Wednesday, April 13, 2011

Thermochemistry: heat and light

Today I am giving a lecture to a second year undergraduate physics class on "Thermochemistry and the Third law". A few highlights and questions are:
  • A key idea is that of reference states. All thermodynamic state functions (entropy, internal energy, ...)  must be defined relative to some reference.
  • The path independence of changes in thermodynamic state functions means that one can calculate changes (e.g., in the enthalpy) via intermediate reactions.
  • The third law allows definition of a convenient reference state (T=0).
  • Is there a clear way to understand and explain that the "heat of reaction" is the enthalpy change? I still find this a bit confusing. [But pages 33 and 34 of Schroeder's Introduction to Thermal Physics has a helpful discussion].
But, the coolest part of the lecture is the explosions! After all, isn't that is what chemistry is all about? I have some great Chemistry Comes Alive videos of different chemical reactions. Watch the Nitrogen Tri-iodide reaction (detonation)!

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