I have issues understanding the spontaneity for these processes:
Which of the following processes are spontaneous:
(c) alignment of iron filings in a magnetic field;
(d) the reaction of sodium metal with chlorine gas to form sodium chloride;
The answer given for both (c) and (d) is that the entropy of the system decreases.
This has me puzzled because I don't think that even answers the question. Clearly I would think both (c) and (d) are spontaneous processes. For (c), the iron will naturally align itself in the magnetic field. For (d), I know the reverse reaction is non-spontaneous (table salt does not normally disassociate), so the forward reaction must be spontaneous.
Assuming I am correct, how do I reconcile this with the book answer?
The entropy of the universe increases for any spontaneous process. If we assume the entropy of the system is negative (like the book does) then the entropy of the surroundings must be positive and greater. I don't know what that would mean in this context.
I agree that it makes sense that the entropy of the system is negative. The iron filings are moving to a more ordered state in (c). For (d) there are more micro-states originally since there were more moles of reactants.