O2 16 An oxygen O2 molecule is adsorbed on a patch of surface ( see sketch at ri

Question

O2

16

An oxygen O2 molecule is adsorbed on a patch of surface (see sketch at right). This patch is known to contain

784 adsorption sites. The O2 molecule has enough energy to move from site to site, so it could be on any one of them.

Suppose part of the surface becomes inaccessible, so that only 324 adsorption sites are now available for the molecule. Calculate the change in

entropy. Round your answer to 3 significant digits, and be sure it has the correct unit symbol.

O2

16

Explanation / Answer

The Boltzmann formula for the entropy is given as:

S = k ln W

Here k is Boltzmann's constant = 1.381x10-23 J/K

W is the number of energetically equivalent possible microstates or configurations of the system.

For 784 adsorption sites, S = (1.381x10-23 J/K) x ln(784) = 9.20 x10-23 J/K

For 324 adsorption sites, S = (1.381 x10-23 J/K) x ln(324) = 7.98 x10-23 J/K

Change in entropy, S = 9.20 x10-23 J/K - 7.98 x10-23 J/K = 1.22 x10-23 J/K

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