Entropy, Spontaneous Reactions, and Gibbs Free Energy Scribe Post by Juliette O. 3/4/14
Agenda
First, we turned in the Hess's Law Lab Write Up, and for those who did not finish on Friday the Thermochemistry quiz. We then picked up the three pages of notes on Entropy, Spontaneous Reactions, and Gibbs Free Energy, and the worksheet (2 sheets) for homework. These are posted on moodle. We were reminded that the test is on Thursday-- remember to print the review packet and study it. The video is posted, and there will be a study session at 7 in the morning on Thursday. Next, Mrs. Friedmann showed us a quick demonstration on entropy and we then went over the notes. Finally, we went over the first two problems on the homework.
Notes
Homework Questions 1 and 2
Introduction to Notes
Enthalpy is the energy in the bonds of chemicals, but enthalpy and entropy changes allow us to predict if the reactions reacts spontaneously.
Entropy: measure of disorder in the universe, as in all the systems and surroundings
Processes increase disorder.
Demonstration and Notes
Mrs. Friedmann took out a deck of UNO cards and spread them out haphazardly on the table. She pointed out that without work, someone physically organizing them, if thrown out on the table the cards are unlikely to end up in a neat stack. Work is required for that to happen. The universe is more likely to fall into disorder than order because of this.
Order <---Requires Work-------Naturally Occurring--> Disorder
Spontaneity=disorder, and you need work to get order.
Example: my room had increased entropy at the end of the week!
Mrs. Friedmann then split the deck of cards in half and put an organized half on the left side of the room and the disordered on the right side of the room. If the messy, disordered deck is on the right and the ordered deck on the left, the disordered in the products have a higher entropy. Therefore, if entropy is higher on products and lower on the reactants side, + number for delta S.
REACTANTS --------> PRODUCTS Spontaneous and Positive (the universe is naturally
less entropy more entropy like this b/c it is more likely to land in disorder)
more entropy less entropy Negative number for delta S
Example of a spontaneous reaction: fire burning-- it will continue burning and will light in the right conditions.
However, many spontaneous reactions happen slowly, for example, the reactions in the body are spontaneous but occur slowly. Enzymes speed up these reactions by decreasing the activation energy in our body. Even when enzymes are involved as catalysts, the reaction is still spontaneous!
Crash Course on Entropy:
Homework
3 Webassigns, two due tonight, one due tomorrow
Worksheet (2 sheets; questions 1 and 2 done in class, 3 and 4 to be finished individually)
Work on review packet! The video is posted on moodle.
Study for test Thursday! Study session is at 7 AM Thursday morning.
First, Mrs. Friedmann checked in our homework. The homework was two worksheets, the Intermolecular Forces table and the eight questions on the Intermolecular forces worksheet. Next, we had a discussion about Solar Roadways which was brought up yesterday and other such innovations. We then went over the homework and Mrs. Friedmann answered our questions about the worksheets, web assigns, and review packet. We were supposed to also complete a lab, the Physical Properties of Liquids Lab, but we did not have time to complete it.
Class Discussion
At the beginning of class, we watched a video about Solar Roadways. According to the website, "The Solar Roadway is a series of structurally-engineered solar panels that are driven upon. The idea is to replace all current petroleum-based asphalt roads, parking lots, and driveways with Solar Road Panels that collect energy to be used by our homes and businesses." More information can be found on this website: http://www.solarroadways.com/intro.shtml, and the video above is a short documentary about the innovation.
We also discussed the idea that it is the small solutions that make the greatest impact. For instance, in third-world and developing countries especially in Africa, people have to trek for miles carrying heavy tanks to get water, and usually those making that trek are women. The Hippo Water Roller was invented as an easier, less taxing way of carrying water. The video above details the innovation.
We also discussed solar power, and how we can innovate so that we are not so reliant on fossil fuels. Illinois uses a lot of nuclear energy, yet even nuclear energy comes with its own problems. There is a very interesting growing field called biophotovoltaics, which is working on artificial photosynthesis and how we can harness the power of the sun and plants for solar power. Specifically, a recent paper by Andreas Mershin and some researchers at MIT details how Photosystem I can be aggregated from discarded crops or timber, stabilized by some chemicals, and spread out on a "nanoforest" of semi-conducting electrodes of ZnO nanowires and TiO2 nanostructure that can produce an electric current when exposed to light. This could mean that in a few years people in third-world and developing countries could use discarded plants, a bag of chemicals and some written instructions and paint this/install this on their roof and have solar power. Right now the efficiency is only at 0.1-0.8% but the field is clearly advancing and such an innovation would be extremely useful and life-changing in developing countries. Click here for the link to the paper on this biophotovoltaics innovation
Homework
We went over both of the worksheets in class today. Important things to remember about intermolecular forces:
Nonpolar--> main IMF London Dispersion Forces even though LDF is at work in every molecule (symmetrical)
Polar --> main IMF Dipole-Dipole (assymetrical)
Usually, if polar w/out a hydrogen attracted to O, N, F (FON) --> dipole/dipole
If Nonpolar --> London Dispersion Forces
Polar w/ H attracted to F, O, or N--> Hydrogen Bond
In addition, these intermolecular forces are on a continuum. We learn the extremes, and the muddy area is for experimentation. H Bond (strongest) <----------> London Dispersion Forces (weakest)
Key to Worksheet 8 Questions
We also discussed CH4O, methanol. The lewis structure is to the left. Remember, any molecule with an O-H bond is an alcohol (though not necessarily alcohol as in beer and wine). In CH4O, the main IMF is Hydrogen Bonding, which is stronger and better at sticking molecules together and therefore is the stronger/main IMF. Mrs. Friedmann also showed us the lewis structure for ethanol, which is what is in the beverage alcohol. The lewis structure for ethanol is above. Ethanol also has an O-H bond so has H-bonding. Methanol is wood alcohol, a paint thinner that is dangerous to drink. During the Great Depression and Prohibition, alcoholics drank methanol as an alternative to beer and wine. The body metabolizes ethanol into ethaldihyde, however that same enzyme does the same chemical reaction to methanol and turns it into formaldihyde. Formaldihyde is dangerous because it freezes molecules into place and preserves them, essentially "pickling" the body. The "cure" is to drink a lot of alcohol.
In addition, we discussed hydrocarbons. With an extremely long chain of hydrocarbons, even if there is an oxygen connected to a hydrogen, the main IMF would be London Dispersion Forces because of the great amount of hydrocarbons. The longer the non-polar side, the stronger the LDF and the increased viscosity.
Key to Worksheet w/ Table
On the second worksheet with the table, the answer to the motor oil question is as follows on the key:
Since motor oil is needed to quickly coat all surfaces of an engine to keep them from getting too hot, a low viscosity material is better than a high viscosity material.
*Viscosity= measure of how well substances flow
*contains H-bond which means high velocity, motor oil has LDF only so it has low viscosity
We also went over sigma and pi bonds, that a pi bond is the last pair of electrons for example on the S in SO2 which spreads out and balances the structure. A pi bond is ultimately an area of space electrons can occupy, orbitals available. The key is that electrons don't stay stuck in between 2 atoms in a pi bond, if there is an empty pi bond they will smear onto it and occupy the entire space, and we show resonance to demonstrate this.
Had we done the lab, we would have worked with:
1) Hexane--> no polarity so main IMF is LDF and would evaporate quickly and have a low boiling point
Hexane
2) Vegetable Oil --> LDF and Dipole-dipole and polarity, but the predominant intermolecular force is LDF
3) Water --> Hydrogen bonding
Homework
Study for Unit 8 test tomorrow! A good way to study would be to work on the review packet. The key is posted on moodle. The next scribe post author is: Valerie Korol
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