Entropy, Spontaneous Reactions, and Gibbs Free Energy

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.