Schedule Today (3/25): Begin Chapter 17 Should have read at least through Section 17.3 Wednesday (3/27): Continue Chapter 17 Read through 17.5 Friday (3/29): Continue Chapter 17 Read through 17.7

“Like Dissolves Like”

Another Question for the 2nd Law: Why don’t oil and water mix? “Like dissolves like”: Tells us ‘what’, but not ‘why’. All molecules exhibit LDFs – shouldn’t they all be attracted to one another?

Forming A Solution Recall: ΔH is a state function, so we can determine it with whatever steps we want as long as we start with the solute and solvent and end with the solution.

Forming A Solution ΔH1? ΔH2? ΔH3? Of: positive, negative, or depends on the solute/solvent, what is the sign of: ΔH1? ΔH2? ΔH3?

Solution Formation - Exothermic Note that ΔH1 and ΔH2 are both positive and that ΔH3 is negative. In this case, ΔHsoln is overall negative (exothermic). Why?

Solution Formation - Endothermic Again, ΔH1 and ΔH2 are both positive and ΔH3 is negative. In this case, ΔHsoln is overall positive (exothermic). Why?

Entropy of Dissolving Not always positive! Why not?

Hydration of Ions

Pressure Effects on Solubility of a Gas As external pressure increases, more gas is dissolved.

Temperature Effects on Solubility Solids in Water Gases in Water