Energy is associated with the orientation and distribution of molecules in space. Disordered crystals have higher entropy than ordered crystals and diffused gases have higher entropy than compressed gases.

Entropy is also associated with molecular motion. As the temperature of a substance increases, random molecular motion increases hence entropy increases. Figure gives variation of entropy with temperature. At absolute zero `(-273^(@)C)` every substance is in solid state whose particles are rigidly fixed in a crystalline structure. If there is no residual orientational disorder, like that in `CO`, entropy of the substance is zero. Third law of thermodynamics states.
At the absolute zero of temperature the entropy of every substance become zero and does become zero in case of perfectly crystalline structure.
`understand(T to 0)(LtS)=0`
In case of `CO` and `NO` molecules in solid state, there is randomness even at `0 K` due to their dipole moments hence entropy in such cases is not zero even at `0 K`. As the temperature is raised, the molecules begin to vibrate. The number of ways in which the vibrational energy can be distributed increases with increases in temperature and the entropy of solid increases steadily as the temperature increaes. At the melting point (mp) of the solid, there is a discontinous jump in entropy because there are many more ways of arranging the molecules in the liquid than in the solid. An even greater jump in entropy is observed at the boiling point (bp) because molecules in the gas are to free to occupy a more larger volume and randomness increases.
Which of the following process is spontaneous?

Options

A. Solid state
B. Liquid state
C. Gaseous state
D. Equal in all states.

Answer

C