Day 22: What is the chemical potential?

  1. Homework remark: plot all in same plot!
  2. Homework remark: N not extensive for 2 frequencies, need many (density of states proportional to V)
  3. Chemical potential in first law
  4. Helium balloon: drops, but remains inflated. Osmosis.
  5. Adding more particles becomes harder: dn/dmu > 0
  6. cp of free particles, mu = kB T ln ( n/nQ)
  7. why does not every gas have n=nQ? Particles come from somewhere!
  8. A+B→AB compare muA, muB, muAB
Problems in class
  • Battery: minus Pb, plus PbO2 (Pb core), H2SO4 dilute. Pb + SO4(2-) → PbSO4 + 2e- + 0.8eV and PbO2 + 2H+ + H2SO4 + 2e- → PbSO4 + 2H2O + 3.2 eV
  • two ideal gas systems: Phi1>Phi2, what happens?
  • Barometric law?

Chemical potential is a difficult topic. Make sure you discuss the difference between pressure forcing a movement of particles and chemical potential doing so. The battery example worked well in class, the other two are for wednesday.

Day 23: More chemical potential

  1. First law again
  2. Differences are important
  3. What is diffusion?
  4. Entropy of mixing
  5. Lead in to osmosis
  6. Chemical potential is internal plus external
  7. Phi1,2 example with ideal gas
Problems in class
  • Osmosis (guided!)
  • Barometric equation

Asking what is chemical potential gives responses related to energy (bonds, etc). Using a diffusion example than shows that entropy of mixing based processes are also important. In asking about the prediction of osmosis three answers were received, left up, down, same. I tried to have students work through this, but the problem is too hard for it. Why is the chemical potential of water the only relevant quantity? Why can we expand it? I like the idea of using osmosis as an example, but it needs much more guidance.

Day 24: Title

  1. Chemical potential internal, external
  2. Phi1,2 example
  3. Barometric equation
  4. Surface problem in class
Problems in class
  • Surface absorption

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