1. Spontaneous process; reverse would never be observed, why ??
Entropy and disorder
Consider an isothermal, free expansion of an ideal gas; V1  2V1
Spontaneous process; reverse would never be observed, why ??
Consider the statistical probabilities of final states

2. (a) Case 1: only 2 gas molecules
Probability that both molecules are on left side:

3. (b) Case 2: 3 gas molecules1 2 1 1 3 3 2 2 1 1
Probability that all molecules are on left side:

4. (c) Case 3: 4 gas molecules1 3 4 1 2 3 6 1 2 3 4 1 3 2 4 2 4 1 1
Probability that all molecules are on left side:

5. For 1 mole of gas, probability that all molecules are on left side:
Equal numbers of molecules in each half is the most probable
Boltzmann:
“microstates”
ratio of probabilities