CHEMISTRY COMMUNITY

Lisa Wang 3B

I read in the rules/index somewhere on chemistry community this trick, and it has helped me a lot. 1) Use the search bar WITHOUT entering in anything and click search. This will take you to a different looking page. 2) On the second item on this page, you will see "search by author" 3) En...

Lisa Wang 3B

I took extensive notes on how to graph the first, second, and zeroth order reactions and their respective y-intercepts. This helped me memorize the equations instead of relying on the equation sheet.

Lisa Wang 3B

Here are my objectives
1. see all endorsed posts
2. see all chem_mod replies

Is there a trick/filter/place where I can do that on chem community?

Lisa Wang 3B

Dorming sounds really nice right now! These days spent inside my comfort zone are making me feel like a hermit crab. I do wonder how UCLA is going to accommodate two incoming classes coming for their three-year housing guarantee.

Lisa Wang 3B

The transferring of OH- and H3O+ ions, respectively, would bring about change in the pH and buffer solutions.

Lisa Wang 3B

the value of n is the electron transferred in the reaction. Typically, I look at the two equations after the electrons are on their respective sides (ready to be canceled out).

Lisa Wang 3B

Like the above answers, I don't think Professor Lavelle will tests us on third order reactions as it is not probable for it to happen. I also don't see its related equations so I will generally assume the ones that are essential are zeroth, first, and second order reactions.

Lisa Wang 3B

I see it on ccle, but I don't see it on myUCLA. Maybe it just takes time to update once in a while!

Lisa Wang 3B

I was told that it is conventional to have the aqueous elements closest to the salt bridge. Can anyone confirm this?

Lisa Wang 3B

for summer sessions, I think it is cost/unit and you have until June 18th to pay the enrollment fees.

Lisa Wang 3B

Janelle Gokim 3B wrote: If it were a dilution of the cathode side, it would decrease the cell potential because there is a smaller gap in the concentration difference.

Thanks so much for this explanation!

Lisa Wang 3B

for part b of 6.53, how would adding 100mL of pure water to the anode department (lower concentration) increase the cell potential? I thought dilution will only decrease the cell potential?

Lisa Wang 3B

Unlike the LS tests, we can't see our submitted test answers on our own part. TA's have access to it and would be able to help you!

Lisa Wang 3B

Like the others have said, the textbook outlines most of the concepts in its examples. Another student have told me that if you really understood a concept, then you would be able to cover up the numbers and explain the textbook's steps in words. Try doing that to test yourself!

Lisa Wang 3B

the principle is first notice which side is lacking an Oxygen or H+ ion. If it is oxygen that is needed, then add H2O. If it is H+ ions that is needed, add H+ ions. On the opposite side, you want to balance it out with the OPPOSITE item that you just added. Overall, think about it as if you're balan...

Lisa Wang 3B

JoshMoore2B wrote: So, favorable reactions are likely to be spontaneous, increase entropy, and increase stability.

Can you please explain why increase entropy and increase stability goes hand-in-hand? It kind of confuses me how something that can be more disordered but more stable at the same time.

Lisa Wang 3B

I believe you have to realize the direction in which the electrons are flowing, in which the electrons will be flowing from the anode to the cathode. By convention, also, anode is located on the left.

Lisa Wang 3B

As stated in the previous reply, an electrical potential is a measurement of the ability of a voltaic cell to produce an electric current. A cell potential is the potential difference between two half cells in an electrochemical cell. The maximum potential is the maximum voltage difference, which o...

Lisa Wang 3B

In Friday's lecture, Dr. Lavelle said that that day's lecture material revolves around E knot Cell, meaning that the cell is in standard conditions (pressure 1 atm, temperature at 298K (I would assume)). Next lecture we will be talking about E cell, not in standard conditions.

Lisa Wang 3B

Like the above have mentioned, the standard room temperature is usually 25 degrees and add that to 273 you get 298k

Lisa Wang 3B

I definitely would be taking BL if there are any more spots left! Hopefully the class won't stay closed

Lisa Wang 3B

Vivian Hoang 1H wrote:Yes, it is convention that anodes are always on the left and cathodes are on the right!

Thank you!

Lisa Wang 3B

Are Anodes always located on the left and cathodes on the right? (or is that just by convention)

Lisa Wang 3B

You're correct--- the Cp,m is just molar heat capacity at constant pressure. It means that the units will usually have a (mol^-1) and that we are looking not at a specific heat capacity anymore (which is just a regular C)

Lisa Wang 3B

Container A has a monoatomic ideal gas, which means it's going to be more disorderly than a diatomic one, as there's more molecules to bounce around and do their chaotic, molecule-y thing. Lemme know if you need clarification! Can you please explain why a monoatomic ideal gas is going to be more di...

Lisa Wang 3B

I recommend trying out the "Pizza rolls" worksheet on here. You can search it up, it has been downloaded many times.

Lisa Wang 3B

The small bags of silica gel you often see in a new shoe box are placed there to control humidity. Despite its name, silica gel is a solid. It is a chemically inert, highly porous, amorphous form of SiO2. Water vapor readily adsorbs onto the surface of silica gel, so it acts as a desiccant. Despite...

Lisa Wang 3B

The equation, when given the other components, can be used to find delta H, T, delta S, and K. In some circumstances, you can use n*delta H = q or delta G = -RTlnK in conjunction to help you.

Lisa Wang 3B

degeneracy should be the number of arrangements and so should be just simply counted.

Lisa Wang 3B

So for the flask example, there are two states that a molecule could be in: either on the left side of the flask, or the right side. Degeneracy is the number of ways of achieving a given energy state, so with one molecule in that flask, degeneracy is 2, because the molecule could be either on the l...

Lisa Wang 3B

you shouldn't worry about it! Just finish your remaining posts and your TA will update it for you for this week's.

Lisa Wang 3B

I remember learning to read the question carefully, and especially between the word "on" and "by". Work done on the system and work done by the system are signaling different signs.

Lisa Wang 3B

kind of unrelated--- does anyone know when the scores are typically released?

Lisa Wang 3B

I would recommend Mathew Tran's UA worksheets! They are posted in the forum in unanswered posts.

Lisa Wang 3B

Something to do before we take a midterm: exercise your mind and body.
I think for prof Lavelle's midterms, going through the learning objectives on the outlines really help.
For this particular midterm, I would say know whether left/right learning based on incr/decr P, V, and T with given delta H's

Lisa Wang 3B

kind of a side question, is 14BL usually offered in summer as well? If so, is it being offered in sess A or C?

Lisa Wang 3B

while we might not be always given ka values and kb values, we might encounter statements like "the pKa of [censored] is 3.04" and we can still figure the ka or kb value from that line of reasoning. But for this particular scenario, we would have to refer to the two charts for sure.

Lisa Wang 3B

I got that answer on the first try also, but I think it's because you must flip the sign of the product formation energy (the one on the right).

Lisa Wang 3B

How did ya'll work through this one? I'm having trouble figuring out where to start. For a certain reaction at constant pressure, ΔH=−15 kJ, and 22 kJ of expansion work is done on the system by compressing it into a smaller volume. What is ΔU for this process? Thanks in advance! H = U + (-PV ) sinc...

Lisa Wang 3B

Hi! it looks like the question said: "If the equilibrium composition is 0.495 mol?L21 Cl2 and 0.145 mol?L21 BrCl" so we can assume that the solution is already at equilibrium, and we only ICE tables if we know the initial concentration and would like to *get* to the equilibrium composition...

Lisa Wang 3B

so in class we learned that endothermic is a general intake of energy and the greatest intake of energy comes from breaking the weakest bonds and forming the strongest bonds. The opposite is for exothermic reactions.

Lisa Wang 3B

In lecture, Dr. Lavelle said that all other bond enthalpies are averages from many different molecules. Can someone please give me some examples of this point?

Lisa Wang 3B

so for a lot of the UA step-up sessions I'm seeing A + B (front back arrows) C. Do we usually assume that the concentrations/pressures are referring to not solids and liquids? Because otherwise say A (s) would not be factored into the computation, right?

Lisa Wang 3B

the second deprotonation means removing a proton again, in a subsequent reaction.

Lisa Wang 3B

A 0.305 mol sample of Xe(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 19.3 K. Calculate the amount of heat q required to bring about this temperature change, and find the corresponding total change in the inter...

Lisa Wang 3B

Like the others have said above, I also agree that outline 3 will be partially tested. I definitely think we will not be tested on outline 4.

Lisa Wang 3B

Hi! The concentration will remain unchanged because the proportionality equation would be ratio-wise balanced so that the nRT part are not affected.

Lisa Wang 3B

for this problem's part b, it looks like my answers do not match the answer at all. I got that delta T = (765J)/(0.82mol)(3/2R) = 74.8077K which then I add to the initial Temperature 298 K ---> 74.8077 + 298 = 372.807 K as the final temp delta H would be --- > H = U + nRT = 765 + (0.82)(8.314)(74.80...

Lisa Wang 3B

Nope, you can have unlimited tries!

Lisa Wang 3B

for 5.33, why wouldn't adding the catalyst not favor either X(g) or X2(g)? I thought a catalyst would always drive a reaction, it just doesn't change the concentration of the reactions nor products. Can someone also explain to me what the answer means to say in simpler language: "Also, the valu...

Lisa Wang 3B

1. Balance the equation: 2AsH3 (g) <--> 2As (s) + 3H2 (g) 2. Solve for the concentration of AsH3 and H2 by dividing the given molar amounts by 3L (you can disregard As in this problem because solids are not included when solving for Q) 3. Plug in the values of the concentrations into the reaction q...

Lisa Wang 3B

Yes, they will be during lecture time. It's not going to be the same as chem 14A, where we would have it during discussion.

Lisa Wang 3B

Hi everyone! I was having trouble figuring out this problem: You are studying the following unbalanced reaction at high temperatures: NH3 (g) ⇌ N2 (g) + H2 (g) In one of your experiments at 500 K the measured partial pressures are: NH3 0.887 bar H2 0.168 bar N2 0.0561 bar a) Determine the equilibri...

Lisa Wang 3B

Hi, 1. balance the equation ---> 2AsH3 equilibrium arrows 2As + 3H2 2. get the concentration by dividing by the volume 3. take consideration of the coefficients For my answer, I got 2.2553x10^-9, but that is because I rounded off a lot of the numbers. The correct answer should be C, to my guessing.

Lisa Wang 3B

for the matter of knowing the bond angle, it is only necessary that you know NH3 has a trigonal pyramidal shape and it Is going to have a bond angle less than 109.5, which fits here.

Lisa Wang 3B

I believe we only need to know that the more oxygens there is, the more acidic it will be in terms of oxyacids.

Lisa Wang 3B

I remember seeing a lot of pi bonds having this hybridization: 2p. In fact, every pi bond I've seen has that hybridization. Does anyone know why that is?

Lisa Wang 3B

The best way for me to cope is take a small nap, which always energizes me afterwards.

Lisa Wang 3B

When atoms are directly bonded (HCl or HBr), we look at bond length. When they are not, we look at electronegativity.

Lisa Wang 3B

Which sheet are you referring to? Can someone help me find it?

Lisa Wang 3B

think about the electronegativities instead of the lewis structure in this question. Since we know that Cl- is more electronegative, then it would make sense that in a tetrahedral arrangement, no matter where you put the Chlorines and Hydrogens, they would be pulling electrons with two different str...

Lisa Wang 3B

I agree with the previous answer and would just like to add that seeing a carboxyl group indicates that it's a weak acid, not a strong one, so that's definitely something to keep in mind. However, the COOH carboxyl group is stronger than a molecule with just an -OH group because the increased oxyge...

Lisa Wang 3B

As far as the textbook problems go, I think we just have to understand that K(a or eq) is calculated by [products]/[reactants]. Like the others have said, we will continue in 14B.

Lisa Wang 3B

There's the very basic memorization part of knowing if the salt is a strong/weak base or strong/weak acid https://www.google.com/url?sa=i&url=https%3A%2F%2Fopentextbc.ca%2Fchemistry%2Fchapter%2F14-3-relative-strengths-of-acids-and-bases%2F&psig=AOvVaw1h9X84Ic7qARY_SpX4315Y&ust=1607487733...

Lisa Wang 3B

And to add on, for part b all of the oxygen atoms have lone pairs but since the molecular shape is trigonal planar, not all 3 of the atoms would be able to bond to a metal atom at once. this is a good answer. Just to add on, you should also note that there is a resonance structure for Co3^-2 which ...

Lisa Wang 3B

I believe on the final we would be likely to calculate for the oxidation number given a chemical formula. For example [Ni(CN)4]^2- , in which case it will be helpful if you remembered that CN has a charge of -1. The answer to the example is that the oxidation number is +2. This was on one of the UA'...

Lisa Wang 3B

Correct me if I'm wrong, but I thought coordination compounds were a type of covalent bond. I think this has to do with the specific type of bond (such as single or multiple) that the compound has. We learned in Lecture 24 that whatever is [inside the bracket notation] means that it is inside the c...

Lisa Wang 3B

Like the above post has illustrated in the picture, I think you would look for atoms that have lone pairs. For example, nitrogen and oxygen predominantly.

Lisa Wang 3B

I usually go to my TA's office hours and ask them about reviewing my past midterms. I usually can learn a new technique or perspective when solving a problem during office hours.

Lisa Wang 3B

For some reason the answer booklet does not include 2.57 's answer. Does anyone have the answer to 2.57, specifically the 2 pi-bond hybridizations for Nitrogen? (C triple bonded to nitrogen, nitrogen has a lone pair).

Lisa Wang 3B

[quote="Using the same approach sp2 would have 1/3 or 33.3% s-character. A sp3 hybridized atom with 25% s-character has the bond angle of 109.5 degrees. A sp2 hybridized atom with 33.3% s-character (a great s-character) has the bond angle of 120 degrees (greater bond angle). " [/quote] i j...

Lisa Wang 3B

The final will be cumulative, so it will have everything we've learned. What I am curious is the percentage of material covered (will there be an emphasis on week 7+ OR an equal amount of everything).

Lisa Wang 3B

can someone please explain why minimizing the 90 degrees repulsions is ideal, so that lone pairs occupy the equatorial positions? Is it to keep the molecule as compacted as possible? To keep the molecule together?

Lisa Wang 3B

polarity is intricately tied with electronegativity and dipole moment is (in this example) tied with the positioning of the Cl. Think cis- and trans- molecules in this scenario. The largest dipole moment would come from the Cl atom whose dipole moments do not cancel, b and c both cancel because the ...

Lisa Wang 3B

I think in this case you would consider both Be and C in your thinking process. For example, actively noticing that Be is going to be in a linear structure with 2C's and that the 2C's are going to be in a tetrahedral structure with the H's. This way you can show your full understanding of the molecu...

Lisa Wang 3B

Please correct me if I am wrong, but I believe the size of the atom do not factor into the bond angle.

Lisa Wang 3B

I have a hard time memorizing and visualizing trigonal pyramidal, seesaw, and trigonal bipyramidal. Can someone show me how you memorized them/what seems to work? Thanks so much!

Lisa Wang 3B

Hi! since the carbon atom is the central atom and oxygen is double bonded to carbon, that leaves two fluorine atoms at a 120 degree position from each other. Like the above posts said, the electronegativities of both are very high but both are fluorine atoms so they are equally strong in electronega...

Lisa Wang 3B

(a) the thiosulfate ion, S2O32−; (b) (CH3)2Be; (c) BH2−; (d) SnCl2

for part b I like to think of it almost like 2 CH3's sandwiching the Be. So the central atom would be Be because of its low ionization energy. For part c Boron would be the central atom, and for part d Sn would be the central atom.

Lisa Wang 3B

Hi!
sp^3 would mean that s (1 orbital) and p^3 (3 orbitals) which corresponds to the 3 bonded pairs + 1 lone pair.

Lisa Wang 3B

the hypochlorite ion (ClO-) is covalently bonded, with the oxygen having a formal charge of -1.

Lisa Wang 3B

Since our last lecture that need be covered on the midterm was Wednesday, I don't think VESPER will be required on the midterm. I like to think that if you know it it kind of helps you understand the structure in your head better, so it doesn't hurt to learn about VESPER now.

Lisa Wang 3B

I attended a step up session and heard that there will be around 25 questions so the the general consensus is that there will be less point weight to each.

Lisa Wang 3B

they describe properties of the chemical. For example, the metals usually have low ionization energies. The post above mentioned metallic character, and that is quantifying how reactive a metal is.

Lisa Wang 3B

the structure that contributes the least to the overall structure is one that has the highest energy. Or the most unstable one. This can be the form of the least amount of covalent bonds, the most amount of formal charges, or one that does not apply the ideal "octet rule"

Lisa Wang 3B

hydrogen bond is using attractions of varying levels of electronegativity to make bonds, so it is different from a coordinate covalent bond.

Lisa Wang 3B

Jessica Katz 1G wrote: The radicals can damage DNA when they react with it and food supplements that we ingest can also react with radicals but that would be before any damage is caused.

Are you referring to oxidation when you say that "they react with it"?

Lisa Wang 3B

This hypothetical situation would not be a resonance because the electrons are still delocalized, like you said.

Lisa Wang 3B

Just to go over what the Kelter Method is... first you look at the name of the compound and find the number of electrons there should be. Then you multiply the number of electrons that would complete the octet rule (if we have CO3 -2) then it would be 4x8 =32 electrons. You then substract the initia...

Lisa Wang 3B

mlouie_1I wrote: If you are still unsure, you could compare the formal charge when the atoms are placed differently.

what do you mean by comparing the formal charge when the atoms are placed differently?

Lisa Wang 3B

Yes, the number of unpaired electrons is however many electrons that have only one electron in that orbital.

Lisa Wang 3B

The shape of the orbitals is the probable area that the electrons can be found in, and the equation that corresponds to this portrayal is the schrodinger equation and the schrodinger equation squared.

Lisa Wang 3B

Going off of what we know about salt, a salt consists of the positive ion (cation) of a base and the negative ion (anion) of an acid. Since we know that ammonium is a cation and sulfate is an anion, we know that ammonium sulfate is a salt.

Lisa Wang 3B

I asked my TA after the test on zoom, and she said it takes some time to sort the questions out since there are different versions and partial credit, like the above post said, so it will probably come out next week.

Lisa Wang 3B

electron affinity is the energy that gets released when an electron has been added to the atom, undergoing an exothermic process. Like the above posts had said, the affinity increases across the period and decreases down the group, similarly to the ionization energy.

Lisa Wang 3B

I usually like to do my puzzle and browse on amazon for fun!

Lisa Wang 3B

What you are saying is correct, as the n-level is increasing then the difference or "gap" should become smaller and smaller. Could it be that the variable shown in the image is wavelength and the other refers to the energy?

Lisa Wang 3B

So the n corresponds to the principal quantum number and the l corresponds to the angular momentum quantum number. In this case, I would just start looking at the leading coefficient for n. For l, I would recall the sequence of s, p, d, f and then s's l = 0, p's l = 1, and so on.

Lisa Wang 3B

Does anyone's textbook shows a part b of 2E.3? Mine just shows .
This is what I see:
2E.3 Draw the structures and name the shapes of the following molecules: (a) HCN; (b) .

Lisa Wang 3B

I think no one knows for sure if there's going to be more than one question on it until we take the exam. For me at least, it seems to be remembering the formula and then know when to use the components of the equation in the context of the word problem!

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