CHEMISTRY COMMUNITY

VanessaZhu2L

I've tried to do this problem many times but I can't seem to get the correct answer. Can someone walk me through the steps of the problem? Thank you! The presence of a catalyst provides a reaction pathway in which the activation energy of a reaction is reduced by 49.00 kJ⋅mol−1 . Uncatalyzed: A⟶B Ea...

VanessaZhu2L

Can someone explain how to find the units of k? Does each order always have the same units or do we need to calculate it for each problem? Thank you!

VanessaZhu2L

When given a reaction, how do you determine what is being oxidized and what is being reduced?

VanessaZhu2L

Hi! Can someone explain the difference between k and K? Thank you!

VanessaZhu2L

Like what was said above, Organic Chemistry Tutor is really good and also Professor Dave Explains on youtube is really helpful to me to get the basic concepts!

VanessaZhu2L

I think that we'll be finishing the outlines by Wednesday, so Friday's lecture might just be a review!

VanessaZhu2L · Re: Final on 3/13 The final is on Sunday 03/14 from 9:30 am to 11:00 am!

The final is on Sunday 03/14 from 9:30 am to 11:00 am!

VanessaZhu2L

Yes, I think that Week 9 and Week 10 sampling are combined and is due friday of week 10 (03/12) instead of sunday!

VanessaZhu2L

I think that step up sessions go more step by step with the basics and concepts and workshops are more for if you understand the basics and want more review and help with solving problems.

VanessaZhu2L

I'm not completely sure, but I was able to view different threads and posts on chem community even though I wasn't logged into my account, I just couldn't make any posts. And also, when I look up questions, sometimes a chem community post pops up as one of the top search results, so I think you will...

VanessaZhu2L

I'm pretty sure the final is March 14, the sunday before final's week from 9:30am to 11:00am. For 14a during the final, we all took it at the same time, but with our TA. So it'll probably be like the midterms where zoom links for the final will be posted for each TA, and you just join the zoom when ...

VanessaZhu2L

I know that n is the number of moles in the reaction. How are you supposed to find this out when given a chemical reaction? Thank you!

VanessaZhu2L

For the reaction KClO3⟶KCl+32O2 assign oxidation numbers to each element on each side of the equation. for KCLO3, i got K is 1 and O is -2, which sampling said is correct. I thought that it would make Cl have an oxidation number of 1, but that isn't correct. Can someone explain to me how to get the ...

VanessaZhu2L

I'm taking BL right now and the time commitment isn't too bad! The only major thing we have to do outside of class/lab time are lab reports, and we usually have the whole week to complete it. Although since it is only six weeks, there might be two a week or longer reports. But it is pretty manageabl...

VanessaZhu2L

I was on the waitlist for this quarter in one of the last spots and I got in, so I think you will most likely be able to get in!

VanessaZhu2L

I am a little confused about the difference between H and q. I know that H is enthalpy and is a measure of heat, but how is that different from q?

VanessaZhu2L

Just to make sure, there won't be a lecture posted this friday right?

VanessaZhu2L

Yes, I think that it will all be proctored the same way!

VanessaZhu2L

it from from lecture 9 to last friday (lecture 16)!

VanessaZhu2L

We don't really know which specific problems are going to be on the midterm but if the problems in section 4D are listed in outline 3 or 4, I would definitely do them, just to make sure you understand all the topics that could possibly be covered in the test.

VanessaZhu2L

I'm not really sure where to start to solve this problem? Any help would be greatly appreciated! For a gaseous reaction, standard conditions are 298 K and a partial pressure of 1 bar for all species. For the reaction N2(g)+3H2(g)↽−−⇀2NH3(g) the standard change in Gibbs free energy is ΔG∘=−69.0 kJ/mo...

VanessaZhu2L

Thank you!

VanessaZhu2L

I feel the same way, I did all the assigned problems and still had a really hard time on the midterm. I think that step up sessions were helpful to me in grasping a lot of the concepts, and also watching youtube videos that explained the topics. Also, maybe going to office hours to review the midter...

VanessaZhu2L

These are all really helpful! Thank youu!

VanessaZhu2L

Yes, they usually do reviews but I would attend multiple just to get review on all the material!

VanessaZhu2L

Ahh that makes sense! Thank you!

VanessaZhu2L

At constant volume, the heat of combustion of a particular compound, compound A, is −3006.0 kJ/mol. When 1.569 g of compound A (molar mass =109.95 g/mol) is burned in a bomb calorimeter, the temperature of the calorimeter (including its contents) rose by 7.365 ∘C. What is the heat capacity (calorime...

VanessaZhu2L

For each reaction, identify another quantity that is equal to ΔH∘rxn. CH4(g)+2O2(g)⟶CO2(g)+2H2O(l) - 4×bond energy of C−H - enthalpy of formation of CO2(g) - enthalpy of combustion of CH4 - −4×bond energy of C−H Hi! Can someone explain how to do this problem? I don't really understand how to solve i...

VanessaZhu2L

I'm doing 14BL right now and its not too much work. We just have 15 minute lectures to watch each week and indivudual lab reports due and well as worksheets to complete with our group during lab time. It does really suck not being able to have any hands on experience and only learning conceptually h...

VanessaZhu2L

nevermind! I looked at the problem again and I get it now!

VanessaZhu2L

I was doing the textbook problems and I noticed that for some of the ICE tables in the calculations, they don't divide the moles by L while for other they do. I was wondering if anyone knew the difference for when to divide by L and when not to. Thank you!

VanessaZhu2L

Write the reaction quotient Q for (a) 2BCl3(g) + 2Hg(l) → B2Cl4(s) + Hg2Cl2(s) The answer in the solutions for this is 1 / BCl3^2. Can someone explain how they got this? I was also wondering if someone could explain what the difference is between Q and K and how to solve problems that ask for that. ...

VanessaZhu2L

I got an email from my TA that said that discussion and lecture on 1/29 will be canceled!

VanessaZhu2L

There is a Midterm 1 section on CCLE and if you click it, there is a list of links and you just find the link that corresponds with your lecture and discussion section.

VanessaZhu2L

Yes! I believe will will be using our phones for zoom like in 14A

VanessaZhu2L

ahh okay! That makes a lot of sense. Thank you guys so much!

VanessaZhu2L

HClO is a weak acid ( ka=4.0×10−8 ) and so the salt NaClO acts as a weak base. What is the pH of a solution that is 0.085 M in NaClO at 25 °C? In this problem, is it because they ask specifically about NaClO that you have to find kb first to solve the problem? I used ka and it was wrong so I just wa...

VanessaZhu2L

Yes, I think that we are allowed a periodic table and constants sheet and both are posted on the class website!

VanessaZhu2L

it is on friday, january 29 during the scheduled lecture time!

VanessaZhu2L

We probably will have some thermodynamics, but he will probably send an email soon about which outlines and which parts will be on the midterm

VanessaZhu2L

I would first start with making an ICE chart and solving for the initial molarity of 2SO3 by dividing the given moles by the given volume. Then you can start filling out your ice chart. The question gives you the final moles and by dividing that by the 3 L, you get the change in molarity/x. With th...

VanessaZhu2L

Hello! Can someone help explain how to do this problem? Thank you!

At a certain temperature, 0.980 mol SO3 is placed in a 3.00 L container.

2SO3(g)↽−−⇀2SO2(g)+O2(g)

At equilibrium, 0.130 mol O2 is present. Calculate Kc.

VanessaZhu2L

I think any calculator is fine!

VanessaZhu2L

Last quarter, he sent an email before the midterm that told us which outlines were going to be on the test, so he will probably let us know soon. But I think parts of outline three might be included too since he said that we already finished outline 2

VanessaZhu2L

If nothing works, you should definitely email your TA or Lavelle about it and see if they can figure out the issue

VanessaZhu2L

I don't think that topics in 14a will appear on the exam, but like the post before me said parts of the end of 14a might appear just because it overlaps with the content we are learning now. But Lavelle usually sends an email before tests on the topics that will be on the test, so if he does happen ...

VanessaZhu2L

It is due Sunday midnight at the end of week 2 on the 17th!

VanessaZhu2L

Yes, the only homework due are the problems assigned on sampling! But you get unlimited tries for each question and as long as you don't press the give up button, you will get full credit no matter the number of tries

VanessaZhu2L

I'm pretty sure that they are optional and just for practice if you need it!

VanessaZhu2L

I couldn't find it on CCLE either, but the zoom link will probably be posted soon!

VanessaZhu2L

Thank you so much for this!!

VanessaZhu2L

Its gunna be with our TA, but I saw somewhere that we might be put into breakout rooms with different proctors in the room, since there'll be a lot more people.

VanessaZhu2L

Yes, like the last two midterms, the final will also be multiple choice!

VanessaZhu2L

I think it is just a standard temperature, like room temperature. Since extreme temperatures can affect reactions and stuff, it just indicates that it isn't too hot or cold.

VanessaZhu2L

I was just wondering if we get any points from the course evaluations or if we have to do them for any credit. Thank you!

VanessaZhu2L

Yes, thank you! Also, does anyone know how to calculate oxidation number?

VanessaZhu2L

Can someone explain how to find coordination number for coordination compounds? Thank you!

VanessaZhu2L

Yea, Lavelle did not mention that we could use that sheet in his email, so we are probably not allowed to.

VanessaZhu2L

I was having trouble with that too! Thank you for the suggestion!

VanessaZhu2L

Yea, I would only use the resources that Lavelle listed in his email, which, like stated above are a calculator, constants and equations sheet, periodic table, and scratch paper. The ligand sheet is probably not permitted.

VanessaZhu2L

Yes, I think when you are just changing where the double bond is in the structure, all the resonance structure contribute equally to the resonace hybrid

VanessaZhu2L

Yea I think that all the 14A outlines will be covered for the final!

VanessaZhu2L

Yea! I think it is just for extra practice if you need it, not extra credit.

VanessaZhu2L

Yea, like what was said before, I think that the Lavelle wants to have the lectures recorded like this quarter, but it depends on if he can get permission to do it again and if he doesn't get sick. But he did suggest not to have any other classes overlapping with chem just in case.

VanessaZhu2L

I know we will probably have a lecture on Friday, but if we have discussion on Friday, will it be canceled due to Thanksgiving or will we still have to attend?

VanessaZhu2L

Yea, we do have sampling for week 7, but on CCLE it says week 7 and week 8 sampling it isn't due until sunday midnight of week 8

VanessaZhu2L

Yea! I'm pretty sure we'll get our midterm grades by next week!

VanessaZhu2L

How do you find the differences in the electronegativities? Is it based on where they are on the periodic table?

VanessaZhu2L

Also for ion or nonpolar molecules. How can you tell from like the chemical formula which molecule is ionic or covalent and if there are partial charges or not.

VanessaZhu2L

How can you identify whether or not a covalent bond is polar or not? Are there certain elements that that always create polar covalent bonds? Thank you!

VanessaZhu2L

Yes, it covers the rest of Outline 2 and all of Outline 3!

VanessaZhu2L

For that one, I has P in the middle and three oxygens single bonded to the phosphate. Each oxygen has three lone pair and a negative charge. The phosphate in the middle also has one lone pair.

VanessaZhu2L

Can someone explain how you know the number of bonds an element can have? I thought that nitrogen could only have three bonds but when doing sampling, they said it could have four. So I was wondering how you figure out the number of bonds an element can have? Thank you!

VanessaZhu2L

Is it better to enroll in 14B during the first enrollment or will it be okay to save it until the second enrollment? I'm not sure how fast the class will fill up and I want to see which is the better option. Thank you!

VanessaZhu2L

I was wondering what the difference was between induced dipole and dipole and why induced dipole has a weaker bond.

Thank you!

VanessaZhu2L

Yes, I agree that going to a step up or workshop session will be very helpful if you miss discussion. But I don't think missing discussion will have a negative impact on your grade.

VanessaZhu2L

Can someone explain what delocalized electrons are? I don't really understand. Thank you!

VanessaZhu2L

He also has outlines of the different topics on the class website and what textbook problems to complete for those topics. I assume for now that the second part of outline 2 and probably outline 3 will be on the second midterm. Maybe more but not sure yet.

VanessaZhu2L

I'm doing LS7C and chem 14a right now and I think that the homework for bio is definitely more time consuming. We have readings due before every class which can take a while to read, but the class itself isn't too challenging if you do the readings and understand the clicker questions in lecture. Bu...

VanessaZhu2L

Hi! Can someone explain for the SO4^2- Lewis Structure why S is able to have 6 bonds? Thank you!

VanessaZhu2L

Hi! Can someone explain what the ml atomic number represents and how many electrons are there?

Thank you!

VanessaZhu2L

Hi! I am a little confused about the different types of orbitals. Can someone summarize the differences between the s, p, d, and f orbitals?

Thank you!

VanessaZhu2L

For 25, when finding the energy of the photon and electron, the solution gives two different ways to solve it. For the photon, they use E=hv and c=vλ and for electron, they used λ=h/p and e=1/2mv^2. I was wondering why they used the two different methods and how you know which equations work with th...

VanessaZhu2L

Thank you!

VanessaZhu2L

Hi can someone help me solve this? I got the work function, but I don't understand how to do the second part. Thank you! When a metal was exposed to photons at a frequency of 1.23×1015 s−1, electrons were emitted with a maximum kinetic energy of 3.70×10−19 J. Calculate the work function, Φ, of this ...

VanessaZhu2L

Are the sampling Hw problems in the correct order now or are they still shuffled randomly?

VanessaZhu2L

I noticed that sometimes to solve a problem, you would need to combine one or two equations together to be able to get the answer. I was wondering if anyone had any advice to how to recognize when you need to do that. Also if anyone had any advice on how to know which equation should be used for whi...

VanessaZhu2L

For the miderms, are we supposed to have two cameras for our face and our desk, or is it just one for our desk?

VanessaZhu2L

Yes, thank you I realized he answered it later in the lecture, i just didn't watch far enough lol

VanessaZhu2L

Hi! I had a question about the example in class about if the car has any measurable wavelike properties. How do you know if it does or not? Is there a certain mass that the object cannot exceed in order for it to be considered to have wavelike properties or is it just that it has to be an extremely ...

VanessaZhu2L

Can someone help explain this? Thank you! The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation? To what region of the electromagnetic spectrum does this wavelength correspond (i...

VanessaZhu2L

Yea I think the one on the website should be okay

VanessaZhu2L

Does anyone remember the password for the 14A website? I looked everyone on CCLE and I don't remember where we got the password. Thank you!

VanessaZhu2L

I had a quick question about the midterms. Will we be allowed to have a printout of the periodic table for like molarity questions? Or will they be provided on the exam. Same with things like the speed of light, plank's constant, etc. Are we expected to memorize all of that? Or can we have a sheet w...

VanessaZhu2L

Hi! Can someone explain this? Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. Answer the following three questions. A. What is the kinetic energy of the ejected electron? B. How much energy is required to...

VanessaZhu2L

Hi! Can someone explain how to solve this? Thank you!

A solution is prepared by dissolving 55.1 g of KCl in approximately 75 mL of water and then adding water to a final volume of 125 mL. What is the molarity of KCl(aq) in this solution?

VanessaZhu2L

Hi! Can someone explain how to solve this? According to the following equation, 0.750 g of C6H9Cl3 is mixed with 1.000 kg of AgNO3 in a flask of water. A white solid, AgCl, completely precipitates out. What is the mass of AgCl produced? C6H9Cl3 + 3AgNO3 ---> AgCl + C6H9(NO3)3. Molar Mass: C6H9Cl3 (1...

VanessaZhu2L

Ohh okay! That makes sense. Thank you guys so much!

VanessaZhu2L

Thank you so much for the advice! This was very helpful :)

VanessaZhu2L

I don't really understand how to solve this? How do I compare the Co2 and CaCo3?

How many moles of CO2(g) are produced when 1 kg of CaCO3(s) is used to neutralize an acid spill? The equation for the reaction at 1 atm and 25 degrees C is:

CaCO3(s) + H2SO4(aq) ---> CaSO4(s) + CO2(g) + H2O(l)

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