CHEMISTRY COMMUNITY

Bailey Giovanoli 1L

Are we allowed to highlight equations on the constants and equations sheet?

Bailey Giovanoli 1L

Does anyone know if any equations or constants have been added to the equation sheet since midterm 2?

Bailey Giovanoli 1L

I agree! It’s the number of moles of electrons transferred, make sure to check that you have multiplied the half reactions by a constant so the two reactions put out the same amount of electrons if they do not naturally.

Bailey Giovanoli 1L

Do I need to use the Nernst equation because of the pH?

Bailey Giovanoli 1L

I'm a little confused with question 6O.3 from the assigned book problems. The part that I'm slightly confused on is the Standard Potential of H2O. The answer key states it to be -0.42 at pH 7, but Appendix 2B (where you find the standard cell potentials) states it to be -0.83 under standard conditio...

Bailey Giovanoli 1L

In one of the sapling problems for week 7 and 8, we had to use the Nernst equation. However, we were given partial pressure for the products and molarity/concentration for the reactant. You got the problem correct if you left the units as is and plugged the numbers in. Why is it that you can use par...

Bailey Giovanoli 1L

Wait... is it based off the number of moles of electrons being transferred?

Bailey Giovanoli 1L

I know in class, Lavelle said something about n in debt G= -nFEcell and how he always gets questions about how to determine it. I am now going to be one of those people. I don't quite understand how we know which value to use for n when there are differing moles of reactants in the redox reaction. S...

Bailey Giovanoli 1L

The breaking up the OH- and H+ can make it way clearer!

Bailey Giovanoli 1L

Here's the steps I use: 1. Balance elements other than O and H 2. Balance O using H2O 3. Balance the Hydrogens using H+ 4. Check the overall charges on both sides and add electrons to the side with the greater positive charge to balance the overall charges 5. Combine the reactions by multiplying th...

Bailey Giovanoli 1L

Here's the steps I use: 1. Balance elements other than O and H 2. Balance O using H2O 3. Balance the Hydrogens using H+ 4. Check the overall charges on both sides and add electrons to the side with the greater positive charge to balance the overall charges 5. Combine the reactions by multiplying th...

Bailey Giovanoli 1L

For some reason, I cannot balance this half reaction:
N2H4-->NO (in basic conditions)
I have a pretty good understanding of half reactions, and can do any other half reaction balancing. However, I cannot seem to get this one. Does anyone have any tips?

Bailey Giovanoli 1L

Just to clarify, because the voltage will always be positive, the standard reduction potential, E naught, will always be positive, right?

Bailey Giovanoli 1L

To add on, you know that all energy that leaves the benzene will enter the calorimeter because it's isolated. Therefore, you know the heat absorbed by the calorimeter is equal and opposite of the benzene reaction because none goes outside the calorimeter.

Bailey Giovanoli 1L

I'd agree with going over the textbook problems. Although every topic we cover will be on the exam, I would recommend paying the most attention to the topics we spent the most time on when you study. These topics will likely pop up the most on the final.

Bailey Giovanoli 1L

Final is cumulative, anything we've learned is fair game. However, the topics we spent more time on will be a larger portion of the final.

Bailey Giovanoli 1L

Last time, I feel like it took a little longer than in 14A. I would expect next weekend/Monday at the earliest!

Bailey Giovanoli 1L

Are all reversible expansions isothermal? If not are all the ones we look at isothermal? If not, is the formula for the two the same? If they’re different how so? What are the two different equations in that case?

Bailey Giovanoli 1L

So qrev just shows that it was a reversible expansion! I'd assume normal q is just an irreversible one because it was not specified as reversible.

Bailey Giovanoli 1L

If the Q and the K relationship is all that you're struggling with, I'd make sure to remember that the reaction process moves from left to right. Q=K in the middle, and the the right of the middle, Q>K because there are more products because products appear on the right side of the equation. An to t...

Bailey Giovanoli 1L

I was looking over the information sheet Lavelle sent out for Midterm 2. On the Midterm 1 sheet, it stated a rough estimate of the number of questions that would be on the exam. I didn't see this on the Midterm 2 sheet. I just want to make sure, I'm not just looking over it.There's no rough estimate...

Bailey Giovanoli 1L

So, I was thinking, is this because at constant pressure, delta H =q?

Bailey Giovanoli 1L

You are asked to calculated the final temperature and change in enthalpy for the system when 765J pf energy is transferred to a system with 0.820 mol, T=298K, and 1 atm at (a) constant pressure and at (b) constant volume. I calculated the final temperatures to be (a) 343 K and (b) 373K. My question ...

Bailey Giovanoli 1L

I think everyone's problems vary slightly in numerical values. However, if you are looking to find work, you may need to use P(delta V)=(delta n)RT to find your volume change or pressure.

Bailey Giovanoli 1L

Update: I was overthinking it lol.

Bailey Giovanoli 1L

Would I need to convert using the density factor, or am I overthinking it?

Bailey Giovanoli 1L

Okay, thank you everyone. One more question though. How do you calculate the specific heat of the calorimeter using L when you need mol or grams for the q equation?

Bailey Giovanoli 1L

Im having trouble figuring out conceptually what I need to do in number 19. I know how to calculate delta U and the specific heat capacity. I just don't understand where the neutralization reaction comes into play in the question: A constant‑volume calorimeter was calibrated by carrying out a reacti...

Bailey Giovanoli 1L

For anyone who was thinking of tackling this, I figured it out. Apparently I think water is h2o2:( when calculating the moles of water. So, thats how my days going.

Bailey Giovanoli 1L

An ice cube with a mass of 53.8 g at 0.0 ∘C is added to a glass containing 384 g of water at 45.0 ∘C. Determine the final temperature of the system at equilibrium. The specific heat capacity of water, Cs, is 4.184 J/g⋅∘C, and the standard enthalpy of fusion, delta H∘fus, of water is 6.01×103 J/mol. ...

Bailey Giovanoli 1L

Okay, I just wanted to make sure he hasn't responded and said something to someone on chem community.

Bailey Giovanoli 1L

I know last quarter it took Lavelle at least a few days to get an email out about the midterms and finals. Does anyone know if he's said anything on when he thinks results might be available?

Bailey Giovanoli 1L

I know we started on open and closed systems on Friday. Dr. Lavelle referred to this section as thermochemistry, does this mean we're finished with thermodynamics? I ask because I don't think we covered all the topics in the thermochemistry outline. Does this mean we're still doing the thermochemist...

Bailey Giovanoli 1L

Can someone describe to me why a larger equilibrium constant is associated with higher solubility?

Bailey Giovanoli 1L

what would be the best way to study for that topic? I’d suggest just knowing which cations acid as acids. You won’t need to remember there Ka values. Those should be given in any question, and if they aren’t you’ll be able to solve for them. As a rule of thumb for cations that act as acids, you can...

Bailey Giovanoli 1L

Does anyone know if Lavelle is planning on having a lecture the day of the midterm?

Bailey Giovanoli 1L

Okay, so Al3+ is the acidic component that gives of the proton. In this case, I don't believe you transfer an atom as you would if there was an H. Instead, the charge of the AlCl3 would just become negatively charged. As for the table, when I did this problem, I couldn't find the table that listed A...

Bailey Giovanoli 1L

I do believe you're right. I think you monitor the temperature, and whatever temperature is reached that is the highest/lowest during the rxn is the number you would use to gauge your overall temperature change in relation to the initial temperature.

Bailey Giovanoli 1L

In Friday's lecture, Lavelle talked about diatomic molecules. I know any molecule that is made up of two of itself is diatomic (Ex:O2), but he also listed HCl as diatomic. My question is, how do we know a molecule is diatomic if it is not two atoms of the same element?

Bailey Giovanoli 1L

I agree with the following the outlines from each unit. In terms of making a study guide, I would recommend making your own out of the outlines and putting book problems as examples if that makes sense. Also, considering the midterm is multiple choice and will likely be a fair amount of math, I reco...

Bailey Giovanoli 1L

I don’t know how everyone else navigated the book problems for this week, in terms of which ones we should do because we’re going a little out of order. Me and my friend looked at the book problems and the reading Lavelle said would be the focus this week and we think theses are the problems we thin...

Bailey Giovanoli 1L

Just to clarify, you can ignore the second or even third deprotonation in polyprotic acids when the first Ka is greater than the Ka in the second and third proton transfer.

Bailey Giovanoli 1L

What I took from the lectures is that the solvent will be on both the reactant and product side. Therefore, when you put it in the equilibrium constant, it will cancel because it would be present on both top and bottom. I also believe it will clarify that a reactant is a solvent if it is not H2O.

Bailey Giovanoli 1L

When you do the ICE box, the stoichiometric ratios are what determine this. If you have x of both CH3COO- and H3O+, then they will both have the same concentration.

Bailey Giovanoli 1L

Keerthana Sundar 1K wrote:I see those in table 6D. 1, so in the first table of the Solutions of Weak Acids section (6D). Does that help?

Yes, I think I figured it out. Thank you!!

Bailey Giovanoli 1L

In section 6E.1 of the textbook, it states that you only take the first deprotonation into account when calculating pH. It hints that there are exceptions like sulfuric acid. What are the other exceptions? How do you identify them?

Bailey Giovanoli 1L

Does anyone know if the book shows the equilibrium constants of cations that are acids, like Al3+? I thought I saw it somewhere, but I can’t find it now.

Bailey Giovanoli 1L

A change in concentration does not change K. Concentration change does not affect K because the ratio of reactants and products formed from the increase will offset the increased concentration of one of the reactants or products. For example, if you added more product, the reaction would be out of e...

Bailey Giovanoli 1L

On 5.35 it asks you to write the equation of A decomposing into B and C, given a graph(which I couldn’t figure out how to insert). Essentially it shows A coming from a partial pressure of 28 to 18 so the difference is 10 (I use this as my stochiometric coefficient), and B going from 0 to 5, and C fr...

Bailey Giovanoli 1L

So, the equation for Equilibrium constant, K, is the same as that of the reaction quotient, Q. However, I’m assuming you’re asking how to do it because there are no values given. In this case you would just express the equation symbolically. For example if your equation were 2O3-><-3O2, then you wou...

Bailey Giovanoli 1L

In question 5 of section 5J it asks you to identify whether products or reactants are favored if total pressure is increased. From what I gathered with Le Chatelier’s principle, if total pressure is increased, the side of the reaction with less moles will be favored. I think this is because if there...

Bailey Giovanoli 1L

I've been noticing that in some of the sections, such as 5I.2, there are yellow boxes titled "How it is explained." I noticed these boxes contain one section on thermodynamics and tend to be heavily based around Gibbs Free Energy. In Lavelle's discussion earlier tonight, he said we would t...

Bailey Giovanoli 1L

When talking about London Dispersion force strength, in what trend does it increase? Does anyone know if there is a trend?

Bailey Giovanoli 1L

I asked my TA and she said that we would not need to know how acids or named because that will not be covered on the exam. I asked her because one of the homework problems said to name the acid. She reassured me that because Lavelle never went over it in class you will not be expected to name them, ...

Bailey Giovanoli 1L

Can anyone explain to me what amphiprotic is? How do I identify it?

Bailey Giovanoli 1L

What I got from the lecture that included polyprotic acids and bases, essentially anything that has the potential to give or accept more than one H+. Obviously, there are likely more parameters to be met for this to actually be true, but this is the fundamental idea, correct?

Bailey Giovanoli 1L

Okay, this makes much better sense now. Thank you:)

Bailey Giovanoli 1L

I've always struggled a little with molarity calculations, so this question confuses me a little: A careless laboratory technician wants to prepare 200.0 mL of a 0.025 M HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have bee...

Bailey Giovanoli 1L

It's simply the number of bonds. Unless you're dealing with a polydentate ion, then I believe you may have to take that into account. For example, if you have a bidentate ligand bonded to a metal I believe the coordination number would be two and not one. I hope this helps:)

Bailey Giovanoli 1L

Ohhh I think I understand what you're saying, but let me clarify. It could be monodentate because the shape allows for another molecule to come and bond to both regions simultaneously. This is because the Oxygens are close enough together in terms of shape, right? In that case, it would also be a ch...

Bailey Giovanoli 1L

On 6A.7 in the textbook, you are asked to name the molecules in the image and find their conjugate base. I understand how to find the conjugate base, however, I am struggling with naming acids like H2NO. Does anyone have any tips on naming acids?

Bailey Giovanoli 1L

The book asks whether the ligand is polydentate and if so to determine the maximum number of places the ligand can bind simultaneously. You are given CO3 with a -2 charge. When I draw the structure I see that one of the oxygen has a double bond. Therefore, it will not want to bind because it is stab...

Bailey Giovanoli 1L

I'm sure there is more technicality to it, but typically strong bases are alkali metal oxides and hydroxides (group 1), as well as alkaline earth metal oxides and hydroxides (group 2).

Bailey Giovanoli 1L

When an acid is referred to as weak, it means the bond is harder to break, right? Please correct me if I am wrong!

Bailey Giovanoli 1L

You can find the hybridization orbital by counting the number of electron density regions. From there, you know that s can hold one pair, p can hold 3, and so forth. For example, if phosphorous has 3 regions of electron density, then the hybridization orbital is sp2. This is also the idea that the n...

Bailey Giovanoli 1L

I'm not so sure that he was looking at the electron configuration. I think he was using his knowledge on VSEPR shapes, and how they couldn't be in the same plane because whenever he talks about 90-degree bonding angles not being desired he seems to be talking about VSEPR and how it allows for the us...

Bailey Giovanoli 1L

We hybridize because the energy gap between the s and p orbitals is large. If we hybridize, we create an orbital in between the two. It is then less energy to jump to the p orbital than pair in the sp. This is because when you pair electrons, there is electron repulsion.

Bailey Giovanoli 1L

So, essentially a polar bond is a bond where the electrons are not shared equally. You can tell this by looking at the electronegativity of the individual atoms. The higher the electronegativity difference between the two atoms the more polar the bond is. In terms of the polarity of a molecule, it's...

Bailey Giovanoli 1L

Hybridization occurs when the molecules don't have enough room in their orbitals to share electrons. For example, for CH4, carbon wants to form 4 bonds by sharing electrons to fill its octet. However, it has 2 electrons in the 2s orbital and 2 electrons in the 2p orbital, which makes it difficult f...

Bailey Giovanoli 1L

Does hybridization occur in all molecules? Dr. Lavelle gave the example of ammonia and CH4. Is there something special about these molecules? If so, what is it?

Bailey Giovanoli 1L

For some reason, this did not click in my head when Dr. Lavelle went over it in the lecture. However, this makes complete sense now. You guys are life savers!!

Bailey Giovanoli 1L

I like to have in my mind that whenever I see parenthesis, I cannot separate the molecule. This will help when you begin to see more complicated formulas.

Bailey Giovanoli 1L

If the molecules interacting are dipoles independently of one another, then there is a dipole-dipole interaction. An example of this is two HF molecules interacting.

Bailey Giovanoli 1L

Okay, thank you! I'll have to go back and rewatch because apparently I didn't take any notes on it.

Bailey Giovanoli 1L

In part b of 2E.11, the VSEPR formula was AX3E2. I was bewildered by this because it seemed to be an unfamiliar shape. I checked and realized that we never went over this in class. Although we did not go over this in the lecture, should I be expected to know that AX3E2 is considered "T-shaped&q...

Bailey Giovanoli 1L

Just to clarify, pi and sigma bonds occur in both non polar and polar molecules. In the lecture Lavelle showed N2, a no polar bond, and cis-Diochloroethene, A polar bond. Therefore, does this mean that a sigma bond occurs in every single bond, and a sigma and a pi bond occur in every double bond, an...

Bailey Giovanoli 1L

I find it helpful to remember that F has the highest ionization energy. From there, I know that almost every trend moves diagonally. So if F has the highest ionization energy, the trend Increases moves up and to the right.

Bailey Giovanoli 1L

So, essentially it is asking which has the most ionic character. Therefore, the one with the highest electronegativity different is the most ionic.

Bailey Giovanoli 1L

So, first start by recognizing that as the number of bonds increases and shortens, the strength of the bonds become stronger. A stronger bond is harder to break and takes more energy to break or melt. Also take a look at the types of bonds, for example, an ionic bond is much stronger and harder to b...

Bailey Giovanoli 1L

In section 2B on number 3 part d, I was wondering how Br could have three single bonds and two lone pairs. Wouldn’t this be an exception of the octet rule, or is this something else? Could someone please explain the concept to me. Thank you!!

Bailey Giovanoli 1L

I watched a video on youtube, which basically stated that there are certain atoms where the oxidation number is pretty much always the same. In oxygen's case, it is -2. From there, the video said that the oxidation number of the whole molecule should be equivalent to adding the oxidation numbers of...

Bailey Giovanoli 1L

Let me get this right, a dipole moment occurs whenever there is a covalent bond between two atoms that are not the same?

Bailey Giovanoli 1L

I too highly recommend the step up, workshop, and drop-in sessions. I would highly recommend attending Justin's workshops and step up sessions. He is very thorough and clear in the problems he does and works through. He doesn't give a worksheet but instead uses questions off of past exams, which has...

Bailey Giovanoli 1L

I watched a video on youtube, which basically stated that there are certain atoms where the oxidation number is pretty much always the same. In oxygen's case, it is -2. From there, the video said that the oxidation number of the whole molecule should be equivalent to adding the oxidation numbers of ...

Bailey Giovanoli 1L

hello, I looked into this, and I found on the internet that many students said that Dr. Lavelle sort of moves the grades around the average at the end of the quarter. I do not know if this pertains to this quarter or what it means about the midterm bump, that I also heard he is doing, but I hope thi...

Bailey Giovanoli 1L

Thanks, everyone! I found this very helpful. I figured out I had a calculation error on the one I was doing, so it makes sense why I wasn't approaching the problem correctly conceptually.

Bailey Giovanoli 1L

I was doing the Sapling homework, and I came across a problem involving oxidation numbers, #10 on Sapling. We have yet to talk about oxidation and oxidation numbers in lecture, correct? Is this something we will talk about in the future, or am I expected to pick up on it on my own?

Bailey Giovanoli 1L

Within a Lewis Structure, will the formal charge of an atom of that element always be the same? This will always be the same, regardless of different bond types, right? For Example in CO3 with a -2 charge, all of the oxygen atoms will have a formal charge of -1, regardless of one of the oxygens havi...

Bailey Giovanoli 1L

Exactly, this is the same method I used on sapling and got the correct answer. I do believe this is how to solve this type of question. It would be the only way that really made sense, you should see one line for each energy level transition.

Bailey Giovanoli 1L

So, in the solution to that problem, it states that when n, l, and ml are listed "regardless of the actual values an individual orbital can only hold two electrons." You can think back to in lecture how Dr. Lavelle showed how the p orbital is broken into an x, y, and z plane with each hold...

Bailey Giovanoli 1L

I was under the impression that the in the filling order for orbitals, 5s comes before 4d. Therefore, I would assume the electron configuration of Silver to be: Ag: [Kr] 4d^9, 5s^2 However, the solution manual has it as [Kr] 4d^10, 5s^1. Am I wrong and the 5s actually fills before the 4d shell or is...

Bailey Giovanoli 1L

Just to clarify, when looking at electron configurations, to determine whether it represents an excited or ground state you would just compare the configuration given to what you would expect the ground state to appear as, right? If it does not match with the ground state you would expect it is cons...

Bailey Giovanoli 1L

I'm not sure if this is an issue for you, but I always forget to take the square root to find the n instead of n^2. So, maybe check if that's an issue. If that's not the issue, I would be willing to help you further.

Bailey Giovanoli 1L

Yes, we have to memorize the general order and wavelength of the different types of electromagnetic radiation. My TA said that we should know the general wavelengths of the different colors of visible light as well. She sort of hinted at it coming up on the midterm.

Bailey Giovanoli 1L

My TA informed my class that we would need to know the electromagnetic spectrum on our own. She said we would not me be given wavelengths, so we should know off the top of our head. She recommended that we learn the different wavelengths for the different colors of visible light because it’s likely ...

Bailey Giovanoli 1L

Oh my gosh! Of course. I don’t know how I could forget that step. Thank you so much:)

Bailey Giovanoli 1L

On the post assessment quiz for the audio visual module on the photoelectric effect you are asked to find the energy required to remove an electron from one sodium atom. You are given the work function to be 150.6 kJ/mol. Isn’t the work function the same as the energy required to remove an electron?...

Bailey Giovanoli 1L

Okay that makes so much more sense. I tried it that way, but it didn’t work. I think it’s because I was using unrounded numbers the whole time. Thank you:)

Bailey Giovanoli 1L

On number 25 of the audio visual assessment for molar it’s and dilution you are asked: 25. 5.00 g of KMnO4 is dissolved in a 150.00 mL flask of water. If 20.00 mL of this solution is removed and placed in a new 2nd 250.00 mL flask and filled with water, what is the concentration of the solution in t...

Bailey Giovanoli 1L

Thank you! I’ve got it now!

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