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). When you add more stuff, the pressure inside the balloon does not change (???), but it 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 way 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, but in reality 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...

At this station you will find one large 5 gallon bottle, one small bottle, a thermometer, some film canisters, baking soda, and vinegar. Your task is to determine the number of moles of gas inside the 5 gallon bottle, answers some related questions and then do one small experiment.

The moles of gas in a container can be determined using the ideal gas law:

PV = nRT where P = pressure V = volume n = number of moles of gas R (gas constant) = 0.08206 (L•atm)/(mol•K) T = Temperature

PROCEDURE Step 1: Enter “Ideal Gas Law” heading into your lab notebook. Step 2: Write the ideal gas law in your notebook. Step 3: We are interested in calculating the moles of gas (n). Rearrange, in your notebook, the ideal gas law equation so that the equation now reads “n = something.” Step 4: Determine the values needed to calculate the moles (n) of gas is each container (big and small); show the calculation in your notebook (use P = 0.9818 atm and T=298 K). Note that units are VERY important; some unit conversion is required. Step 5: Complete the following calculation in your notebook: If all the moles of gas in the 5 gallon bottle were placed in the small bottle, what would the pressure be inside the small bottle? Step 6: Complete the following calculation in your notebook: If the moles of gas in the 5 gallon bottle were heated to the temperature of 75.0 °C, what would the pressure be inside the 5 gallon bottle? Step 7: Consider what would happen if gas was generated inside of a confined volume? Let’s try this.

Baking soda (NaHCO3) + Vinegar (acetic acid)  CO2 gas + other products

- add ~ 5 ml of vinegar to the canister, - place ~1/2 tbsp of baking soda in a Kimwipe and make a small package by twisting the top. Cut off the excess Kimwipe, - locate the “snap-on” cap for the canister, - Quickly, drop the baking soda in the canister and snap the lib in place...set on bench top…and wait.

Step 8: Record your observations in your notebook…yes you can do the reaction again if you desire. Step 9: PLEASE rinse the film canister and lid with water and wipe down the lab bench.

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

worksheet coming soon...