Question

I know that its not three and 4 but I can't figure out the answer to this question.

Which reaction is most likely to have a positive ΔSsys?

Which reaction is most likely to have a positive ?

	3O2(g)→2O3(g)
	SiO2(s)+3C(s)→SiC(s)+2CO(g)
	6CO2(g)+6H2O(g)→C6H12O6(s)+6O2(g)
	3NO2(g)+H2O(l)→2HNO3(l)+NO(g)

Answer 1

Which reaction is most likely to have a positive ?
(1)     3O2(g)→2O3(g)
(2)    SiO2(s)+3C(s)→SiC(s)+2CO(g)
(3)     6CO2(g)+6H2O(g)→C6H12O6(s)+6O2(g)
(4)     3NO2(g)+H2O(l)→2HNO3(l)+NO(g)

Answer:(B)
(1)     3O2(g)→2O3(g)
Change in no of molecules, = 2-3 = -1,
no of gaseos moleucles decreases, so entropy decreases as the positional entropy of
gaseous molecules decrease.
(2)    SiO2(s)+3C(s)→SiC(s)+2CO(g)
Change in no of gaseous molecules = 2 - 0 =2
No of gaseous molecules increase. So their positional entropy increases.
Hence entropy increases.
(3)     6CO2(g)+6H2O(g)→C6H12O6(s)+6O2(g)
Change in no of gaseous molecules, 6 - (6+6) = -6. So entropy decreases
(4)     3NO2(g)+H2O(l)→2HNO3(l)+NO(g)
Change in no of gaseous molecules, 1 - 3 = -2. So entropy decreases
The entropy change due to change in liquid and solid molecules are negligible compared to gaseous molecules.