PChem312 s22 w2

...return to Chem 312 - home

Mon, Jan 17, 2022

Announcements

1) Good Monday morning and happy Martin Luther King Jr. Day! If you have not recently seen/heard the original August 28, 1963 (I was 4 month old) MLK Jr. speech, i suggest you watch it now. Here is the full 17 min audio of the speech and here is a shorter 6 min "highlight" video. This is without a doubt a beautiful and timely speech. A particular part resonates with me as a teacher...he notes, "I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character."

2) Lab this week will be a hybrid experience...ie. there will be an assignment/worksheet posted below as well as meeting in-person in small groups of 4. Please review the list below to see when you are scheduled to show up. Please be on time, there will be a quick intro prior to you can starting your glassblowing; if you miss this, it will result in a timing problem.

Class Assignment

1) On Friday you were asked to read Section 1.3...by today. As noted, this section has a collection of bold terms that should now be aded to your notes. The main point of this section is to point out that when we engage in discussion of thermodynamics, we must be specific about every detail of the system and to clearly differentiate this from the surroundings. Consider the examples below:

- If you wish to carry a cup of hot coffee from the cafeteria to your first lecture, you will choose a system (a container) that is closed (so it does not spill), is adiabatic (so it does not loose heat), and has a fixed volume/boundary (because it would be weird if it didn't). The coffee would be considered isolated from the surroundings in a closed system. The company YETI would not be able to charge so much for a travel coffee mug if it did not seal well (remain closed as opposed to open), if it lost heat on sitting (diathermic as opposed to adiabatic), or if the steel walls where thin and easily dented.

Thermal imaging (IR) can be used to evaluate heat loss...we have one of these cameras.

- Balloons are interesting. The most important feature of a balloon is that the volume can change (boundary is not fixed). [Edited sentence follows, 1/21/2022, bes] When you add more stuff, the pressure inside the balloon does change, but it mainly responds by increasing volume. Under most cases, a balloon is considered a closed system, but in reality, helium can diffuse through the walls of a latex balloon and hence are not truly closed. This is why we have Mylar balloons that can hold helium for months. It would be weird if a balloon attempted to be adiabatic...not even sure how this would be designed since the stretchiness of the walls is required to expand, resulting is thinner walls...balloons are by design diathermic.

As noted above, when you add air/gas to a balloon, the volume changes, and the pressure changes as well. In your notes, please draw a graph of pressure (y-axis) and volume of air (x-axis) and ass-u-me the balloon will burst at 30 psi, when 5 liters of air has been added.

Continuing with the balloon...watch this weather balloon video then answer the questions below in your notes:

• why did the balloon pop at high altitudes? (yes, this appears to be a compilation of multiple flights although it is not stated in the video comments).
• Could you calculate the change in volume as a function of altitude? how might you do this?

2) This section (1.3) introduces the 0th Law of thermodynamics. It is the case that laws are numbered 1, 2, etc. but in this case it became evident after the 1st, 2nd, and 3rd laws were defined, that there was a clear observation that should have been acknowledged by a "law." The 0th Law of Thermodynamics says, thermometers work...or more formally what is written in your textbook (p. 11).

3) Sec 1.4. This section has been previously discussed in Gen Chem, but here the authors add a little math-crap to again show that math is a very useful tool. To remind you of the Gen Chem "Gas Laws" lab you did i ask you to redo the calculations using the ideal gas equation you did a few years ago...

Complete steps 3-6 in your notes...the small bottle had a volume of 50 mL.

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Tues, Jan 18, 2022

Announcements

1) We will begin training in glass blowing. Will will have a short "how-to" intro and then each of you will be given ~50 mins to make a rudimentary thermometer. Please attend lab (CSB 373) at the time listed below:

- from 2-3 pm Sara S., Sarah P., Jordan K., Lucas

- from 3-4 pm Jonathan, Eliza, Isaac, Alex

- from 4-5 pm Zoie, Joseph, Jordan P., Madeline

- from 5-6 pm Sreya, Brendan, Matt

Lab Assignment

Due by 6 pm TODAY (email Excel file)...make this Heating-Cooling Curve for Water. So that i am very clear, you will open Excel, enter in the values shown for the constants (or global variables), and then use these constant to do the calculations and then graph. In a best case, you would come to CSB (either 377 or 378) and work on this assignment. IF you have questions, you can stop in lab after i do a 10 min intro to glassblowing. :Note: This work is to be done independently...ie. each student will enter all data into their own Excel file; please assist your friends but never touch their keyboard.

Wed, Jan 19, 2022

Announcements

1) Welcome to 5G (5th Generation) cell service. This technology, which in part uses the C-Band (~4GHz) microwave technologies, may interfere with the altimeter on commercial airlines, hence thee has been a lot of concern over the launch. The cell phone companies have agreed to not use this frequency around airports for the time being...stay tuned.

2) Great job in lab. There is a lot more to learn about glass and glass blowing, but i just wanted to give you a brief experience. If you like doing this, let me know; I usually leave at least 2 torches out on the lab bench all semester long. As you noticed, glass tubing comes in many sizes, some have a standard wall thickness (you did not work with this), some have a thick wall (your first tubing), and then some are specialized like the capillary tubing (very thick wall/very narrow opening). As you might have expected, when ordering glass tubing, you have a few parameters that need to be specified. First, you need to make sure you are purchasing borosilicate glass and not soda lime glass or a glass that has some invisible coating. Borosilicate glass, sometimes labels as "Pyrex" or "Kimex," is made using a well defined composition and hence it has the same coefficient of expansion (COE). As you see in the picture below, glass tubing has an ID (inner diameter) and an OD (outer diameter). You can also specify the wall thickness, but you really only need to specify 2 of the three parameters when ordering.

Next week in lab, we will fill your thermometer with ethanol, seal it, and then calibrate.

Class Assignment

1) continuing with Sec 1.4: Equations of State/Ideal Gas Law

- Review: There is a STATE --> described by STATE VARIABLES --> the relationship between the state variables is the EQUATION OF STATE (variables).

- Equations of state allow us to have predictive powers.

- Q: Why do we fit data to math equations? A: data reduction...x/y data set of 100 points can be reduced to slope and y-intercept.

- PV=nRT or PV=NkT

• Units or "Dimensional Analysis" is VEY important. Write out in your notes the work that shows nR = Nk;

- R = 0.08314(bar*L)/(mol*K),

- k = 1.38e-23 J/K, <-- really J/(molecule*K)

- N = 6.022e23 molecules per mole or Avogadro's number

nR = 1 mole * 0.08314(bar*L)/(mol*K) = 0.08314 (bar*L)/K

Nk = 6.022e23 molecules * 1.38e-23 J/(molecules*K) = 8.31 J/K

so does 0.0831 (bar*L)/K = 8.31 J/K ?

to equate these units you need to convert bar*L in to Pascal*m³ → see Table 1.1 or the front inside cover 1 bar = 1e5 Pa and 1 L = 1e-3 m³; so 1e5 * 1e-3 = 100, so 0.0831 (bar*L)/K *100 = 8.31 (Pa*m³)/K.

so does a Pa*m³ = J...yes it does...a Pa = kg/(m*s²) * m³ = (kg*m²)/s² = J

What a pain in the ass...right?

- Intensive (density)/Extensive (mass/volume) properties.

2) Sec 1.5: Brief Intro to a Real Gas

So although the ideal gas law is pretty good, not all gases are "ideal." So that we have a general understanding of how gases behave, there is the "Kinetic-Molecular Theory of Gases"...it states:

a. A gas consists of a collection of small particles traveling in straight-line motion and obeying Newton's Laws.

b. The molecules in a gas occupy no volume (that is, they are points).

c. Collisions between molecules are perfectly elastic (that is, no energy is gained or lost during the collision).

d. There are no attractive or repulsive forces between the molecules.

e. The average kinetic energy of a molecule is 3kT/2...more on this later.

A guy named, van der Waals put together an equation which took into a account that there ARE interactions between gas atoms/molecules (d above are not totally true). Eq. 1.22 (p 15) is the van der Waals equation...of state for non-ideal/real gases.

- Please use Excel to reproduce this figure; the van der Waals coefficients can be found here. PLEASE use global variables/universal constants/constant values so that once the Excel file is completed, you can change these parameters and the rest of the spreadsheet will update. If you don't know what a global variable is...ie. B3 vs. $B$3...please see https://youtu.be/6y_Nf6uvPxw

END