm/mol K
Measure pressure at series of temperatures
Slope = R/Vmolar
Argon: R = L atm/mol K
Xenon: R = L atm/mol K
T = 100K
First is Boyle’s Law. Second is variation on Charles Law which relates V and T, not P and T
Obviously, many alternatives available
After this lab, they have some trust in VS. **Test’s experiments**
Virtual Substance is Numerically Accurate

7. Real Gas Behavior
NVT simulations of Argon at 165 K using periodic boundary conditions
Collect LJ, soft sphere obtain NISt calculate vdW + Hard Sphere
Pushes students to think about what makes a gas real; limitations of vdw; why density dependent?
Z = P/Pideal

8. Thermodynamic Properties
Calculate expansion coefficient, a, and isothermal compressibility, kT, for Argon behaving as an ideal gas.
Most independent. Students must determine how to design the experiment to obtain the correct data.
Left-– Must use NPT
Graphs courtesy of jessica martin.
NPT simulations
NVT simulations

9. For an Ideal Gas: Virtual Substance Error: < 2%
Format Tables/ Add exciting color
Isothermal compressibility: % error for ideal gas; 2 – 12% error for LJ data compared to NIST from earlier

10. Topic
Measurement
Kinetic Theory of Gases
Velocity Distribution
Speed Distribution
Collision Frequency
Mean Free Path
Determine average and RMS speeds from data
Real Gases
P(V)
Identify limit(s) of ideal behavior
Determine critical constants
Energy and Enthalpy
E(T)
H(T)
E(V)
H(P)
Determine CV and CP from data
Determine ∆Hvap and ∆Hfus
Internal Pressure
Combine with CP to get Joule-Thomson coefficient
Entropy
CP(T)
Calculate Sm(T)
Calculate ∆Sfus and ∆Svap
P(T)
Confirm that πT = T(∂P/∂T)V – P
Phase Diagrams
Construct phase diagram from Tfus and Tvap measurements
Phase transitions
Identification of phase boundaries
Comparison with Clausius-Clapeyron equation

11. Using Virtual Substance in Independent Projects
Submit Proposal
Revise Proposal
Conduct Research
Submit Report and Present Results to Department
Quality Clearly varied
Proposal Must include experimentally determined quantity for comparison
Funny cartoon here too – Scientific Process in action

12. Sample Student Projects
Determination of Joule-Thomson coefficient values with Virtual Substance
Calculating Internal Pressure (pT) for Ideal and Real Gases
Evaluation of the Redlich-Kwong Equation of State
Determination of (CP – CV) for Argon

13. Student Comments
Virtual Substance … made [concepts] real and concrete.
It gave the visual/tactile learner in me a way to grab hold of the topics
[The independent project] was probably the most valuable assignment … I had to think of a problem …, consider the capabilities of Virtual Substance, write a proposal …, and use critical thinking skills to execute and analyze the project. It wasn't just following a simple recipe to obtain some data for a lab report.
[the independent project] was … good preparation for graduate studies.
The most important thing was a good understanding of the chemistry.
1st one – Z vs. P is a picture in nearly all textbooks; Actually generating it made it real

14. Phase Transitions Measure E, P, and V at different temperatures
Combine to get H(T) using H = E + PV
Temperature (K)
H (kJ/mol)
P = 8.5 atm
Ar (actual)
Bp (Argon) ~ atm
DH vap (Argon)= 6.5 kJ/mol
Design experiment to measure Hvap
200 K
80 K
10 K

15. Real Gas Isotherms
Vm (L/mol)
P (atm)
151 K (Tc)
130 K
NIST data
Measure Pressure for series of Volumes at constant Temperature
for Ar
Output agrees with actual data
 Numerically Accurate
Obtain P-V isotherms, Compare to actual data (NIST)
Van der Waals loops present – replaced with straight line; page 22 Atkins
Crtitical temperature Argon = K

16. Polymer Statistics LJ: Lennard Jones – Non-bonded atoms
Or FENE – finite extensible (sion) nonlinear elastic potential used to treat polymers instead of harmonic potential
<R2>1/2 = Nv v = ½ for ideal random walk; v = 0.6 for self-avoiding random walk;
LJ: Lennard Jones – Non-bonded atoms
FENE: Finite Extension Nonlinear Elastic Potential – Bonded Atoms

17. Acknowledgements For More Information: BCCE Symposium Organizers
Our Students
For More Information:

18. More Student Comments
VS could be running in the dorm room while you were doing other homework or laundry.
I will use [Virtual Substance] as a teaching tool when I become a professor.
© Sidney Harris

19. Forms of Various Potentials
Hard Sphere
Billiard Balls of radius s
Soft Sphere
Repulsive forces; typically n=12
Lennard – Jones
Repulsive and attractive forces
FENE – Use instead of harmonic oscillator or Morse Potential to treat polymer binding