• A typical amount of material, let's say 1 gram, contains about 6x10^23 molecules: Avogadro's number. ...Continued Below...

  • The water molecules shown above are randomly placed and randomly oriented.

  • Statistical Mechanics uses laws of probability to compute AVERAGE properties of both ordinary materials and of exotic elementary particles.

  • At the root of Stat. Mech. is the Heisenberg Uncertainty Principle.

  • Macroscopic Quantities are: Energy, Entropy (S), Enthalpy (H), Gibbs Free Energy (G), etc.

  • Pressure is the result of the molecules all imparting momentum to a wall.

  • Stat. Mech. is an easy way to treat a very complicated quantum mechanical problem of many particles.

  • The Fundamental Postulate of Statistical Mechanics.

  • Each particle can have a different energy - often quantized, as shown below.

  • Three Systems (Left, Middle, Right) each having available energy levels. The particles in each system are distributed differently among the energy levels.

  • In the laboratory, we can't measure the indiviual energy levels of each particle. Instead we can only measure macroscopic quantities, such as N, V, T, P.

  • The probability that a particle lies in energy state "j" is P_j.

  • The number, N, and total energy, E, of particles is set in a given system.

  • The total energy of a system is the number of particles times the average energy per particle.