Lecture 3

Readings

http://umdberg.pbworks.com/w/page/68405604/The%202nd%20Law%20of%20Thermodynamics%3A%20%20A%20Probabilistic%20Law%20%282013%29

http://umdberg.pbworks.com/w/page/68405609/Implications%20of%20the%20Second%20Law%20of%20Thermodynamics%3A%20Entropy%20%282013%29

2nd Law of Thermodynamics

Coin Flips:

Microstate = H T T H H T H

Macrostate = 4 Heads, 3 Tails

• Each macrostate has number of arrangements ( microstates ) that correspond to the macrostate

• So arrangements can be:

  • A specific sequence of coin flips
  • The locations of every molecule
  • The energies of every molecule

• One statement of 2nd law:

If the number of particles is large, a system will spontaneously move toward the macrostate with the greatest number of microstates

Entropy

• Symbol = $S$$S$

• $S=k_B\ast ln(W)$$S = k_B * ln(W)$

  • Where $k_B$$k_B$ is the Boltzmann constant = $1.38\ast {10}^{-23}Joules/K$$1.38 * 10^{-23} Joules/K$
  • W is the number of microstates

• $S$$S$ is a value for a specific state ( = thermodynamic state = macrostate ) of a system

• Higher $S$$S$ means that the (macro)state is associated with a larger number of microstates = lots of arrangements are possible to give the same (macro) state