CHEMISTRY COMMUNITY

Tikva Cohen 1K

as long as you've posted 50 times by the end of the quarter you get full points but you can't get extra credit. you don't even have to worry about 5 per week just 50 for the quarter.

Tikva Cohen 1K

It's definitely just if you have 50 total for the quarter cause my points are already on myucla and the quarter isn't over but I have 50/50 so yeah its like last quarter.

Tikva Cohen 1K

definitely looove poke/sushi!

Tikva Cohen 1K

favorable or stable or spontaneous all imply the same thing: deltaG < 0 (negative)

Tikva Cohen 1K

that's normally the case, but don't make that assumption because you don't wanna mess yourself up. always use whichever one cancels all the right units out.

Tikva Cohen 1K

As a response to my own post, I am taking LS7A, Ling 1, and Engcomp 3D. Not even close to my ideal schedule, but with my morning pass and UCLA's lack of uploading enough classes for all students - this will have to do. Linguistics fills a GE and the Engcomp fills the Writing I requirement. I wanted...

Tikva Cohen 1K

The following website has a great walkthrough and example with solution! https://socratic.org/questions/how-do-you-calculate-the-oxidation-number-of-an-element-in-a-compound thanks for this helpful link! i'm a bit confused on oxidation numbers as well.. also, this may be a dumb question, but what e...

Tikva Cohen 1K

literally watched both the new electro lectures right after and doing work but honestly feel good bc im being productive. gonna have a yummy dinner to reward myself tonight :)

Tikva Cohen 1K

I have been noticing this as well, and really struggling to do some of the focus problems without viewing the answer key/explanation, so I really hope Lavelle's are a bit more simple.

Tikva Cohen 1K

n and m simply refer to the molar coefficients, so it would be 4(Cl2) and 2(CCL4) because of their coefficients.

Tikva Cohen 1K

reversible implies isothermal, however an irreversible reaction can also be isothermal because it just means there's constant temp. therefore, isothermal does not imply reversibility

Tikva Cohen 1K

i think I'm going to take chem14c, ls7a, and spanish 3 but it depends how they fill up. i am also considering 14bl and stats 13

Tikva Cohen 1K

Yes, usually the week of/before a midterm they all do review. I highly recommend attending as many as possible!

Tikva Cohen 1K

Does anyone know if Midterm 2 will cover all the material from this quarter we have learned so far? Or only cover what we have learned since Midterm 1? I'm almost positive it's only what we've learned since midterm 1 since thats how Lavelle did it last quarter. So it should be all thermo stuff. He ...

Tikva Cohen 1K

If the system is being compressed, then there is work being done ON the system and the work is positive. This makes sense because the change in volume is negative. If the system is being expanded, then there is work being done BY the system and the work is negative. This makes sense because the cha...

Tikva Cohen 1K

if q<k, that means there is an excess of reactants (bc q=p/r) and so it will be spontaneous in the forward direction. (when there's extra reactants they are used to form products.) if q>k it's the opposite, there's an excess of products so it's spontaneous in the reverse direction. if q=k, it's at e...

Tikva Cohen 1K

I believe they are given to us on the equation sheet, so I don't think you need to memorize them, but just conceptually understand how we get them and when to use them.

Tikva Cohen 1K

I thought I understood this problem but keep trying and getting it incorrect. I've been looking at these explanations so hopefully after trying again i'll get it correct! thanks!

Tikva Cohen 1K

if you remember, the problem is asking to "Classify the phase changes by the signs of the system's ΔH and ΔS" and then you categorize the phase changes whether they're positive/negative. I thought I understood this ( I definitely understand the endo vs exothermic but not the deltaS) but ca...

Tikva Cohen 1K

I was confused on this as well until I came on chem community! I don't remember learning about that deltaG equation yet. Thanks for the helpful responses, I understand now.

Tikva Cohen 1K

Yes, I think they are. I think going over the textbook problems is great too because Lavelle pulls many exam questions from the textbook, but the Sapling is great practice and reading over the final solutions on there is helpful as well.

Tikva Cohen 1K

I think the best thing for me is just practice. So workshops and step up sessions were great for extra practice, but also just going over the outlines and doing all the homework problems over again. Also just focusing on specific equations or topics that i know I need more help on.

Tikva Cohen 1K

I've heard it's pretty hard to get into 14BL as a freshman, so I think I'm going to take 14C in the spring and BL either summer or next year sometime. Do you guys think that's fine to do? I'm planning on doing the same thing as you! I also don't know how I feel about taking two chem courses at once...

Tikva Cohen 1K

SelenaDahabreh1D wrote:
Tikva Cohen 1K wrote:wait so even if we want to review our midterm we can go to any TA?

Yes, I believe so. In Chem 14A, I think we were also able to go to any TAs office hours to review our midterm.

Okay amazing thank you!

Tikva Cohen 1K

I've heard it's pretty hard to get into 14BL as a freshman, so I think I'm going to take 14C in the spring and BL either summer or next year sometime. Do you guys think that's fine to do?

Tikva Cohen 1K

Madison Wong 3H wrote:I think it would be generally helpful to make distinctions between types of calorimeters and how measurements from calorimeters can help in various calculations.

What are the different types/uses of calorimeters? I'm still confused on them.

Tikva Cohen 1K

I honestly feel the same way, I studied for a week and did terrible. Should I consider dropping? it would be a good idea to estimate the final grade by using the standard grade curve first. P/F is also an option Does this class usually curve the final grade? No he doesn't curve, but sometimes he'll...

Tikva Cohen 1K

wait so even if we want to review our midterm we can go to any TA?

Tikva Cohen 1K

For the step up sessions, do UAs just give worksheets to work on for the duration of the session or do they also go over each problem? In step-up sessions, the UA will screenshare a worksheet and work through it with the students as you go along and explain each step. for workshops, the UA gives yo...

Tikva Cohen 1K

i would definitely agree and say just continuously working through problems (whether that be textbook, sapling, UA stepup sessions and workshops) is the best way to study and help yourself in this class. it ends up being a lot of work and takes time to understand everything but that's what works for...

Tikva Cohen 1K

A UA mentioned yesterday that the integral equation was just shown in lecture for us to understand how the work equation was derived, but that we don't actual perform integrals in this class.

Tikva Cohen 1K

Definitely agree with everything said, but I do feel a bit overwhelmed as well, since chem is not my only class. My advice would be to outline each day which section you want to work on and go over textbook problems for that topic, and then ask questions on chem community when something is confusing...

Tikva Cohen 1K

To add on, they update it and also I think as long as you just post 50 times total by the end of 14b you get all full points.

Tikva Cohen 1K

there isn't really a good solution to this problem other than just trying to be more careful and doubling checking over all of your work. I know this is hard during a time crunch but my advice would just be to make sure you look over every step before moving on. Hope this helps a bit! Good luck

Tikva Cohen 1K

Yes it's simple as that! a for acid and b for base just to differentiate between the two

Tikva Cohen 1K

Yes they will all be multiple choice. Lavelle might do a review lecture, or he has office hours and also all the UA's have review sessions and TA's have office hours as well.

Tikva Cohen 1K

Yes they will all be multiple choice. Lavelle might do a review lecture, or he has office hours and also all the UA's have review sessions and TA's have office hours as well.

Tikva Cohen 1K

If the product concentrations are given/stated in the problem, then you can include them in your ICE table for the initial concentrations! However, a lot of the time, your product concentrations will be 0. A lot of the problems I have seen have given me an initial concentration for the reactant(s) ...

Tikva Cohen 1K

so basically as long as we have 100 posts by the end of the quarter we get our points..?

Tikva Cohen 1K

how do you know when to put 0 for the initial concentration of the product or when to write in a concentration that is given? I thought it was always 0 since the reaction doesn't occur yet but sometimes you put in a concentration... not sure if this makes sense but thank you!

Tikva Cohen 1K

Hello! To solve this you must multiply the equilibrium constants of the two constituent equations, which would be the equations in which HI and NH3 are the products. You'll have to make some conversions though, because you'll notice that the primary equation is not identical to the given equations....

Tikva Cohen 1K

Consider the reaction of NH3 and I2 to give N2 and HI. 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g) Using two or more of the given equations, determine the equilibrium constant, , for the reaction of NH3 with I2. H2(g)+I2(g)↽−−⇀2HI(g)I2(g)↽−−⇀2I(g)N2(g)+3H2(g)↽−−⇀2NH3(g)H2(g)+Cl2(g)↽−−⇀2HCl(g)a=160b=2.1×10−3c=3.6...

Tikva Cohen 1K

hmm I haven't noticed this happening to me, but maybe if you try to download the pdf to your computer or google drive it might realign? not sure, sorry about that!

Tikva Cohen 1K

Accoding to the ideal gas law, PV=nRT. If we divide both sides with V, we could have the equation for pressure: P=(nRT)/V Because n (in moles) divided by volume V(in liters) would result in concentration (in moles per liter), we could substitute n/V in the equation with concentration. Therefore, P ...

Tikva Cohen 1K

It has to be in Kelvin in order to cancel out the units, but if you're given something else you can just convert it.

Tikva Cohen 1K

what they said^^ and also Lavelle will confirm what's on the midterm as we get closer to it too

Tikva Cohen 1K

it depends on the units you have and are using. You want to use whichever ones will work for yourproblem and cancel out

Tikva Cohen 1K

to add on to this, how do you know when to put 0 for the intital concentration of the product versus a concentration that is given? I thought i t was always 0 since the reaction doesn't occur yet but sometimes you put in a concentration...

Tikva Cohen 1K

I have tried to complete this problem with multiple attempts but cannot figure out how to do it. Would someone be able to explain? Thanks! At equilibrium, the concentrations in this system were found to be [N2]=[O2]=0.100 M and [NO]=0.400 M. N2(g)+O2(g)↽−−⇀2NO(g) If more NO is added, bringing its co...

Tikva Cohen 1K

apurva-3E wrote:Did you purchase the multiterm access? If not, all I had to do was check "use $72 credit"

I'm not sure, but I can't even get to the option to use my credit...

Tikva Cohen 1K

I am still getting the error when I try to go on sapling for 14b and cannot get the option to use my credit towards this quarter. i have gone to the site thru CCLE and still no luck. Anyone know how to fix this?

Tikva Cohen 1K

i had the same question! I'm confused on how to determine this, and the textbook's answer is not very helpful at least to me

Tikva Cohen 1K

The reasoning that you used is incorrect because that is for acids with no oxygen attached to it, in other words for acids like HI, HBr, or HCl. However, in oxoacids with a Lewis structure of something like R-O-H, with R being another element like Cl or Br, the H is bonded to the oxygen, not R. The...

Tikva Cohen 1K

ranking the the oxoacids according to acid strength... the answer is HClO>HBrO>HIO I thought the most acidic would be HIO and then HBrO since the bonds are longer and we learned that longer/weaker bonds = more acidic because they'll more easily lose a proton. Can someone explain why these are differ...

Tikva Cohen 1K

Yeah I've had some issues with the casting this week even when using the VPN, I don't know what the issue is but if you come back to it after a while it usually works. Just trial and error unfortunately.

Tikva Cohen 1K

Does anyone have a good set of practice problems I could use to study the final or like a compilation of homework problems something like that? I've been going through textbook problems but just wondering if anyone else has more resources I could use. Thanks

Tikva Cohen 1K

Yeah, unfortunately I haven't been able to find anywhere that our grade is calculated for us which is weird, but basically like everyone else said you just add all your points up and put it out of the totals and that'll give it to you

Tikva Cohen 1K

I'm okay, thanks for asking! Actually feel pretty good about most chem material, just a little stressed with finals coming up and especially with multiple classes at once. Hopefully it's al be good!

Tikva Cohen 1K

Adding the the responses, when things are ligands, they have different/specific names, so ammonia turns into ammine. it's the same thing! just uses a different name when it's a ligand

Tikva Cohen 1K

It seems like it based on what he said and wrote in the lecture!

Tikva Cohen 1K

thanks!! I have mine tomorrow so I'm still studying and we'll see how it goes, but definitely going to take a little break hang out with friends stuff like that lol

Tikva Cohen 1K

It's definitely possible, but I think "Online-Recorded' for most classes means it' a zoom online but will also be recorded. This is how my LS30A teacher does it so if you miss a zoom you can go back and watch the recordings.

Tikva Cohen 1K

I understood the word important as just another way of saying which of the following molecules exhibit dipole-dipole interactions or like you said if the dipole-dipole interactions are present. Okay awesome, thank you! I realized also after I looked at the solution that is exactly what it's asking,...

Tikva Cohen 1K

Definitely doing textbook problems helps, I've heard that's what he bases a lot of the exam on. Even if you've done all the problems, you can go back and do them again! Also reviewing the outline and making sure you understand everything on there. I also like to watch youtube videos to clarify thing...

Tikva Cohen 1K

They definitely are not testing us on this for the midterm, my TA confirmed all formulas will be given to us. It is helpful to know, but we will be learning this later in the quarter so I wouldn't worry about it until we get there. Good luck!

Tikva Cohen 1K

I believe so, I think either my TA confirmed this or maybe a UA I'm not sure, but also we won't have to know any other exceptions besides these two for the midterm! :)

Tikva Cohen 1K

To add to that, Oxygen is the most electronegative in this scenario and in a lot of molecules, so a lot of times that's where you want the negative charge.

Tikva Cohen 1K

oh also if its a diatomic molecule like in this case CL2 it's always nonpolar because they both pull the same amount in opposite directions and the vectors cancel

Tikva Cohen 1K

usually it's by looking at the electronegativity of each elements. whichever is more electronegative will pull towards itself, and then you draw the vectors accordingly. then add them to see which direction they go in. if they all cancel out, it would be nonpolar, if they don't cancel, it's polar

Tikva Cohen 1K

The question is "3F.3 For which of the following molecules will dipole–dipole interactions be important: (a) CH4; (b) CH3Cl; (c) CH2Cl2; (d) CHCl3;
(e) CCl4?"

what does the word important mean in this case, just when will dipole-dipole forces be present?

Tikva Cohen 1K

Hi, "Degenerate" in our class so far has been used to refer to orbitals, and it means that they have the same energy. Not every orbital has the same energy but in some cases, like in single-electron atoms, different subshells of the same principal energy level are degenerate (eg, the 2s a...

Tikva Cohen 1K

Some of the homework questions in this section expect us to draw Lewis structures or ions from the written out name of the molecule. For example, On the basis of the expected charges of the monatomic ions, draw the formula unit of each of the following compounds using Lewis symbols: (a) thallium(II...

Tikva Cohen 1K

My TA mentioned this in discussion but I am a little confused. What does degenerate mean and what does it refer to (i.e. electrons, orbitals, or other?). And where/how are these found? Hope this question makes sense thans!

Tikva Cohen 1K

Some of the homework questions in this section expect us to draw Lewis structures or ions from the written out name of the molecule. For example, On the basis of the expected charges of the monatomic ions, draw the formula unit of each of the following compounds using Lewis symbols: (a) thallium(III...

Tikva Cohen 1K

Does anyone have a good way to memorize the trends in the periodic table?

Tikva Cohen 1K

My TA said they were definitely waiting until everyone took the exam, so that would be at least the end of today, but he didn't say how soon after so I don't think anyone really knows.

Tikva Cohen 1K

You are suppose to use E=hv with protons because they do not have mass thus the m is missing from the equation. While for E=1/2mv^2 is used for electrons or anything else that has mass and most of the time in the problem they either give you the velocity or the mass which is a huge giveaway to whic...

Tikva Cohen 1K

I only remember seeing this is one homework problem and it was one of the ones my TA went over in class and he never did the particle in a box thing or talked about it so I’m hoping we don’t really need to know it for the midterm.

Tikva Cohen 1K

If you have access to the Solutions Manual, it was helpful to me to look over and to work through the problem using their solution, and then after I figured out what to do, I re-tried the problem later on without the solutions and was able to do it on my own. It shows that you use the speed of light...

Tikva Cohen 1K

The uncertainty equation is given as P(change)*X(change) is greater than or equal to h/4pi. Due to the greater than or equal to, any value for position(x), momentum(p), velocity(v), or mass(m) that satifies the equation given the other variables, will already be the minimum possible value for that ...

Tikva Cohen 1K

I’m not sure if we ever learned or if there is a difference between the minimum and maximum uncertainty in Heisenberg’s equation. Is there a difference, and if so is there something different you do to find them using the equation?

Tikva Cohen 1K

Darlene Lien 1B wrote:Hi, 3.37 x 10^-19 J was the energy you get from part a. Hope this helps.

Omg duhhh I’m so dumb thank you!! I was rlly struggling where it came from but I’m just oblivious lol

Tikva Cohen 1K

Pranav Daggubati 1A wrote:This is due to the typesetting feature they use which can be really inefficient in cases with long page-lengths

Is there any solution to this?

Tikva Cohen 1K

Hi, I've been noticing my Sapling textbook link sometimes does not give all the information in the questions, like it has numbers or equations missing that are essential to the problem so I have to reload the page multiple times until it shows up, or look up the question on Chem Community to find it...

Tikva Cohen 1K

The 32W is given in the problem: 1B.9 A lamp rated at 32W(1W=1J⋅s^−1) emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval? ohhh what okay then my textbook is messed up that makes so muc...

Tikva Cohen 1K

Where does the 32W come from in this problem?? I'm confused? The 32W is given in the problem: 1B.9 A lamp rated at 32W(1W=1J⋅s^−1) emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval? o...

Tikva Cohen 1K

Where does the 32W come from in this problem?? I'm confused?

Tikva Cohen 1K

I understand how to do each part, but in part (b), you have to change the units from Joules to atoms, in order to get the energy in Joules. In the solutions manual, it multiplies by 3.37*10^-19 Joules per atom, but this is not given in the problem and I don't see it on the formula sheet. Is this spe...

Tikva Cohen 1K

In multiple lectures Prof Lavelle essentially said these are the same things as well as Line spectrums. They can mean incoming versus outgoing or small subtle differences like that but they're all really the same thing and have the same values.

Tikva Cohen 1K

Prof Lavelle in his email said Amazon, but I also don't think it's necessary if you have another device to use!

Tikva Cohen 1K

My TA said it would be multiple choice as well. He didn't know how many questions but said it would be manageable for the 50 discussion time.

Tikva Cohen 1K

Okay, thanks so much for looking!

Tikva Cohen 1K

@Lindsey Su You would have E, the energy per photon from the previous part, so dividing the total energy 3.08x10^-7, by the energy per photon should give you the number of photons. If each photon only ejects one electron, then this should be equal to the number of electrons that were ejected. I kee...

Tikva Cohen 1K

And similarly, are our TA's going over all the information and things we need, as well as like info on studying or are we kind of just on our own to figure it out?

Tikva Cohen 1K

Not sure if someone asked this already but is there a group me for discussion 2I! Thanks!

Tikva Cohen 1K

I was wondering the same thing about the step-up sessions, too! Thanks so much.
I think the different UA's have their own stuff though so even thought going to ones hosted by the same UA is repetitive, going to other UA sessions will help more!

Tikva Cohen 1K

he didn't tell us specifically to do those ones like the other modules but since they're on his website I'm sure they would be very helpful otherwise he wouldn't have them there. And there's no harm in checking them out!

Tikva Cohen 1K

I believe the main difference is that classical mechanics describes larger items or objects we can physically see and hold why quantum pertains to microscopic objects where our eyes can't actually see them. So if that's the case then you're most likely right because chemistry usually deals with micr...

Tikva Cohen 1K

So a wavelength is the literal length of the wave, or how long it actually is, where the frequency is how many waves pass a certain point in a certain amount of time. Also, the two terms are directly related, so waves with higher frequencies have shorter wavelengths while those with lower frequencie...

Tikva Cohen 1K

So far no one has told us we need to memorize them. Also, in one of Lavelle's lectures he mentioned that most things you need should be given to you in the problem, and the point of this class is to be able to use what is given to problem solve, not just memorize a bunch of things, so I think you're...

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