CHEMISTRY COMMUNITY

gabbym

He had a slide on it at the end of class one day. It said like 83% or something, but I wasn't sure exactly what it was

gabbym

Hey guys, just out of curiosity, what was the average for the midterm?

gabbym

In a gas-phase equilibrium mixture of PCl5, PCl3, and Cl2 at 500. K, PPCl5 = 1.18 bar, PCl2 = 5.43 bar. What is the partial pressure of PCl3, given that K = 25 for the reaction PCl5(g) --> PCl3(g) + Cl2(g)? Hi, I don't understand why PCl3 = (25)*(1.18) / (5.43). I would have set PCl3 = (5.43)*(25) /...

gabbym

I can't find it either :(

gabbym

Has Lyndon posted his practice exam yet? I keep typing in "pork ramen" but I don't see anything posted :(

gabbym

During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 $C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1 $C. Assume ideal behavior. What is the change in entropy of the gas? For this...

gabbym

Write the half-reactions and the balanced equation for the cell reaction for each of the following galvanic cells: (a) Ni(s) / Ni2+(aq) // Ag+(aq) / Ag(s) In problems where you are given a cell diagram and asked to find the two half reactions and the balanced equation for the overall reaction, such ...

gabbym

Hey guys! I was wondering if anyone knew what name Lyndon is using for his practice exam. Please let me know if you hear anything :)

gabbym

Okay, thank you.

gabbym

Hey guys, when is Professor Lavelle holding office hours for week 10?

gabbym

Can someone explain to me how you know which compounds to use for the reduction reactions? For example, #14.13 Part D asks you to write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: Au+(aq) --> Au(s) + Au3+(aq) The...

gabbym

But I'm not understanding how you arrive at that conclusion for the half reactions. How do you know to separate the HCl into Cl- and H+? I would have just put that Cl2 goes to HCl and then H2 goes to HCl

gabbym

Can someone help me with #14.13 Part C? It asks you to write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: (c) Cl2(g) / H2(g) --> HCl(aq) I don't understand how they are getting the half reactions. Can someone expl...

gabbym

Wait I think I got it. You have to approach it like you're balancing a redox equation in basic solution.

gabbym

I need help with problem 14.1 part d in the sixth edition textbook. It asks you to write the half-reactions and the balanced equation for the cell reaction for each of the following galvanic cells: for the following cell diagram Pt(s) / O2(g) / H+(aq) // OH-(aq) / O2(g) / Pt(s) Can someone just walk...

gabbym

Would the entropy be different if the temperature isn't 298K? Or in other words, when using the delta S = nR ln (v2/v1) equation, does temperature matter?

gabbym

OOH that makes so much more sense! Thanks guys!

gabbym

Thank you for doing this for us! Greatly appreciated :)

gabbym

Thank you so much!

gabbym

Thanks!

gabbym

Here is a really interesting chemistry article about "gummy-like robots that could help prevent disease!"
https://www.sciencedaily.com/releases/2 ... 082155.htm

gabbym

Some TAs check if you're up to date with your posts at the end of each week and some don't. So if you get a little bit behind I wouldn't worry about it too much, just make sure that you do them eventually. There were a couple weeks where I got behind last quarter and I still ended up getting full po...

gabbym

Awesome advice! Thank you so much :)

gabbym

So there aren't going to be any questions regarding Gibb's Free Energy on the midterm? (Just double checking)

gabbym

Does anybody know if Lyndon has posted a practice midterm for his session on Monday? He usually announces what type of food he is going to label it under in lecture but he didn't this time

gabbym

This is most likely a silly question, but will we be given the standard enthalpies of formation on the midterm?

gabbym

Problem 8.59 says to use the data provided in Appendix 2A to calculate the standard reaction enthalpy for the reaction of pure nitric acid with hydrazine: 4 HNO3 + 5 N2H4 --> 7 N2 + 12 H2O I am trying to figure out why the standard enthalpy of formation for N2 is not used in calculating the answer. ...

gabbym

I think the only multiple choice questions will be in the form of true and false. For the discussion tests in 14A it was mostly a mixture of conceptual and calculation based questions. It won't be formatted like the post module assessments, but the questions will be similar.

gabbym

I'm pretty sure you would end up getting 0.232 - 4.64x + 23.2x^2 because when you cross multiply you also have to multiply the 23.2 and the x^2 together.

gabbym

Hey guys, I'm still a little confused on the 5% Rule. How do you know when to get rid of the x when you have something like x^2/0.20-x?

gabbym

Hey guys, do we have to memorize the acidity and basicity constants from the tables that were mentioned in the homework problems?

gabbym

15. At a certain temperature K = 4.0 for the esterification of ethanol and acetic acid: C2H5OH (aq) + CH3COOH (aq) ⇌ CH3COOC2H5 (aq) + H2O (l) If initially 2.0 moles of C2H5OH and 1.0 mole of CH3COOH are in a 1.0 L aqueous solution, what are the equilibrium concentrations of the organic molecules. C...

gabbym

16. 1.50 mol PCl5 is placed in a 500 ml reaction vessel and decomposes at 250°C to form PCl3 and Cl2. KC = 1.80, all substances are gases at 250°C. What is the composition of the equilibrium mixture? Can someone please work this question out for me and show me how you did it? I know how to do the IC...

gabbym

It's much cheaper to buy the textbook used off the UCLA Free & For Sale page on Facebook or some people will be giving out the PDF for free on there as well :)

gabbym

He doesn't post the lecture slides or Bruincast because he wants everyone to attend lecture as much as possible. If you miss a lecture all you can really do is ask a fellow student for the notes that you missed and take advantage of the other resources Lavelle provides.

gabbym

When is homework #1 due?

gabbym

Thanks!

gabbym

Are we going to be asked to find Ka and Kb on the test?

gabbym

Hey guys, here is just a little tip my PLF taught me to help me remember what bronsted bases are. Just remember that "Bases get H's

gabbym

Hey guys, here is a handy video to help you memorize VESPR shapes before tomorrow!
https://www.youtube.com/watch?v=P8d4WoXDLYM
(Note the following correction: "Sn of 5 is really cool, it's more than just trigonal bipyramidal")

gabbym

Thank you for taking the time to make this for us!

gabbym

Just check the email Lavelle sent today :)

gabbym

How much do we need to know about coordination compounds in regard to biological examples. Will there be questions regarding their biological importance on the test?

gabbym

I would just like to thank Professor Lavelle for being so kind and understanding when I was extremely sick and unable to go to lecture and having a difficult time keeping up with my classes. I was pleasantly surprised at how willing he was to work something out with me, as other professors in the pa...

gabbym

I stapled mine separately, but it probably doesn't matter that much!

gabbym

I was talking to a girl who took Chem 14A last spring and she said that Lavelle adds ten points at the end. I'm not sure if he adds ten points what you get on the final or to your total amount of points at the end though.

gabbym

Hey guys, I was unable to make it to my discussion the Wednesday before Thanksgiving, and I had a couple of questions regarding the upcoming test. I was wondering what kinds of questions were going to be asked regarding bond lengths and strengths. Is it just going to be mostly conceptual questions? ...

gabbym

"If Avogadro calls, tell him to leave his number." "OMG Did you hear that Oxygen and Magnesium are a couple?" "The name's bond, hydrogen bond." "That was sodium funny, I slapped my neon that one." "I don't trust atoms...I heard they make up everything.&qu...

gabbym

Did Lavelle decide if there is going to be lecture on the Wednesday before Thanksgiving?

gabbym

Ooh okay, thanks!

gabbym

In lecture last Friday, I think I heard Lavelle mention something about sapling learning? I've never heard him mention this before and I was wondering if anyone knew what he was talking about.

gabbym

When is the next text going to be?

gabbym

How can you determine if all the bond lengths are the same based off of a Lewis Structure?

gabbym

Approximately how long will it take for the midterm to be graded?

gabbym

Class Announcements is the place the look to see if Lavelle has posted something. If it is super important though, he will probably just mention it in lecture.

gabbym

Is there a list somewhere of the review sessions and practice midterms that are being offered by the UAs? Because I have class during the review sessions that Lavelle mentioned in class today :(

gabbym

I was wondering if the modules and assessments of the chem website were going to be updated since we've begun to cover new material. I find them really helpful :)

gabbym

At what velocity is an electron moving if it has a de Broglie wavelength of 7.0 × 10-11 m? Can someone help me with this problem?

gabbym

What do we need to know in regards to orbitals for the upcoming test? I'm pretty sure my TA told me that orbitals weren't going to be on the test, but then Lavelle went over them on Friday and said that they would be on the test.

gabbym

If an electron (mass 9.11 x 10-31 kg) has an associated wavelength of 7.28 x 10-9 m, what is its speed? Is your answer reasonable, why? Can someone help me with this problem? I think I am rearranging the equation wrong or something. I thought it should be v=h/m*wavelength, but I keep getting the wro...

gabbym

In the sixth edition solution manual, the solution for problem 1.43 uses the equation (deltap) * (deltax) = 1/2*h. Is the same as the (deltap) * (deltax) = h/4(3.14) equation that we were given in class?

gabbym

In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm. What is the energy per photon of light emitted? How many photons of infrared radiation does the lamp generate in 1.0 s? I was able to calculate the energy of photon per light emitted on my own,...

gabbym

Hey guys! My PLF taught me a tip for remembering the frequency equation. If you ever get stuck, just ask yourself, "What's new?" "Speed over lambda!"

gabbym

Hey guys! My PLF taught me a really cool mnemonic that I thought I would share with you. It goes like this: "Really Man I See U X Genius." R=radio waves, M=microwaves, I=Infrared, See=Visible Light, U=UV Light, and G=Gamma Rays.
I hope this helps!

gabbym

In a second experiment a shorter wavelength light source is used resulting in ejected electrons with a kinetic energy of 4.200 x 10-19 J. What is the energy of this incident light? What is the wavelength of this incident light? The first experiment gives you the work function 3.607 * 10^-19, with a ...

gabbym

This was so helpful, thank you!

gabbym

This was so helpful, thank you!

gabbym

Is writing in pen on the tests required? I am asking because it adds to my stress because I feel like everything is a mess. I realize that we are allowed to write out our work on scratch paper first and then transfer it over, but we are already pressed for time as it is. Can I just write in pencil a...

gabbym

Sweet

gabbym

I wasn't sure where to post this, but there's no test or exam during the week of Thanksgiving, right? There's only going to be one during the following week?

gabbym

If we don't carry every unit through our work, will we get marked down even if we have the correct units with the answer? For example if we didn't write down g/moles when converting grams to moles, will we get a point taken off?

gabbym

That was so helpful! Thanks!

gabbym

I am trying to figure out why the solutions manual put 50.0 x 10^-3 divided by (105.99)(0.07967) for part c of problem G5. I was trying to set it up like the previous parts a and b, with the desired amount of moles on top divided by the molarity of sodium bicarbonate and the times the molar ratio. F...

gabbym

What basic conversions do we need to know in preparation for the test next week? Besides millimeters to liters.

gabbym

In example H1 from the Fundamentals H section of the seventh edition, you are asked to write and balance the chemical equation for the combustion of liquid hexane, C6H14, to gaseous carbon dioxide gas and gaseous water. I understand that the liquid hexane needs to react with something in order for i...

gabbym

Example H1 under Fundamentals H in the seventh edition of the textbook asks you to write and balance the chemical equation for the combustion of liquid hexane, C6H14, to gaseous carbon dioxide gas and gaseous water. While I know of the top of my head that carbon dioxide is CO2, and that water would ...

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