CHEMISTRY COMMUNITY

Anna Yakura 2F

Use the half life equation for a reaction of first order!

Anna Yakura 2F

The way I did it is I determined which species were canceled out between the equations when added together. These should not be present in the overall reaction. This applies to both catalysts and intermediates. I didn't know the difference between the two but I think someone said under a different p...

Anna Yakura 2F

The "slow" vs "fast" indications are relative to the other elementary reactions. I think the professor will go over more of this in detail in the last two lectures but I think conceptually we just need to know that the slow step is the rate-determining step, and is going to contr...

Anna Yakura 2F

We have finished 7c as of friday's lecture! I'm pretty sure we'll finish everything else on wednesday.

Anna Yakura 2F

As others have said, it's really helpful to draw a quick image! Ultimately I think I just added the two numbers together (the positive versions) but it helps to know why you do that. Identify the activation energy on your curve, then the enthalpy of your reaction vs products. I don't think we've cov...

Anna Yakura 2F

The final last quarter for 14a felt a lot harder than the midterms personally. I will definetly be going to review sessions this week in preparation because the final will be cumulative.

Anna Yakura 2F

oh it seems like the solutions didn't upload, but I'm still struggling on how to start this in general.

Anna Yakura 2F

[img]file:///Users/annayakura/Desktop/Screen%20Shot%202021-03-01%20at%202.13.07%20PM.png[/img] [img]file:///Users/annayakura/Desktop/Screen%20Shot%202021-03-01%20at%202.14.37%20PM.png[/img] For this problem, I attached the original question and the solution from the solutions manual. How do we know ...

Anna Yakura 2F

The number of reactants does in some ways influence the order, if there are more reactants the order will probably be higher. That being said, some reactants are zero order, so they have no effect on the rate of the reaction (the professor explained this in the lecture by saying that those reactants...

Anna Yakura 2F

There are different ways to write the Nernst Equation so there are versions that already take the temperature and faraday constant into account. I would recommend making a chart or something of the different versions and when to use them (I know are different versions for log Q vs ln Q as well), or ...

Anna Yakura 2F

I think the order just tells the relationship between the concentration of reactants and the rate, and gives insight on how they influence each other. If a reactant is first order, you know that when you multiply that concentration by x, the rate is also multiplied by x (like the example seen in lec...

Anna Yakura 2F

I realize this is a broad question but can anyone give me tips on how to approach the problems in this section? I feel like the lecture didn't cover electrolysis too much in depth so is there anything I need to keep in mind when solving these?

Anna Yakura 2F

Some reactants can also have zeroth order, I think he mentioned briefly in the lecture that some reactants don't impact the rate at all because they are not involved in the "slow reaction." I was a little confused on this but because not all reactants influence the rate (n=0), reactions th...

Anna Yakura 2F

I'm planning on taking chem14c, ls7c, ls23L, and an easy GE if I find one!

Anna Yakura 2F

An intensive property means it does not rely on how much of the "thing" there is. I think of it kind of like molarity of a solution-- if you have 1.00 M solution, and gain more of it, the molarity hasn't changed, even though the amount of solution increased.

Anna Yakura 2F

Oh that's really cute! I always get confused with these types of things so this is helpful, thank you!

Anna Yakura 2F

Last quarter for 14A the UAs even had extra(?) UA sessions and a busier session schedule so kids could review for the final exam. These sessions were organized by topic so it was really helpful! I recommend going to these because you can get different types of questions that are not in the textbook....

Anna Yakura 2F

I completely understand what you mean, in fact I ask my parents not to ask how exams went until after I get my results LOL. Personally, I would try my best not to think about it. Immerse yourself in other classes for a bit, watch shows you like!

Anna Yakura 2F

^^ I agree, I wouldn't worry about it much, I just think you need to be able to apply the concepts if given a biological compound or example. I don't recall there being specific examples given in lecture

Anna Yakura 2F

Hello, I am also very nervous but here are some things I'm doing to help myself feel more prepared for the test! 1.) Of course, workin on sapling and tb problems, but also making note of what TYPES of questions there are (how they ask the question). Often times the question itself seems very dauntin...

Anna Yakura 2F

He didn't specify how many questions but he did say there were 8 point questions and 4 point questions. The 8 point questions have 4 point partial credit answers. Also there are two bonus questions! There's a very thorough explanation of the concept covered/ exam logistics on his website (and linked...

Anna Yakura 2F

Hello, for part b and c of this question, it asks (b) the melting of 1.00 mol C2H5OH(s) at its melting point; (c) the freezing of 1.00 mol C2H5OH(l) at its freezing point. These two are calculated in the exact same way but I was wondering if there are any conceptual differences I should be aware of?...

Anna Yakura 2F

Hello, did anybody else have issues with this problem? I set up my equation exactly like the solution manual but for some reason I am getting -2469.497 J/mol, which is not the right answer.

Anna Yakura 2F

Hello! The units are important for this one, use the one with units that make sense with what you're working with. Typically you'll use 8.314 J/mol.K when you're trying to find energy or work (bc of the Joules!), and the 0.0821 L.atm/mol with the PV=nRT equation and the like.

Anna Yakura 2F

I've been confused with this as well!

Anna Yakura 2F

Hello, are you allowed to assume that temperature is 298K if the question does not specify? For example, on 4D.7 on the outlines, it didn't state the temperature but when I assumed 298K, I got the right answer. When am I allowed to do this?

Anna Yakura 2F

The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113 8C to 22.799 8C. The calorimeter assembly is known to have a total heat capacity (calorimeter co...

Anna Yakura 2F

I'm pretty sure they both mean change in internal energy! Just be able to recognize both.

Anna Yakura 2F

Work is positive when the system is gaining energy, or when work is being done on it (for example, somebody pumping air into a bike tire). If a system is doing the work, work is negative because the system is losing energy to get work done.

Anna Yakura 2F

I'm just beginning to really start study thermodynamics (I've been keeping up with lectures but put the textbook questions aside to study for other midterms) and I'm confused on when to use what equation. I understand that you're supposed to look at the problem and see what variables you know, etc, ...

Anna Yakura 2F

I wouldn't worry too much about it, since a lot of people are having the same issue and chemistry community is meant to be easy points. I'm sure they will update it! As long as you're doing your 5 post a week I think you're good.

Anna Yakura 2F

Yes, I'm pretty sure resonance structures have more degeneracy, because there are more "possible states." That's a nice connection to 14a!

Anna Yakura 2F

What I do is I do the textbook problems (the ones on the outlines) after each lecture (the problems pertaining to what I learned that way). That way I can do the problems while they are fresh in my mind. I also recommend the UA worksheets, even if you can't go to the live sessions, to complete the w...

Anna Yakura 2F

I'm currently taking chem 14bl with Professor Casey, and I think the work is definetly manageable! The lab activities are done within the designated lab time, so the only weekly homework you have are lab reports (which have taken me 2 hours max? probably?) and optional practice sets/quizzes (which o...

Anna Yakura 2F

Personally it was a little harder than I anticipated. I did all of the textbook problems (from the outlines) at least twice and went through most of the UA worksheets, but for some reason when it came to the test questions I didn't get them as easily. Could definetly be my test anxiety though.

Anna Yakura 2F

I know the difference physically between the constant pressure calorimeter and the constant volume calorimeter, but am now sure how this affects the problem-solving process. Is there a difference is how I should approach these problems?

Anna Yakura 2F

Anna Yang 1A wrote:Does anyone know how to download lockdown browser or if there is a specific link we need for it?

The Respondus lockdown browser download link is on the CCLE website under Site Info! Should be near the very bottom of the page.

Anna Yakura 2F

The testing schedule is on his website (I think somebody linked it?), and the midterm will be 50 minutes. You need a lockdown browser called Respondus, the link to download it is on the CCLE website under Site Info (it is near the very bottom of the page). On the day of your midterm you need to log ...

Anna Yakura 2F

I think its similar to the qsys and qsurr thing he talked about in lecture today. An exothermic reaction has a negative delta H, yes, because heat is given off. But because the system is losing that heat, the surrounding is gaining it.

Anna Yakura 2F

For these problems, it helps to draw out the structures of each molecule: H2O is two H-O bonds. It also helps to explicitly write out which bonds to break, and which to form.

Anna Yakura 2F

LL14B21, an easy way to remember it is that it is the professor's initials (LL), the class (14B), and the year (21).

Anna Yakura 2F

Does anybody know when exactly we need to use this equation? I haven't encountered it in any of the textbook problems.

Anna Yakura 2F

It would be a strong base! You can think of it as a dial: if there are less acidic properties, it must have more basic properties, and be a stronger base.

Anna Yakura 2F

Definitely outlines 1, 2, and probably part of 3 will be tested. Around a week prior to the exam he usually sends an email with clear cutoffs on what will be tested (this will probably be available as an announcement on his website too).

Anna Yakura 2F

I was also confused on that! I think it applies to water because it is neutral (so [H3O+] and [OH-] concentrations should be equal).

Anna Yakura 2F

For the textbook question 6E.3, the solution manual states that when K(a1) is larger than K(a2), the second ionization is ignored. What does this mean, exactly, and is this always applicable to multi-step reactions? Thank you.

Anna Yakura 2F

805432537 wrote:How do I see that someone has replied to my question or answer. Do I have to continuously check? I did not use Chemistry community last quarter so I am very confused. Thank you!

For reference, this is a quote and you should get a notification for this.

Anna Yakura 2F

You will get a notification on the site if somebody quotes you in a reply. However, because many people don't quote, you can track your posts through the "Quick Links" on the top left, where it says "Your Posts." This is how I check if somebody has replied.

Anna Yakura 2F

Calculate the pH, pOH, and percentage protonation of solute in each of the following aqueous solutions: (a) 0.057 m NH3(aq) How do I approach this question? I have already set up my icebox but because the problem doesn't indicate a Kb number, I don't know what to set it equal to. In the solutions ma...

Anna Yakura 2F

In this problem and the pictures attached to it, you can see that on the right picture, there is more formation of X (product). The question basically asks what would increase the K value (more product compared to reactant). While adding X atoms, decreasing volume, and adding a catalyst may put the ...

Anna Yakura 2F

I usually go for animated films for comfort (like ghibli movies)! Also Kung Fu Panda.

Anna Yakura 2F

Hi! I've heard many people had issues with this but I would go to the CCLE website and access Sapling from there. For me, it immediately took me to a page that asked if I wanted to "use credit" or pay again. Choose the use credit option. If this doesn't work for you, you might want to swit...

Anna Yakura 2F

I use the textbook pdf (rather than the one connected to Sapling), and the equation is 2HD(g) = H2(g) + D2(g). This makes more sense because the equation is balanced. This is just a mistake on the textbook's part!

Anna Yakura 2F

In my textbook (I use the pdf version), the equation is 2HD(g) = H2(g) + D2(g), so that might be the issue! I would check the problem again. Your thought process seems correct.

Anna Yakura 2F

I'm a little confused at your question but when the reaction is at equilibrium, the concentrations of the reactants and products don't have the equal, it is the rate of the forward and reverse reactions that are equal. This is was contributes to the equilibrium constant (which is why K can be very l...

Anna Yakura 2F

Yes, just re-register! If you need an in-depth explanation on how to do that, you can check out Lavelle's website and there's a link to it on the top right-hand side. Even if you re-register, your posts will be saved because your account is connected to your UCLA ID.

Anna Yakura 2F

Can somebody help me approach this question? I know that the a) is exothermic and b) is endothermic but I'm not sure how to proceed from there. Thank you! 17. Determine the shift in equilibrium, if any, which will occur for the following reactions when the temperature is increased a) Photosynthesis:...

Anna Yakura 2F

Hello, I'm having trouble with this question in the chemical equilibrium pt.4 post-assessment. Predict the shift in equilibrium position, if any, which will occur when the temperature is increased. The hydrolysis of ATP: ATP (aq) + H2O (l) ⇌ ADP + PO42-(aq) delta H° = -30 kJ.mol-1 I know that the re...

Anna Yakura 2F

Hello all, what are some of your pre-final/test rituals?
Mine is going to bed super early but not being able to fall asleep and ending up sleeping two hours less than I usually do lol.
Also I wish everyone the best of luck, you'll all do great!

Anna Yakura 2F

Movies ad TV! Eating lots! Drawing and learning to crochet! Spending time with my cat! Facetiming friends!

Anna Yakura 2F

I would take another look at table 9C.1 and memorize what en, dien, and ox stand for. I think the things we should know would be its charge, coordination number, how to name them, what their formulas are. Hope this helped!

Anna Yakura 2F

You look at the resonance of an acid in terms of stability of the anion. When the anion has resonance, the charge is spread across more evenly across the molecule, which makes it more stable. The stable the anion, the stronger the acid. Compare this to an anion that doesn't have resonance -- the cha...

Anna Yakura 2F

Quantum was a huge unit so I'll probably go to a late quantum session, and review fundamentals and early quantum myself. I'll also prioritize the most recent stuff because I find it the hardest and don't understand it fully yet.

Anna Yakura 2F

^ when using the Lewis definition, its helpful to know that compounds with negative charge are bases (have extra electrons to give), and positive charges are acids. For neutral compounds, look at if the structure has a lone pair (can be a base) or is electron deficient in some way (can accept electr...

Anna Yakura 2F

Hello, are we required to memorize the ligand names for the final or will we be given a chart similar to the one in the textbook? Just wanted to check.

Anna Yakura 2F

Thank you guys! I just realized how silly my question is because I didn't even look at the first ligand ahah.

Anna Yakura 2F

Why is [Co(NH3)4(OH2)2] Br3 tetraamminediaquacobalt(III) bromide? I thought since aqua starts with A it would be named first (in the lecture today, Prof Lavelle said that the prefixes aren't taken into account when naming alphabetically). Just confused. Thanks!

Anna Yakura 2F

What I do is just count the regions of electron density, and correlate it to the hybrid orbitals that have that many things . For example, sp^3 has four regions of electron density (1 s, 3 p) are has a tetrahedral electron arrangement. That being said it might be best to review the lecture or the te...

Anna Yakura 2F

I think sp^3 was just common in the sapling because they like giving out molecules with tetrahedral arrangement of electrons, haha.

Anna Yakura 2F

Yes! You can think of it as 1.) there are more electrons that can interact with other electrons (of other molecules), and 2.) because there are more electrons, they experience a lower effective nuclear charge, and are farther away from the nucleus, and 3.) because they are farther away, they are mor...

Anna Yakura 2F

Hello! Personally I just try moving the bonds around, and seeing if they will work. Seeing if there are other alternatives for bonds (a single, instead of a double) could also provide resonance structures (but may not be the most stable/plausible structure). Often times in the textbook problems, the...

Anna Yakura 2F

From my understanding, finals are after week 10 so you do not have to keep attending classes while you're taking finals. That would be mean because you'll be learning new stuff lol. I don't know about the format or anything, I'm sure your professors will let you know (I'm assuming the formats will b...

Anna Yakura 2F

I'm pretty sure it's because TAs aren't decided for that section yet. I wouldn't worry about it and just enroll normally!

Anna Yakura 2F

Thank you everyone! I understand a lot better now, and the most recent lecture also clarifies some things. Thank you!

Anna Yakura 2F

I think the question will specify! At least with all the problems I've seen so far.

Anna Yakura 2F

I was under the impression that we all take it on the same day (not in our discussion sessions), especially because exam week is after week 10. I could be wrong though, and I'm sure Prof Lavelle will clarify in an email soon!

Anna Yakura 2F

Hello, I'm still having trouble visualizing what sigma and pi bonds are, and identifying them in Lewis Structures. In a sapling problem, I just counted the single bonds as a sigma bond, double bonds as 1 sigma 1 pi bond, and triple bonds as 1 sigma 2 pi bonds, and I got the right answer. Is this rea...

Anna Yakura 2F

Hello, I think there was a problem in the textbook like this. My impression was that you just write the VSEPR formula/shape in relation to the atom that the question asks about, and only take into account the atoms that they are directly bonded to. I hope this makes sense.

Anna Yakura 2F

I think you might just have to memorize it. Thankfully some of them are straightforward and you can narrow down your options by pictures the different planes.

Anna Yakura 2F

I don't know if I've done exceptionally well on the midterms, but I find that the textbook problems and UA worksheets are the best. I make sure to do the textbook problems as they come up in lecture (do the corresponding problems the day he lectures on them), so I'm on top of things and have time to...

Anna Yakura 2F

Hello! To determine if a neutral molecule is a Lewis acid or Lewis base, I generally start off by looking at whether the compound has a lone pair that it can share (making it a Lewis Base), of if it is electron deficient in any way (for example, Boron is often electron deficient), which will make it...

Anna Yakura 2F

I would expect around the same time as last time (so around Thursday)! Maybe even earlier if the prof and TAs don't have to go through each test like last time.

Anna Yakura 2F

The electronegative atom bonded to the H (that makes it partially positive) does not need any lone pairs!

Anna Yakura 2F

No need to know how to calculate them, just now how to identify them and how they contribute to the molecule.

Anna Yakura 2F

Hello, here's the process I use when trying to figure these out: 1.) Identify any cations or anions. Cations will be Lewis acid because they can accept and electron, while anions will be Lewis bases because they have an electron to give. 2.) For anything that's neutral, look for any electron deficie...

Anna Yakura 2F

When/where did we learn this exception? Just wondering bc this is the first time I heard of it oops

Anna Yakura 2F

Well, resonance structures are all plausible Lewis Structures. For example, if a molecule has two single bonds and one double bond, you can really put the double bond anywhere and those would be valid lewis structures. To pick the MOST plausible though, you have to take formal charges into account (...

Anna Yakura 2F

I just choose the bond type that the number is closest to, but in the case of an exam I would think the professor would give us a straightforward number.

Anna Yakura 2F

Hello, when an electron is delocalized, it is not associated with a single atom or bond. Lewis structures are not perfect representations of a molecule, and the real structure is a blend of the resonance structures, with the multiple bond character spread out across the molecule. I imagine it as the...

Anna Yakura 2F

NH3's shape will probably still be triagonal planar because there are three bonding regions. I think Professor Lavelle didn't go over it explicitly because we'll be going over it in future lectures. Also, if you recall in the lecture, he gave examples of if there are molecules with a certain number ...

Anna Yakura 2F

They are still being held!

Anna Yakura 2F

Angelica Soriano 1F wrote:
Nane Onanyan 1H wrote:Learning the choreo for "I Cant Stop Me" by twice B)

Hi fellow Once B)

I wish I could learn the choreo to "I Can't Stop Me" but Twice's choreos are too hard.

Hello fellow Onces :) Twice's choreos are also too hard for me :/

Anna Yakura 2F

Hello, I asked this question some time ago but I never got a clear answer so I thought I'd ask again.
With a radical, how do you know which atom has less than 8 electrons?

Anna Yakura 2F

Hello, I'm still confused on what exactly classifies as a dipole moment. I know that its influenced by charge differences between atoms (making partial negative and positive charges), but isn't this any molecule or compound that has two different elements bonded together? Practically everything is a...

Anna Yakura 2F

When counting for valence electrons in the p orbitals, I just disregard the d orbitals. For example, all group 13 elements have 3 valence electrons, group 14 has 4, etc. The way I think about it is when writing electron configurations, you always write s and p orbitals next to eachother (in increasi...

Anna Yakura 2F

Hello! For a neutral atom I usually look for lone pairs that can be shared (which will make it a Lewis Base!), or any electron deficient atom (which will make it a Lewis Acid, because it can take electrons). Electron deficient atoms can be group 13 atoms (a lot of the time Boron gives it away). Hope...

Anna Yakura 2F

Screen Shot 2020-11-09 at 4.06.13 PM.png Hello which would be the lower energy figure? I thought it was the one on the right because all the oxygens are 0, but the answer says its the left one. Can anybody explain why the left one has lower energy even though the right one has more atoms with a for...

Anna Yakura 2F

The way I interpreted it was that only Wednesday discussions were cancelled. Please correct me if I'm wrong though!

Anna Yakura 2F

The general rule of thumb is to put the least electronegative atom in the center. A lot of the time though, you can tell because the formula will tell you (ie. one of a certain element, four of another. you post the four atoms around the single one).

Anna Yakura 2F

This new show on crunchyroll started releasing episodes somewhat recently and it's called jujutsu kaisen! If you like action anime it has a lot of potential since it just started and it gained a lot of attention already and I think that it's worth the hype so far. I also just finished this one call...

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