Question

7. a) How might the entropy change when the temperature of of a system is increased as represented in the following figure? You must justify your answer! SKInW; Ko=1.38 x 10-2 co 50 K 25 K b) Describe how a molecules structure might effect the entropy of a system.

Answer 1

a)

The overall effect is increase in entropy with increase in temperature.

In the following figure there is variation in degree of randomness. As the temperature is increased from 25K to 50 K, the degree of randomness also increases. In the first figure, there is a tight pack of molecules at low temperature, at low volume, i.e., there is a very less space around each molecule. The case is changed, when you rise the temperature to 50K, tightness is relaxed and eventually its volume is increased. Now, in the second case, the freedom of molecules to move in random directions is enhanced as there is more space than in the earlier.

25K 50 K

S =KblnW

    = (1.38*10-23)*ln[50/25]

    = (1.38*10-23)*0.6931

   = 0.9565*10-23 J/K/mol

b) effect of structure on entropy

Basically, in two ways the structure of molecule will affect the entropy.

(1) In terms of movement of molecule- The less restricted the movement, the greater is the entropy.

(2) In terms of mass of the atoms and molecules which are at movement—the greater the mass, the greater is the entropy.

Example: C in diamond has entropy 2.377 J/K/mol

                C in graphite has entropy 5.74 J/K/mol