Principles of Chemistry II

1/26	Mon	Phase changes and heating curves. Went over the different areas of a heating curve for a substance. Used the heating curve help sheet from this web site. Described how to solve ice + water + steam type problems. Phase diagrams. Showed the 3 lines that make up the diagram. Key features: the critical point and the triple point. Be able to interpret a phase diagram.
1/28	Wed	First reviewed free energy and the formula ΔG = ΔH - TΔS from Chapter 10. Spontaneity (ΔG) is driven by BOTH ΔH and ΔS. Endothermic processes DO occur spontaneously when ΔS is positive and the temperature is high enough so that the TΔS term offsets the ΔH term. Also reviewed what lattice energy is and HOW we show it. Then I showed how a solution is formed from the solute and the solvent. Went over the 3 steps show on page 828 of your book. These steps combine to give the heat of solution, ΔHsoln. The steps are shown nicely on page 830 in your book.
1/29	Thu	Homework 1 is due by 12 noon
1/30	Fri	First, I told you to review/read Chapter 4 - especially the first 3 sections. The dissolving process for ionic compounds is shown there. Chapter 17 covers the thermodynamics of this physical change (solid to dissolved solid). Discussed hydration energies and what factors influence them - charge-to-size ratio of the ion is proportional to the hydration energy. Some ions pull in water so close that there can be a NEGATIVE ΔS for the dissolving process - the book gives examples of LiF and CaS. Discussed hydrophilic and hydrophobic species. The rule of thumb - likes dissolve likes. How does temperature affect solubility? Depends on the sign of ΔH. If ΔH is positive, increasing T will increase solubility. It is opposite if ΔH is negative. Solubilities of gases in solution. Henry's Law - the pressure of a gas above a solution is directly proportional to the concentration IN the solution.
1/31	Sat	Homework 2 is due by 6 PM

Watch out for varying concentration terms in these equations: mole fraction, molality, and molarity.

2/2	Mon	Went over the 4 Colligative properties in class: (1) vapor pressure lowering, (2) boiling point elevation, (3) freezing point depression, (4) osmotic pressure. Each colligative property has an equation to go with it.
2/4	Wed	Showed how you can use these colligative properties to calculate molecular weights of solutes. Method: Measure KNOWN mass of solute into KNOWN amount of solvent, then measure the colligative property. The colligative property will give you the concentration, and from the concentration and amounts used you can get moles. MWt = grams/moles. Introduced the van't Hoff factor for strong and weak electrolytes. When a soluble salt dissolves, you get even MORE ions in solution than you originally thought. What you MIX is the "stated" concentration. The stated concentration does NOT consider any ionization or dissociation. What you actually get is the "actual" or "effective" or even "total" concentration. Ratio the two and you get the van't Hoff factor, i. i can have "ideal" values of integers. For example NaCl has i = 2.0, while FeCl3 has i = 4.0, ideally. ACTUAL i values depend on how much ion-pairing is going on, or how much ionization is occurring for weak electrolytes.
2/5	Thu	Homework 3 is due by 12 noon
2/6	Fri	Worked some colligative properties problems using i. Know how to solve for i and also how to use the ACTUAL colligative property and "back-track" to the actual concentration and then extract the percent ionization for a weak electrolyte. I did this in class for a 0.25 M HX solution at 300K with an osmotic pressure of 6.924 atm. This back-tracked to a 12.5% ionization for HX.
2/8	Sun	Homework 4 is due by 3 PM. Galye's Review from 4-5 PM in WEL 2.224

2/9	Mon	Talked about Exam 1. 26 questions all equally weighted. Gave out some "always" solubility rules: ALL group IA metal cation salts are soluble. ALL nitrate and acetate salts are soluble. AND.. ammonium salts are soluble. Tried to start up on chemical equilibrium. Tried to get you to see the differences in different ΔG's - when its negative or positive, big number vs little number. Drew free energy curves that showed free energy vs composition of the mixture. READ pages 436-439 in your book... that's chapter 10 section 10 and 11. Finished with what a mass action expression looks like... will start there on Wednesday. from 6-7 PM in WEL 2.246
2/10	Tue	EXAM 1, 7-9 PM