Schedule1 Schedule2 Schedule3 Schedule4
Schedule to Exam 4
| Date | Day | Topics |
|---|---|---|
| 11/7 | Fri | Discussed Exam 3 and started Chapter 9 on Thermodynamics. Discussed the IMPORTANCE of recognizing state functions and that they are truly PATH independent. Most of our properties that we measure are state functions - the exceptions are heat (q) and work (w). Heat and work ARE path dependent. You MUST define the path in order to calculate heat and work. I covered the most obvious ways to calculate heat and work. heat = q = C ΔT is very straight forword: heat capacity times temperature change will equal heat transferred. The heat capacity (C) can be split into 2 parts also: mass x specific heat or moles times molar heat capacity. Work done by the system (expanding gas, pushing something up..) is equal to the negative of the external pressure times the change in volume (-PΔV). Sign convention: +q is heat flowing INTO the system. -q is heat flowing OUT OF the system. +w is work done ON the system (compression typically). -w is work done BY the system (expansion work typically). |
| 11/10 | Mon | Showed the "other" way of calculating work which is assuming that the change in volume (ΔV) is due to a change in gas moles (Δn). This leads to w = -ΔnRT. Then substituted the 2 terms for work (-PΔV and -ΔnRT) into the equation ΔE = q + w. Also showed a proof that heat transfer at constant pressure is equal to change in enthalpy ( qp = ΔH). When over coffee-cup calorimetry and bomb calorimetry. PLEASE refer to the Calorimetry Help Sheet that is on our website. |
| 11/12 | Wed | Went over (in detail) the differences in molar
heat capacities of ideal gases. There ARE differences in monatomic gases, linear gases, and
non-linear gases. Each degree of freedom in a gas adds another 1/2R to the molar heat
capacity (Cv,m). For Cv,m: mono = 3/2R, linear = 5/2 R, and non-linear
= 6/2 R. When heating at constant pressure WORK (w) is done and the cost must be paid by the
incoming heat. This means that the constant pressure molar heat capacity is BIGGER than the
constant volume molar heat capacity: Cp,m > Cv,m but by how much? One R
unit more in each of the 3 cases. Memorize this: Cp,m =Cv,m + R.
Hess' Law was introduced. You combine the enthalpy changes for individual steps (reactions)
in order to get the overall net reaction enthalpy change. The sum of the steps equals the
overall process. This actually works for ALL state functions, not just enthalpy changes. |
| 11/14 | Fri | Recapped the first laws for ΔE and ΔH. More on Hess' Law. Introduced what a "formation" reaction is. You write out a balanced chemical reaction such that only elements (in their natural state at 1 atm and 25°C) a listed as reactants and ONLY ONE mole of product (a single product) is formed. These formation reactions are the reactions that are listed in thermodynamic tables in books - yes, even your book... see Appendix 4. Using heats (enthalpies) of formation, you can then sum all the products and subtract all the reactant's ΔHf's to get the overall reaction enthalpy change, ΔHrxn. Also revisited (with Hess' Law on our minds) the way to calculate ΔHrxn's via Bond Energies (see 9/29 on our schedule also). And at last, I told you how to calculate average bond energies using Hess' Law. Remember that your "target" reaction must BREAK all the type bonds that you are checking. Get ΔHrxn for that target reaction and then DIVIDE by the number of bonds broken - THAT'S how you get the average. |
| 11/17 | Mon | Started chapter 10. Defined what "spontaneous" means
in terms of thermodynamics. Defined the 2nd Law of Thermodynamics. Defined Boltzmann's formula
for statistical entropy: S = k ln W Also used calculus to get the (reversible) work and heat for an isothermal expansion: w = -nRT ln(Vf/Vi) and q = nRT ln(Vf/Vi). Then used the idea of microstates being proportional to volume and used Boltzmann's formula to get ΔS = nR ln(Vf/Vi) which then lead to realizing that entropy change is really just a measure of the reversible heat flow divided by the temperature: ΔS = qrev/T. |
| 11/18 | Tue | H12 is due by 11:59 AM (this is by noon) |
| 11/19 | Wed | Change in entropy is q(rev)/T. We took that and put our knowlege of q into it and wrote out some new equations for ΔS. One for isothermal expansion of an ideal gas, one for changing temperature of a substance, and one for phase changes (transitions). I pointed out that the discussion in section 10.2 is WORTH you reading a few times to SEE just how the heat and work calculate out for 2 points on a PV isotherm. As Zumdahl points out, the heat and work values DO depend on the path picked (1 step, 2 steps?, many steps?). Although in every case, ΔE = 0 because q = -w for isothermal physical processes. I then tried to get you to STUDY the ramifications of the equation: ΔS(univ) = ΔS(sys) + ΔS(surr). Sign of ΔS(univ) will tell you about spontaneity. |
| 11/21 | Fri | Introduced our last thermodynamic state function, Gibb's Free Energy (G).
Free energy is simply defined as G = H - TS. After some simple assumptions we found that the
change in free
energy of the system is directly related to the change in the entropy of the universe:
-ΔG/T = ΔSuniv or
ΔG = -TΔSuniv
We also looked at a Table of thermodynamic values and saw that ΔHf°, ΔGf°, and S°, were listed there. We will "track" spontaneity more with ΔG;, than with ΔSuniv. Probably the most important formula we learned for the day was: ΔG = ΔH - TΔS |
| 11/24 | Mon | Continued with ΔG = ΔH - TΔS . Specifically, we looked at the sign on ΔG and how it was affected via the signs on ΔH and ΔS. There were 4 cases in all which are summarized in your book in Table 10.6 on page 424. Two of those cases allow for ΔG to equal zero which is the definition of equilibrium. I worked an example of calculating boiling point using only thermodynamic table values. This method IS an approximation due to the fact that our look-up values for ΔH° and ΔS° are 25°C values. Luckily, ΔH° and ΔS° don't change "much" with temperature, so we can use the 25°C values and still get a good approximation of the equilibrium temperature: Tequil ≅ ΔH°/ΔS° |
| 11/26 | Wed | NO CLASS!! Happy Thanksgiving!!! (deadline for H14 is noon!) |
| 11/27 | Thu | Thanksgiving. TX vs A&M at 7PM on ESPN. |
| 11/28 | Fri | no class |
| 12/1 | Mon | Chapter 10 |
| 12/2 | Tue | H13 is due by 11:59 AM (this is by noon) |
| 12/3 | Wed | Chapter 10 |
| 12/4 | Thu | EXAM 4, 7-9 PM |
| 12/5 | Fri | day 42 - last day of class - Review for Final Exam. |
| 12/8 | Mon | NO CLASS DAY : last chance office hours |
| 12/9 | Tue | NO CLASS DAY : last chance office hours |
| 12/10 | Wed | first day of UT final exams |
| 12/11 | Thu | |
| 12/12 | Fri |
| 12/15 | Mon |
Final Exam for 53745 (1pm section) from 2-5 PM in WEL 1.308 and WEL 1.316 |
| 12/16 | Tue |
Final Exam for 53740 (11am section) from 9-12 noon in WEL 2.224 and WEL 1.308 |
| 12/17 | Wed | |
| 12/18 | Thu | |
| 12/19 | Fri |