1. Example:
Assume that you have 3 molecules. Each molecule has 4 possible energy states:
0 = 0 (ground state, no internal energy),
1, 2 = 21; 3 = 31
Assume that the total energy of the whole system is 31,
n0, n1, n2, n3 = number of molecules in state 0, 1, 2, 3
 three ways to distribute energy (configurations):
configuration
(ensemble state) n0 n1 n2 n3
tot.particles
k nk
tot.energy
k nkk I 2 1 3
31 II
III

2. Possible configuration, i.e. distributions to molecules A, B, C
ensemble state
mol. state I II
III 3 A B C 2 1
ABC 0 BC AC AB

3. Possible configuration, i.e. distributions to molecules A, B, C
ensemble state
mol. state I II
III 3 A B C 2 1
ABC 0 BC AC AB W 3 6 1
W = Number of possible configurations per given
ensemble state = statistical weight