CHEMISTRY COMMUNITY

Hannah_Kim_1I

Oxidation: loss of electrons
Reduction: gaining electrons

In a galvanic cell, the reaction on the left is always an oxidation reaction and the reaction on the right is always a reduction reaction.

Hannah_Kim_1I

Dr. Lavelle, Thank you for the time and dedication that you put into your lectures. As a freshman, I was nervous because people always told me about how college professors don't care about their students. However, ever since the first day of Chem 14A, you have made it clear that you will be walking ...

Hannah_Kim_1I

Thank you for the reminder! I definitely would have forgotten.

Hannah_Kim_1I

If temperature increases, k also increases.

Hannah_Kim_1I

Since the slow step has an intermediate, you have to use the pre-equilibrium method. 1. rate = k 2 [HClO][I - ] 2. use the previous step (step 1) to find the equilibrium constant, K K = [HClO][OH - ] / [ClO - ] 3. rearrange equilibrium constant K in terms of the intermediate K[ClO - ] / [OH - ] = [H...

Hannah_Kim_1I

I always remember to remind myself that there's always a bigger picture and that one test won't ruin everything. Also, I like to go on bike rides to clear my mind and it has really been helping.

Hannah_Kim_1I

Lavelle said we should finish early so I'm assuming Wednesday would be our last? I think he did a review lecture for 14A so that might be on Friday. Also, we need to study all topics covered, but most of the problems will likely be from the larger topics covered in this class.

Hannah_Kim_1I

Since both your half reactions should be balanced, they should both show the same moles of electrons. That number of moles is what you use.

Hannah_Kim_1I

I would spend the most time with the harder topics/topics that were covered earlier in the class. Also, the biggest problem I ran into for the 14A problem was time management so try and be efficient when doing practice problems.

Hannah_Kim_1I

Could somebody explain why the solutions in galvanic cells need to be acidic or basic? Is it to create neutral solutions?

Hannah_Kim_1I

I believe they each correspond to different equations and cannot be used interchangeably.

Hannah_Kim_1I

Rocky by Still Woozy!

Hannah_Kim_1I

I took the 14A final and it was pretty unexpectedly difficult, but I'd say while taking the actual exam, time management was the most important. And to prepare, textbook problems and any old finals available.

Hannah_Kim_1I

One of my favorites is the Game of Thrones series!

Hannah_Kim_1I

Sadly, no extra credit. 50 points is the max.

Hannah_Kim_1I

Definitely not all will come from the textbook, but some will most likely be included.

Hannah_Kim_1I

Q: What did the scientist say when he found 2 isotopes of helium?
A: HeHe

Hannah_Kim_1I

Where do the two equations used to derive the Van't Hoff equation come from again?

Hannah_Kim_1I

Since calorimeters are isolated systems, you can assume there is no external temperature influence or change in amount of substance.

Hannah_Kim_1I

Since the equation for work of expansion in w=-PdeltaV, if the volume is constant, it makes delta v 0 since there is no change in volume. Since anything multiplied by 0 is 0, we can assume work will be 0.

Hannah_Kim_1I

I spent the weekend also eating to my heart's content and sleeping!

Hannah_Kim_1I

I believe ordered means how "scattered" the particles are. It's similar to how a room with a lot of clothing scattered everywhere has less order than a room with a pile of clothes in one place. You can use delta Svap to determine the most to least ordered by looking at which one has the la...

Hannah_Kim_1I

When we are adding equations (sapling #15) do the same rules that apply to delta H apply to delta S?

Hannah_Kim_1I

Criminal Minds!

Hannah_Kim_1I

Other than textbooks, I found it really helpful to write down steps for solving types of problems if Lavelle hadn't already done it for us in lecture. Also, every time I figured out how to do a problem I was struggling with, I made sure to write down what I learned so I can review before the midterm...

Hannah_Kim_1I

In #5 you need moles since you have to use C_V but they give you C_V,m so you have to multiply it by moles in order to get C_V. For knowing when to use it, I would just make sure that you're paying close attention to units given/asked for.

Hannah_Kim_1I

Don't trust atoms, they make up everything...

Hannah_Kim_1I

I was checking how many posts I have and there seem to be two different numbers. One says that I (before posting this) have 74 while the other says I have 80. Does anybody know why this is and which one I should be using?

Hannah_Kim_1I

I think Lavelle's example using gases helped me. The way I understood it was that in a system of gases, if entropy is at a maximum, it means that the gas has reached the most amount of disorder, meaning that it has spread out across the space of the system to the max. Since it has now occupied all s...

Hannah_Kim_1I

Calorimeters are used to measure how much heat is given off by a certain substance. It's related to thermodynamics because I believe it's another way to calculate enthalpy.

Hannah_Kim_1I

Hi! I can also totally relate. What helps me most is starting with something really small and easy. For me, that's usually like checking my email. That way I'm actually at my desk and it's much easier to start working that way. Then I start writing down a really specific set of goals I want to accom...

Hannah_Kim_1I

A neutron walks into a bar and asks the bartender how much a drink costs.

“For you, no charge.”

Hannah_Kim_1I

Thanks for taking the time to write these out! I'll definitely be implementing some of them into my studying before our next midterm.

Hannah_Kim_1I

Yes it can still transfer heat even if it is sealed. I don't know if the hot water would be exothermic, but it would be transferring heat to its surroundings if the surroundings were cooler.

Hannah_Kim_1I

If you're asking about why the slower work is more efficient than the faster work, it's because the slower one ends up getting more work done without using as much energy.

Hannah_Kim_1I

Enthalpy is denoted with H and refers to heat measurements whereas entropy is denoted by S and refers to the amount of disorder in a system.

Hannah_Kim_1I

I'd say a week give or take a day.

Hannah_Kim_1I

I believe it's because work depends on force and distance.

Hannah_Kim_1I

I (I₂) BRing (Br₂) Cookies (Cl₂) For (F₂) Our (O₂) New (N₂) Home (H₂) is the mnemonic I learned for the diatomic elements. But instead of saying cookies, I say Clookies since I could confuse it with carbon.

Hannah_Kim_1I

There's really no way of knowing for sure, but besides converting between partial pressures and concentration for gases, I could see Lavelle asking about how pressure and concentration are related (like how if pressure is increased, concentration would also increase).

Hannah_Kim_1I

Whenever something isn't a gas, you'll have to incorporate the enthalpy of the phase change. As for the corresponding values, I assume they will either be given to us or we will be able to figure it out.

Hannah_Kim_1I

What should you do if no one laughs at your chemistry joke?

Keep telling them until you get a reaction!

Hannah_Kim_1I

I'm still a bit confused about one of the textbook questions from outline 1 (5G.1). Could someone explain why "An equilibrium reaction is not affected by increasing the concentrations of products" is false? Is it because the equilibrium concentration of the reactants would then be larger?

Hannah_Kim_1I

For me, the textbook problems have always been a priority when studying. After I do those I usually look for any practice tests or worksheets from the TA/LA sessions.

Hannah_Kim_1I

If you meant that CH3COO and H30 had the same stoichiometric coefficients, then yes you are correct. We get the value by setting the Ka value equal to [CH3COO][H3O]/[CH3COOH] and plugging in the values from the ICE box to get 1.8 x 10^-5 = x²/0.1-x. Then solving for x you get 1.3 x 10^-3.

Hannah_Kim_1I

For chem 14A exam questions I remember having to be able to identify strong acids/bases so I definitely would memorize them.

Hannah_Kim_1I

State whether the following statements are true or false. If false, explain why. (a) A reaction stops when equilibrium is reached. (b) An equilibrium reaction is not affected by increasing the concentrations of products. (c) If one starts with a higher pressure of reactant, the equilibrium constant ...

Hannah_Kim_1I

I've always loved the Harry Potter series so the HP movies are always a good comfort movie for me (even though they definitely don't do the books justice...lol). I love watching them when I want to relax—especially after a tough school week!

Hannah_Kim_1I

This concept is pretty important since it applies to every acid-base reaction in this class since they're all aqueous solutions. Also, it isn't really like a constant in the way that we'll be using it specifically for certain problems, but I think it's more of a foundation for the other equations th...

Hannah_Kim_1I

Dr. Lavelle mentioned that increasing pressure by adding inert gases into a reaction would have no effect on the reaction. Is it because although the overall pressure of the container may change, the actual partial pressures of the reactants/products remain the same? I just wanted to make sure my re...

Hannah_Kim_1I

Yeah like other people said, as long as you have 50 by the end of the quarter, it should be fine. That's how it was last quarter.

Hannah_Kim_1I

Don't trust atoms, they make up everything...

Hannah_Kim_1I

Yeah I believe you have it correct. Another way to look at it is if Kc > 1, then the products are favored and if Kc < 1, the reactants are favored. Favored just means that at equilibrium, either more of the reactant or product are being formed.

Hannah_Kim_1I

A Lewis base is defined as an electron donor whereas a Lewis acid is an electron acceptor. Both of the oxygen atoms in the H2O2 molecule will donate one of their lone pairs by forming a coordinate covalent bond with the SO3 molecule, thus making the H2O2 molecule a Lewis base. The SO3 gains those e...

Hannah_Kim_1I

6.5 Hydrogen peroxide, H 2 O 2 , reacts with sulfur trioxide to form peroxomonosulfuric acid, H 2 SO 5 , in a Lewis acid-base reaction. My question is in regards to part (c) where we have to identify the Lewis acid and base for the reaction H 2 O 2 + SO 3 ---> H 2 SO 5 . The solutions guide says tha...

Hannah_Kim_1I

Does anyone have any tips on retaining the information we learned from 14A through to 14B? I know that I'll definitely be forgetting some things since we have winter break coming up.

Hannah_Kim_1I

Could someone go over the steps we should take when trying to identify a basic/acidic salt? Also, do we need to know what kind of salt forms when a weak acid and a weak base come together?

Hannah_Kim_1I

The substance you are looking at must be able to accept H+ (one indicator that it can accept another proton is a negative charge) and donate H+ as well, meaning that H+ would have to be somewhere in the formula. For example, looking at H 2 PO 4 - , it can both give away a H+ to become PO 4 2- , or ...

Hannah_Kim_1I

Something that might help is to think of Bronsted bases as "borrowing" protons from the Bronsted acid that is donating them.

Hannah_Kim_1I

A chelating ligand is a ligand that is able to bond to more than one site on the central metal by bending its bonds around to reach another bonding site. For it to be a chelating ligand, it needs to have a lone pair and flexible bonds (i.e. single bonds). I think the relevance is that if a ligand is...

Hannah_Kim_1I

Since the only allowed materials during exams are a periodic table, the formula sheet, and some scratch paper, I'd assume no.

Hannah_Kim_1I

Most likely a week after our finals since that's how long midterm scores usually took.

Hannah_Kim_1I

I'm planning on baking a lot more! Also the usual catching up on sleep and TV.

Hannah_Kim_1I

Since coordination numbers only apply to the elements inside the brackets, it might make it easier to find the number if you isolate what's inside the brackets.

Hannah_Kim_1I

Ariana Flores 3F wrote:Does anyone know if they count for credit?

I doubt they do. They're just meant to be tools for the professors and TAs for future quarters.

Hannah_Kim_1I

Happy (late) Thanksgiving! My family always likes to say one thing we're thankful for before we start eating.

Hannah_Kim_1I

Yes I believe you are correct.

Hannah_Kim_1I

Even if sigma bonds are able to move around, I don't think they would be able to make a polar molecule non-polar. The way I was thinking of it was that usually, polar molecules have lone pairs that are causing repulsion in the other bonds. So even if the sigma bonds moved, the lone pair would still ...

Hannah_Kim_1I

The 120 bond angle is the angle between the equatorial Cl atoms.

Hannah_Kim_1I

I believe that just means that when each of the s orbitals are bonded, they create a sort of cylindrical shape.

Hannah_Kim_1I

Yeah the final should be cumulative!

Hannah_Kim_1I

Since the phosphorus has 3 bonds and one lone pair, it would be sp³ cause there are 4 groups. This video might also help: https://youtu.be/4xl0BD-tMeA

Hannah_Kim_1I

We get Thursday and Friday off so I don't think we will be having discussions on those days, but Lavelle might still post a lecture for Friday since he posted a lecture when we had Veteran's day off. I would definitely be on the look out for emails though!

Hannah_Kim_1I

Technically, we get Thursday and Friday off for Thanksgiving break, but I remember Lavelle still posted a lecture when we had the day off for Veteran's day. I would assume that he'd still post a lecture on Friday.

Hannah_Kim_1I

Like most people have already suggested, re-doing textbook problems is most likely our best bet. I personally have a "cheat sheet" from both midterms that summarize the information that I personally struggled with that has helped me as well.

Hannah_Kim_1I

Kyla Villarama 3J wrote:Hi, I've also been struggling with remote learning. I came across this website that has background noises that I play when I'm studying and it's been really useful! mynoise.net

This website is super nice!! The rain/water sounds really help me focus. Thanks for the recommendation

Hannah_Kim_1I

You can definitely still assign a shape to a molecule even if the bond angles aren't all the same. For example, octahedral shapes have both 90 degree and 180 degree bond angles. I think the reason why Lavelle didn't assign the shape for NH3 was because he hasn't gone over shapes that include lone pa...

Hannah_Kim_1I

I believe it's because a bonding pair has a positive nucleus for each electron while a lone pair has 2 electrons for 1 positive nucleus, resulting in it having a larger density and thus more repulsion.

Hannah_Kim_1I

I think I saw something about the UA Justin holding another midterm review session tomorrow during his usual workshop hours.

Hannah_Kim_1I

Here's what Lavelle said in the "Test and Exam Schedule" pdf on his website: "All material is directly related to course content, readings, and homework problems. The best preparation for all exams is to be able to independently work through the assigned homework problems listed in th...

Hannah_Kim_1I

Lavelle has mentioned the importance of exercising our mind and body so I was interested to see what types of exercises everyone was up to! I usually just go for walks/runs with my dog.

Hannah_Kim_1I

Personally, I find it difficult to study at home. Before corona, I used to go to cafes or libraries, but due to obvious reasons I haven't been able to do that lately. Any tips on how to stay focused from home?

Hannah_Kim_1I

From my understanding, delocalized electrons are able to move around and occupy different orbitals since resonance applies to the whole molecule. This helps to complete the octet for orbitals making them more stable.

Hannah_Kim_1I

I checked the outline for the acid and base section but didn't find anything about Arrhenius acids and bases.

Hannah_Kim_1I

I find that in subjects like chemistry and math, the best way to get better/more consistent is to just practice a ton. Personally, I find myself getting things mixed up a lot so I always like to make sure I understand something fully and have a chance to practice it before moving on. Also, I think w...

Hannah_Kim_1I

I believe it's because the p-electrons experience shielding from the positive nucleus through the s-electrons.

Hannah_Kim_1I

Thanks for the helpful replies! Makes a lot more sense now.

Hannah_Kim_1I

To check my grades I go through the UCLA website under the class tab because I think it updates faster than the CCLE app. Under the class tab, where are you able to check grades through UCLA's website? Because I only see things such as "change grade type", "change units", etc......

Hannah_Kim_1I

Depending on how tired I am, I'll either nap, or just watch some of my favorite tv shows while snacking!

Hannah_Kim_1I

Hello! I was wondering if anyone else has yet to receive their textbook? I'm out of state so I assumed shipping would take a while, but I didn't think it would take this long. It's not a big deal since I have the online version, but I wanted to ask to see if I should email the publishers about it.

Hannah_Kim_1I

Hey guys! I know this is a silly question, but how do you make a post on Chemistry Community? I've only ever replied and haven't asked any questions on here and can't figure out how to do it. Thanks! Hey! To make a new post, you just need to login, scroll down to Chem 14A, pick the correct section ...

Hannah_Kim_1I

27. A bowling ball of mass 8.00 kg is rolled down a bowling alley lane at 5.00±5.0 m/s. What is the minimum uncertainty in its position? My method: \Delta p = (8.00)(10.0) \Delta x \geq \frac{(6.626 \cdot 10^{-34})(\Delta p)}{4\pi } \Delta x = 4.16 \cdot 10^{-32} The ...

Hannah_Kim_1I

My TA basically said the same thing. He said that it wasn't explicitly required, but that it would make our testing experience go a lot smoother if we did.

Hannah_Kim_1I

It should be 1s²2s²2p⁶3s²3p¹. I don't think we're expected to know how to do this yet since Lavelle hasn't gone over it in lecture.

Hannah_Kim_1I

Like everyone else has been saying, the textbook problems are probably the best study tool for us. I heard someone saying that since the textbook problems aren't required, Lavelle will most likely format his test questions similar to them to reward students who have been going through them. I think ...

Hannah_Kim_1I

So it seems like you did everything right until the last equation m(initial)v(initial)=m(final)v(final). What you want to do is plug in the molarity of the 150 mL solution, 0.210917673 mol/L, and the volume removed from that solution, 20 mL, into m(initial)v(initial) respectively. Since the question...

Hannah_Kim_1I

Yeah we definitely haven't gone over that equation in class so I wouldn't worry about it.

Hannah_Kim_1I

Personally, I've just been using the textbook problems as practice. As we get closer to the midterm, I'll probably go through my notes and try to summarize some of the main concepts making sure that I understand how they work and that I can explain them to myself. Also, I'm pretty sure my TA said th...

Hannah_Kim_1I

Since the Rydberg equation can be derived from E=-(hR)/n^2, you could use them interchangeably. However, Lavelle seemed to favor E=-(hR)/n^2 since it is more informative and requires a deeper understanding of chemical principles rather than just plugging in numbers.

Hannah_Kim_1I

I know Lavelle mentioned that Black Body radiation isn't really a chem 14A topic in one of his lectures. I doubt that he'd test us on laws related to it.

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