then it is referred to as standard molar entropy and represents the entropy at 298 K
and 1 atm of pressure; for solutions, it would be at a concentration of 1 molar. The
larger the value of the entropy, the greater the disorder of the system.
(b) Restatement: In each set, choose which would have the lower entropy (greatest
order) and explain.
(1) SiC(s)
•H 2 O(s) is a polar covalent molecule. Between the individual molecules would
be hydrogen bonds.- SiC(s) exists as a structured and ordered covalent network.
- Melting point of SiC(s) is much higher than that of H 2 O(s), so it would take
more energy to vaporize the more ordered SiC(s) than to vaporize H 2 O(s).
(2) O 2 (g) at 3.0 atm - At higher pressures, the oxygen molecules have less space to move within and
are thus more ordered.
(3) NH 3 (,)
•NH 3 (,) has hydrogen bonds (favors order).
•C 6 H 6 (,) has more atoms and so more vibrations — thus greater disorder.
(4) SiO 2 (s) - Na(s) has high entropy. It exhibits metallic bonding, forming soft crystals with
high amplitudes of vibration. - SiO 2 (s) forms an ordered, structured covalent network.
- SiO 2 (s) has a very high melting point, so much more energy is necessary to
break the ordered system.
Part II: Specific Topics