Question

Give reasons for the following :
(a) Why the heat produced be different if same mass of diamond and graphite are burnt in oxygen?
(b) The dissolution of ammonium chloride in water is endothermic still it dissolves in water.
(c) A real crystal has more entropy than an ideal crystal.

Answer 1

"(a) If "same mass" of "diamond and graphite" are "burnt" in the oxygen, the heat produced is different. Because "diamond" has "three dimensional" structure whereas graphite has hexagonal rings in each layer.

(b) Yes.

During the dissolution of "ammonium chloride" in water, entropy increases. That is $\Delta s$ is positive. We know that$\Delta H$ is positive here.

But if $T\triangle S\quad >\quad \triangle S$,

Then, $\triangle G\quad =\quad \triangle H\quad -\quad T\triangle S$

According to above equation  G will be negative.

Hence, the process is spontaneous.

(c) Due to the "presence of defects", a real crystal can have some disorder. But the ideal crystal has no disorder. That is why "real crystal" has "more entropy" than "ideal crystal". "