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

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

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