Entropy and Delta S?

Question

Predict the sign of the entropy change, ΔS˚ , for each of the following reactions.

A) Pb2+(aq) + 2Cl-(aq) -> PbCl2(s)
B) CaCO3(s) -> CaO(s) + CO2(g)
C) 2NH3(g) -> N2(g) + 3H2(g)
D) P4(g) + 5O2(g) -> P4O10(s)
E) C4H8(g) + 6O2(g) -> 4CO2(g) + 4H20(g)
F) I2(s) -> I2(g)

Which are positive and which are negative?

Answer 1

Look for ones where a solute is going into solution, or where there are more moles of gas on the RHS than the LHS.

a, d are negative, because they reverse this process.
b, c, e, f are positive.