1. Molten gold solidifies.
2. Gaseous Cl2 in the stratosphere to form gaseous Cl atoms.
3. Gaseous CO reacts with gaseous H2to form liquid methanol, CH3OH.
4. Calcium phosphate precipitates upon mixing Ca(NO3)2(aq) and (NH4)3PO4(aq).
Remember: Increasing entropy = increasing randomness. Gasses are the most random, then liquids, then solids, so any reaction which produces more gas/ liquid than you started with has positive delta S. Similarly, the more separate stuff there is, the more randomness, therefore any reaction turning 1 thing into two things (all in the same state) will have +ve delta S
So;1) Solidifying, Liquid -> Solid, randomness goes down so Entropy goes down, so -ve delta S
2) Stuff splitting to form more stuff in the same state; Cl2 -> 2Cl, number of gaseous moles on LHS is one, on RHS is 2, therefore stuff split up, more randomness, +ve delta S
3) Gas(es)-> liquid, randomness goes down, -ve delta S
4)Liquid -> solid ppt. (well, technically not liquid, actually in soln, but molecules have similar properties to if they were liquid) (ie. no fixed lattice, random motion therefore big randomness)
So Liquid/aqueous ->solid, randomness goes down, delta S -ve
I hope you understand how to do these now, it’s a tricky topic to grasp, but just remember; state changes, gases are most random so delta s -ve if gas to anything else, and splitting stuff without state changes, side with more split up stuff is more random and so has more/ higher entropy