# Predict the sign of ΔSsys for each of the following processes.?

0

1. Molten gold solidifies.

a. ΔSsys>0

b. ΔSsys<0

2. Gaseous Cl2 in the stratosphere to form gaseous Cl atoms.

a. ΔSsys>0

b. ΔSsys<0

3. Gaseous CO reacts with gaseous H2to form liquid methanol, CH3OH.

a. ΔSsys>0

b. ΔSsys<0

4. Calcium phosphate precipitates upon mixing Ca(NO3)2(aq) and (NH4)3PO4(aq).

a. ΔSsys>0

b. ΔSsys<0

• 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

🙂

Also Check This  If a person is in their 40’s are they considered young or old?