Question

For which of the following processes would the entropy change be positive?
Choose one answer.
a. Hg(l)(45C)----- Hg(l)(25C)
b. H2O(l----H2O(s)
c. He (g) (1 atm)------- He(g)(10 atm)
d. I2(s)------I2(aq)
e. Ag+ (aq) +Br-(aq)------AgBr(s)


I figure that it wasn't A or B but the others not quite certain after reading my Chem book.

Answer 1

I don't understand the a answer so I can't comment.
You;re right about b.
I think c is wrong; entropy should increase the other way.
You know e can't be right; free-wheeling ions in solution to a crystal lattice is negative S.
But for d, if we go from a lattice structure in the solid to a liquid system, the entropy will increase.

Answer 2

It is indeed D.
Think about it this way:
I2(solid) turns into I2(aqueous). This means that, in basic terms, it is melting. Entropy increases when substances melt, vaporize, or sublime.