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 assume the balloon will burst 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?

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...