Teacher: check the web. He isn t here, so I will have to yell at him.

Transcription

1 September 9, 2003 (Reading from page of announcements) working offline! Remember neo accts are important. (Reading from page of NOTES) I am answering your s; it just may take some time. I have information of how to work with your packet that is easier to work with than the information from your packet. I went to the bookstore; they can order the old editions. I put books on reserve at the Annex. There is a backside to the green sheet, which is organic nomenclature. For the first exam: you must know the Names and formulas, not the structure this time. That is all on the back of that sheet. Review by Silvia, this Thursday from 7-9, for the lab. My review on Sunday was just background for the lab, coming up, which was for the ionic equation. Thursday she will go over that again. These reviews will help you write up the laboratories you have done and prepare for the next one. (Reading from page notes, you can dye your goggles if you go by room 400 on Friday). Female Student: is there an SI-? Teacher: check the web. He isn t here, so I will have to yell at him. Page 1 of 1

2 Male Student: where do you buy goggles? Teacher: well the goggle people will come by and sell them in your labs. If you miss that time, graduate students will sell them between times or I can sell you some. Male Student: does the skill builder require a cd? Teacher: you will have to buy it from the bookstore; you must ask for it as it s under the counter. If you bought it from the web, then you don t need the CD. This will be the last year to be able to buy it on the web. Female Student: what if I bought it from a friend? Teacher: you need to come see me. Female Student: are we doing CPR? Teacher: we are waiting for information on that. I am hoping we will Any questions about the CHEM, skill builder? Then, come and see me and we will work it out We talked about thermodynamics and other things. Lets go through them one by one Page 2 of 2

3 Internal energy, E E cannot be measured directly, but we can measure delta e, or the change. That is final minus initial. The IE, of a system, can be changed in 2 ways. 1. Add heat to the system, with a q, or generic heat, or remove heat from a system. 2. System does work; w, or work is done on a system. Know that q and w are not state functions. Using plus (+) or minus ( ) helps convey information. So let s look at sign conventions for q and w. If, q+, then heat is added to system, but if q-, then heat is removed from a system. Then, w+ is work is done on the system by the surrounding, but if w-, then work is done by the system to the surrounding. So E (i) and add heat to the system and do work on the system then we end up with E (f). There (Example on board.) is the formula. Delta E has a sign convention. E+ energy has been absorbed by the system. E -, energy is released from the system. If 1200 J of heat are removed from the system and system does 800 J of work then: (a) what is delta E for the system? Delta E is q + w, then delta E = -1200J 800J = J (b) for the surrounding delta E = J You can start with problem 72, which deals with E. You don t have to do BOPs in order, but label well. Page 3 of 3

4 Work in chemical reactions is due to changes in volume; we will only be considering gases. For example 1 mole of liquid (H2O) changing to 1 mole of gas (H2O) How much mass is one mol of water? 18g. Water as a gas still has 18g of gas. What is the volume or mils, density, of water do we have? Density of water is 1g/m. 1 mole of water as a gas, at STP, then temperature is 0^C, P is one atmosphere, that means it occupies 22.4L. That number you should memorize. What happens to the volume? The volume has expanded from 18 to 22+; in this situation, the system does work. The system, water, has pushed out against the surroundings. In this case, the sign is (-) negative, in this system. (Example on board.). PV = nrt Work done on gas equals -P (delta) V; calculate the work done on the following system done at 127C and 1 atm, given 4 moles of H2. (Example on board.) Here is the formula. Given 4 moles, here are 2 mol and we made 4 mol. Our reactants, in equation: 3 mol of gas going to 2 mol of gas. Consider STP, volume, etc. 3 mol 2 mol gas, then the surroundings are doing work on the system. The work is (+) positive. Page 4 of 4

5 Larger volume to a smaller volume here V(f) V(i) would seem to be negative, that is why we have the sign convention, because we know the work must be positive. (delta)ngas = ngas product ngas reactants, using our data 4 mol (2 mol and 4 mol) = 4 6; = 2. By the in front of the P, you can see this will be positive. The R, 8.314J/molK; the K that shows me what measurement for my temperature, with no degree symbol. (Example on board.). We know that work is equal to P delta V, then at constant T and P: (Example on board.) In some cases, no work is done. Examples of that would be: 1. Delta ngas = 0. W = -delta ngas RT. W=0 (Example on board.) using Cgraphite, etc. 2. Work depends on change in volume of system. That is w = -P delta V. If delta V=0 no change in volume w=0; if rxn is done in a closed container, constant V, then no work is done. Page 5 of 5

6 How is E measured? Using calorimeters. There are 2 types. 1. Bomb calorimeter rxn occurs at const V, it s a closed system. But pressure can build up. (Example on board.) Del E = q = w, = q + Here is the picture of one. There are ignition wires and we do combustion rxn. Heat is being released into the surrounding which is all this water. In the water there is a thermometer to measure the change in water. Process is for next time 2. Coffee cup calorimeter system can change volume and the rxn occurs at cont pressure. Quiz 3 (Example on board.). Open book, open notes and talk to your neighbor, but write your own work Page 6 of 6