CHEMISTRY COMMUNITY

LeanneBagood_2F

is there a reason WHY platinum is like the default thing we use?
are there any situations where we would add a different element (?) as an electrode? if so, what are those elements and how we would tell which one to use?

LeanneBagood_2F

wait, can someone remind me the difference between a concentration cell and a galvanic cell please?

LeanneBagood_2F

in terms of equations/laws, which ones can/cannot have catalysts and/or intermediates in them again?
i saw someone mention that intermediates can't be in rate laws but is there anything else?

LeanneBagood_2F

I've heard about an open, closed, and isolated system but what exactly is a perfect system?
What characterizes such a system and are there any examples besides a bomb calorimeter?

LeanneBagood_2F

i understand why adding a catalyst will decrease the activation energy for the forward reaction, but im a bit confused as to why it's the same for the reverse. can someone explain this please?

LeanneBagood_2F

can someone please remind me what exactly molecularity is used for again? i understand how to find it (i think) but im still a bit confused on what to do after that.

LeanneBagood_2F

can someone sort of summarize what characteristics of the line give away what order it is? or maybe link a different question thread that answers this please?

LeanneBagood_2F

can someone please clarify what a biomolecular equation is please? like what are some things you can look at to know if an equation is biomolecular and why it's significant to note this?

LeanneBagood_2F

i've seen this mentioned a few times in this thread but what are we referring to when we mentioned potential outcome? and can someone explain a bit more in depth as to how that is controlled by rate of formation?

LeanneBagood_2F

Outside of Sapling and more generally, can someone please explain how to determine states of matter when balancing redox reactions?
I finished the Sapling homework and all but I did not completely understand it.

LeanneBagood_2F

just to add on, others have mentioned that solids need to be on the outermost part on both ends. something i learned recently from my AAP PLF is that, if there is not a solid on either/both sides, then you would need to add platinum - "Pt(s)" - wherever needed. i forgot the exact reason fo...

LeanneBagood_2F

like other's have said, a coulomb is essentially another unit for charges.
if you take physics (at least this is the case for physics 5C) you'll be seeing it used a lot more

LeanneBagood_2F

while i get that we can sorta just memorize that positive = reduction and negative = oxidation, why exactly is that?
like what sort of concepts explain why that is?

LeanneBagood_2F

just for some clarification, when we say "strength" in relation to reducing/oxidizing power what exactly do we mean?

LeanneBagood_2F

i always get a bit confused with this but can someone briefly explain what exactly dilution is please?
i guess more specifically, what it means to dilute something/what is happening when something is being diluted

LeanneBagood_2F

i think the easiest way to know which value of R to use is to look at the units of the other values you are given in the question. based on that, you can determine which R value to use as your objective is to cancel things out so you are left with the correct units for your answer.

LeanneBagood_2F

this sounds very unfamiliar to me, was it mentioned in lecture previously? if so, can someone tell me which one please?

LeanneBagood_2F

wait im a bit confused by this. what exactly are we referring to when we're talking about stable vs unstable? like of the compound?

LeanneBagood_2F

can someone remind me what residual entropy is please?

LeanneBagood_2F

is 'W' in any specific units?

LeanneBagood_2F

yes! My AAP PLF mentioned recently that not converting the temperature to Kelvin is a common mistake amongst students. it's best to get into the habit of always converting temperature to Kelvin, even if sometimes you can get away with leaving it in celsius (ex: when equations use delta/the change in...

LeanneBagood_2F

wait, can someone please explain what exactly is meant when we say "as written"? has that phrasing ever been mentioned in lecture, if so when/which one?

LeanneBagood_2F

can someone explain a bit more about how things will look differently in the equation/value if we are talking/using delta g naught vs delta g please? im a bit confused still

LeanneBagood_2F

wait what exactly are bomb calorimeters? has this mentioned in lecture before? if so, when/where and how solid should we be on this topic?

LeanneBagood_2F

like others have already said, which equation you use depends on what you are being given in the question. if something is given in terms of mass (grams usually), then you would use q=mCAT whereas being given moles would mean you use q=nCAT

LeanneBagood_2F

going off of this, on exams will we only be given situations where we are only dealing with isothermal reversible expansions so that we can use those equations or is there a chance we'll be exposed to other instances where we'd have to use other ones? if so, what would those equations be?

LeanneBagood_2F

Going along with this, can someone please explain a bit more conceptually what the difference is between a reversible and irreversible expansion?

LeanneBagood_2F

Adding on to this question, i keep getting extensive/intensive properties confused with state/non-state properties (?).
Can someone please, i guess, connect these two and explain how they relate to one another and/or how to distinguish between them?

LeanneBagood_2F

i was reading through this thread and i saw the word "diatomic" come up a bit - can someone briefly explain what this means again please?

LeanneBagood_2F

I am still confused with the bond enthalpy method...

how exactly do we determine/know which bonds are being formed and which are being broken? would we have to draw a lewis structure or are there ways for us to just know?

LeanneBagood_2F

this is a bit late but grades, at least based on my experience in 14A in the fall, will be released within a week to a week-and-a-half from when the last group of students have taken the exam. this is because the Dr. Lavelle and the TAs will review the questions/exams and reassign points (ie partial...

LeanneBagood_2F

sort of going off the original question, can someone briefly explain what deprotonation is again please?

LeanneBagood_2F

hello!! so i understand that the internal energy and pressure is constant in an isolated system, but im a bit confused about the second part of the original question. was "constant external pressures" a mis-type or is it possible to apply that to an isolated system? if so, how?

LeanneBagood_2F

as everyone has already said, temperature is always in Kelvin. this is not limited to just the PV = nRT equation as we will see throughout the remaining weeks

LeanneBagood_2F

hello!! i had a question about the last example Dr. Lavelle went over in today's lecture (around the 50:30 min mark).

Why is the temperature used in the equation +6.9 degrees Celsius? And if it was through some sort of calculation, what was that process?

LeanneBagood_2F

Just to make sure I understand, the value of R is the same - the only difference is the units. And then the way to determine which units we use depends on what we are trying to find? Like, we would look at which units would cancel out and help us find the answer?

LeanneBagood_2F

to add on to this question, can someone sort of explain more what a catalyst is and give examples?

LeanneBagood_2F

As everyone has already said, going over the textbook problems help but also make sure that you understand the concepts behind equations/principle's as not all the questions on midterms involve actual calculating.

LeanneBagood_2F

As others have already stated Q and K are not the same.
While they do use the same equation, they are used for different situations. K is specifically at equilibrium whereas Q is for at any point during the reaction.

LeanneBagood_2F

As everyone has previously stated we are allowed to use a calculator during the exam as well as two sheets of paper - Equation Sheet and the Periodic Table. Regarding scratch paper, my TA last quarter in 14A did NOT allow us to use any beyond the two sheets of paper. Additionally, it is important th...

LeanneBagood_2F

hello! others have already answered your question but i would like to also put in my own two-cents. during my AAP PLF session this topic came up and the way i sort of learned to think about it is: what is Q doing to try to reach equilibrium (K)? in the case Q<K, Q will (over time) increase. this mea...

LeanneBagood_2F

this is my opinion, but for this class i think we should have a pretty solid understanding of what is meant by a conjugate seesaw for possible conceptual questions on the exams. additionally, it may help to have a good grasp on this topic as it could be applied to non-conceptual questions as well (e...

LeanneBagood_2F

since there's sort of two values being given, just to check my understanding, K should be less than 10^-3 but to be safe (as values can be close to one another) we should just use 10^-4 as our sort of baseline to determine when x is negligible?

LeanneBagood_2F

so i understand that if the equilibrium constant is less than 10^-4, approximation is okay.
i am a bit confused/curious though as to why 10^-4 is the baseline or value that allows for approximation. is that just something memorize or is there reasoning behind it?

LeanneBagood_2F

Adding on to this, does anyone know/has anyone heard how the Zoom calls will work this quarter since we aren't taking the exams during our discussion?

LeanneBagood_2F

You should be careful with the liquids. While solvents aren't taken into account for the K value, liquids that are reacted together can be involved in the K concentration. can you (or anyone else who reads this) please explain this a bit more? i thought for the sake of this class we only take into ...

LeanneBagood_2F

This is also a sapling related question but I'm having trouble figuring out where to go for the Chem14B homework... I took 14A last quarter so all I see is my work from Chem14A. Does anyone know how to access the Chem14B homework? this may have already been answered but i access my 14B homework by ...

LeanneBagood_2F

for this course do we prefer one unit over the other? or does it really just depend on what the question is asking for?

LeanneBagood_2F

what exactly does R represent?
im a bit confused since it can be equal to different values depending on the units

LeanneBagood_2F

like others have previously said, the way you can tell if you use Kc or Kp is by looking at the units you are given in the equation. Kc is when you use mols whereas Kp is when you see atms/bars

LeanneBagood_2F

like others already said, yup! one is in term of electrons while the other is in terms of hydrogen ions

LeanneBagood_2F

im sorry im blanking, can someone quickly explain what an amphoteric compound is please?

LeanneBagood_2F

as others have already mentioned, yes, you should have at least a general idea of the bond angles of each structure. this includes knowing the values (90, 109.5, 120, 180) and whether the angle is the value itself or if it would be less than that value (<90, <109.5, <120, <180).

LeanneBagood_2F

like others have already mentioned a grading scale hasn't really been set for this class beyond a C- = 50%. i would like to assume that Dr. Lavelle is waiting until after the final to curve the rest of the grades based on what our class distribution is. something to remember with this is that grades...

LeanneBagood_2F

Hello!
so i did some digging through old posts and found this thread that was created prior to midterm 2:
viewtopic.php?f=157&t=67682&hilit=update+respondus

hopefully that link works and that it helps you!

LeanneBagood_2F

adding on to this question, how do we know the charge of a ligand (ie if it is neutral or not)? is that something we just need to memorize or is there a process to figure it out?

LeanneBagood_2F

What about when you're presented with the names+prefixes already and you have to find the opposite?
Like, does the order you write the ligands/formulas in the square brackets matter?

LeanneBagood_2F

Would it be better for us to just memorize which are the most common polydentate ligands or should we get into the habit of drawing the lewis structure?

LeanneBagood_2F

Someone please correct me if I am wrong, but I do not believe we will be given any opportunities for partial credit on the final as the exam is multiple choice. Unless the final exam changes to free response, there likely will not be any chance for partial credit.

LeanneBagood_2F

this was asked earlier but curving grades should NEVER hurt or bring down a student's grade, it should only help it if ever. this applies not only to this course - if Dr. Lavelle does curve our grades - but any class that says they will do so at the end of a quarter.

LeanneBagood_2F

just to clarify, the best way to determine if there is a delocalized pi bond is to first draw a lewis structure and then see if there is resonance? if there is resonance then there is a delocalized pi bond, but if not, there is none? can someone briefly explain how resonance connected to a delocaliz...

LeanneBagood_2F

so the only thing needed for a chelate is that there needs to be multiple lone pairs? and once something is a chelate we automatically know it'll form a coordinate compound?

LeanneBagood_2F

To add on to this, are there any Lewis structures that you all think we should all be pretty solid with? Like not necessarily know them by heart but be able to do them with ease if that makes sense?

LeanneBagood_2F

I have spoken a bit with some upperclassmen who have previously taken Chem14A with Dr. Lavelle and/or have been an AAP PLF for him and they have stated that he typically curves grades at the end of the quarter, hence why he may not have provided an exact grading scale on the syllabus. Not 100% if th...

LeanneBagood_2F

Like some have already stated, our Chem 14A final is set for Sunday, December 13. I believe on MyUCLA it mentions the time, which is 11:30AM - 1PM PST. I would like to assume this is correct as the syllabus states that we will have a final that lasts for 1 hour and 30 minutes. Additionally, the syll...

LeanneBagood_2F

this is a bit of a dumb question but what exactly do we mean when we say something is delocalized? i've seen it in a couple of posts and im a bit confused as to what that exactly means

LeanneBagood_2F

As a sort of follow up question, if an atom has a triple bond is it locked into position or is it able to move around?

LeanneBagood_2F

Hello! As everyone else has already mentioned, memorizing a VSEPR chart would probably be the best thing to do. If it is of any help, my PLF said that the most common ones we will see are structures with 0, 1, and 2 lone pairs so it would be best to be solid on those. Structures with 3+ lone pairs c...

LeanneBagood_2F

I am not the best with memorization so I was a little bit worried about getting down all the different molecular shapes and their corresponding VSEPR formula. Does anyone have any tips on the best ways to help yourself remember? Thank you! Hello! I mentioned this on a different post but my PLF rece...

LeanneBagood_2F

Hello! My PLF for this course recently suggested we use the charts online to create flashcards to help memorize the different molecular shapes. Their suggestion was to have the steric number, number of lone pairs, and the VSEPR formula on the front while the name of the shape, bond angle, and hybrid...

LeanneBagood_2F

adding on to this, where would van der waals be in the order?

LeanneBagood_2F

Adding on/to reiterate what has already been said, there are two things needed to create a hydrogen bond: 1) a Hydrogen acceptor (this can be F, O, N, or S) 2) a Hydrogen donor (hydrogen; only if it has a partial positive) sort of disclaimer: this is information that I received during an AAP PLF ses...

LeanneBagood_2F

Does anyone know if Dr. Lavelle will be using bent and angular interchangeably or if only one will be used on the midterm/final exam? I understand that they're the same thing, but I would like to know which one we should get more used to using if possible.

LeanneBagood_2F

though the explanations make some sense, im still a bit confused in the process of finding the actual value of a bonding angle. can someone possibly explain an example? maybe one of the ones from lecture?

LeanneBagood_2F

In today's lecture Dr. Lavelle said that the repulsion strength of electron regions is lone-lone pair>lone bonding pair>bonding-bonding pair. What is the difference between a lone-lone pair and a lone-bonding pair or a lone bonding pair and a bonding bonding pair? Thank you! Adding on to this quest...

LeanneBagood_2F

Adding on to what's already been said, if we are expected to use the formula to actually calculate or solve something it would likely be provided on the equation sheet we're allowed to have during tests. I'm not sure if Coulomb's potential energy equation is there, but I would recommend checking!

LeanneBagood_2F

To add on to this question, what are some more theoretical approaches to determining whether a bond is ionic or covalent? Audra gave the example of observing its solubility in water, but if we were in a situation where we are unable to do that how else could we determine the type of bond? I know we ...

LeanneBagood_2F

To add on to this question, will bond lengths always be given to us in a problem or will we sometimes have to calculate it? If so, what would the process to do that look like?

LeanneBagood_2F

Adding on to this, I am not sure if anyone else has taken Physics 5B but is the concept of electron diffraction in chemistry similar to what we learn about in 5B with light diffraction?

LeanneBagood_2F

Looking at the row in the periodic table always helps me. When you count the rows [1,2,13,14,15,16,17,18] when you omit the d block. You can see that the number of electrons correspond to the row because there are 8 rows. Hope that makes sense! Quick question, can you explain why you omit the d-blo...

LeanneBagood_2F

Adding on to this, does anyone know to what extent we will need to know this for the second midterm?
We haven't talked about acids/bases but I do know that it is mentioned in the syllabus, not sure if we'll cover it by week 7 though.

LeanneBagood_2F

To add on to this question, we would determine which element has the lower ionization energy by the trends in the periodic table right? And that's something you just sort of have to memorize?

LeanneBagood_2F

As many of our peers have said, no, we will not need to know f-orbitals as in depth as the s, p, and d-orbitals.
I am in AAP and my PLF said that it's good to know that they are a thing and exist, but that's pretty much as far as this class will go with f-orbitals.

LeanneBagood_2F

I thought it was 50 posts at the end of the quarter! Do we have ways to make up? This is what I thought so too because, according to an upperclassman that took Chem 14A with Lavelle in the past, as long as you have the required number of posts by the end of the quarter we should get full credit. I ...

LeanneBagood_2F

Has Dr. Lavelle said whether we will be able to write on these printouts once the exam begins? Or should we have separate papers for scratch work?

Additionally, do we know if these will be the same printouts for our second midterm and final?

LeanneBagood_2F

Also just to confirm, Respondus will log us out of the test once 50 minutes has passed right? Even if have not necessarily finished?
Does that mean our "additional 5 minutes" are for BEFORE we begin the exam?

LeanneBagood_2F

I believe that he was demonstrating that the upper bound of l is n-1. It can take on any possible values from 0 to n-1, with n-1 being the upper bound value. I don't think that if n=2 l could equal 1, but it could equal 0 or 1. This is a chart that I used to better understand it. When n=3, l can ha...

LeanneBagood_2F

Adding on to this, to clarify, the electrostatic potential equation is different than Coulomb's Law right? Because in Coulomb's Law there is the constant k in the equation as well?

LeanneBagood_2F

Minahil_Tufail_1L wrote:Hi, I'm confused on how to figure out when electrons are either paired or have parallel spins. Is there a general rule to determine this?

To add on to this question, can someone please clarify what it means for a spin to be "paired" or "parallel"?

LeanneBagood_2F

this might be a dumb question but i'm blanking: how do we determine electronegativity? is there something we'd look at on the periodic table or something like that?

LeanneBagood_2F

in the Rydberg equation is the n^2 in the denominator always the initial energy level? As Will said in their post, the "n^2" in the denominator does NOT refer to the initial energy level. "n", unless otherwise specified, is just an energy level. In the case of the example proble...

LeanneBagood_2F

For the equation V = -R((1/n^2)-(1/n^2)) How do we know which n value (the final or initial n value) to put first in the equation? Some of our classmates already responded with this but the difference of something is always going to be found by calculating final - initial . Because of this, the fir...

LeanneBagood_2F

is the Rydberg equation just E= -(hR)/(n^2) ? I believe that the equation you mentioned is the empirical equation for an H-Atom. Rydberg's equation is similar but still different. Here is the equation based on a quick Google search. Pretty sure this is correct though because I vaguely remember usin...

LeanneBagood_2F

Ex. Calculate the frequency of light emitted by a hydrogen atom when an electron makes a transition from the fourth to the second principal quantum model. I understand how professor lavelle changed the equation from e=hv to v=e/h to find the frequency. But i do not understand where the fractions su...

LeanneBagood_2F

Adding on to this question, is there a specific way we should be writing the "v" or frequency in the equation E = hv? Every lecture I get a bit confused because the symbol for frequency looks exactly like "v" for velocity and i'm not too sure how to make a distinction.

LeanneBagood_2F

So is the consensus that if we are able to use a second device (ie a phone or another laptop) to show our workspace for the duration of a test/exam we do NOT need to buy a webcam?

LeanneBagood_2F

I know the rules of sig figs, but when we have problems that requires multiple steps/calculations, should we follow the rules of sig figs for each step, or should we have numbers with more sig figs than what is technically allowed and just make sure the final answer has the correct number of sig fi...

LeanneBagood_2F

sorry if this is a sort of dumb question but what is an angstrom? is it something we will need for this course?

LeanneBagood_2F

For the Audio-Visual Topic: Photoelectric Effect the professor states in the module video that the Photoelectric Experiment is done under a vaccum. What does this mean? Hello! This may be repetitive but something in "vacuum" essentially means a space devoid of any matter/particles. I thin...

LeanneBagood_2F

Will we be penalized for not including the state of each element in the chemical reactions? It's easier for me to visualize the formula without the extra information but I don't know if that's something that's important to have in the answer. To add on to this question, does anyone have any tips fo...

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