CHEMISTRY COMMUNITY

Deena Doan 2F

For number 5, why is the first reaction flipped if it has a higher standard cell potential? Doesn't that mean it's the cathode?

Deena Doan 2F

Lavelle just sent an email out about the format of the test and it's going to be through CCLE!

Deena Doan 2F

We probably would have to print out the exam once Dr. Lavelle emails us with more information.

Deena Doan 2F

He said he was going to send more detailed instructions on Saturday, but the time frame is probably going to be 3 hours since it's going to be short, but he may give us another hour to prep the exam, etc.

Deena Doan 2F

For this one, I had to think about it logically like the person above said. If you want to lower the pH, you have to add an acid. That's why A and C were the answers since they were both acidic.

Deena Doan 2F

the one that has a higher (more positive) value is usually the one that is reduced aka the cathode

Deena Doan 2F

Dinitrogen pentoxide, N2O5, decomposes by a first-order reaction. What is the initial rate of decomposition of N2O5 when 3.45 g of N2O5 is confined in a container of volume 0.750 L and heated to 65 8C? For this reaction, k1= 5.2x10^-3 s^-1 in the rate law (for the rate of decomposition of N2O5). How...

Deena Doan 2F

I would probably still study it a little bit, but there might not be a heavy emphasis because, in the email, he did say it was going to be shorter so that might mean he'll focus more on the new material.

Deena Doan 2F

Are the rest of the discussions going to be on Zoom or are they just canceled?

Deena Doan 2F

What is the rate-limiting step?

Deena Doan 2F

How will Test 2 be distributed back if classes are online?

Deena Doan 2F

thank you Lyndon for your service and help!!! i was wondering if there is any way you could do a live stream or Zoom this session.

Deena Doan 2F

How do you determine whether it's kinetics or thermodynamics in regard to controlling a reaction? Is there a "hack" or a quick way to determine?

Deena Doan 2F

G=-nFE
G=-RTlnK
These are the 2 equations you'll use.

Deena Doan 2F

I know on Test 2 we didn't need to know how to derive it, but do you think we will have to know how to derive it for the final?

Deena Doan 2F

Since it is given in cell potential, that means that it is a reduction. So, to get oxidation, you flip it.

Deena Doan 2F

1. find the half-reactions
2. balance O
3. balance H
4. balance the charges by adding electrons

If you go through the textbook, it has a really helpful example that shows you step by step!

Deena Doan 2F

I was going over Test 1 to practice for the final and I was wondering if someone can help me solve this problem.

The pH of a 0.010 M solution of acetic acid is 3.37. What are Ka and percent ionization? I got the percent ionization right, but not the Ka.

Deena Doan 2F

How do I figure out the order of a reaction?

Deena Doan 2F

When do we use the Arrhenius equation? Like what are some keywords in a question to know whether or not to use this equation?

Deena Doan 2F

It's most likely going to cover all concepts, but there probably is going to be a heavier emphasis on kinetics and thermo.

Deena Doan 2F

Sometimes, watching Youtube videos can be very helpful along with rereading the textbook.

Deena Doan 2F

I can. What's your email?

Deena Doan 2F

It's usually joules per mole

Deena Doan 2F

I'm pretty sure it will tell us in the problem.

Deena Doan 2F

A tin electrode in 0.015 m Sn(NO3)2(aq) is connected to a hydrogen electrode in which the pressure of H2 is 1.0 bar. If the cell potential is 0.061 V at 25 8C, what is the pH of the electrolyte at the hydrogen electrode?

How do I derive an equation for the redox equation from this information?

Deena Doan 2F

How do you find the n in that equation?

Deena Doan 2F

I think it's because you have to look at the net charge of the overall molecule instead of the charges of the components of the molecule.

Deena Doan 2F

The overall molecule has a charge of -1 and we already know that oxygen has a charge of -2 and when you multiply by 4, you get a charge of -8. So, in order to get that -1 charge, Mn has to have a 7+ charge.

Deena Doan 2F

I'm pretty sure the song is "Whatever It Takes" by Imagine Dragons!

Deena Doan 2F

4H.5 Which substance in each of the following pairs would you expect to have the higher standard molar entropy at 298 K and 1 bar? Explain your reasoning. (a) Iodine vapor or bromine vapor; (b) the two liquids cyclopentane and 1-pentene (see structures); (c) ethene (ethylene) or an equivalent mass o...

Deena Doan 2F

4D.1 Carbon disulfide can be prepared from coke (an impure form of carbon) and elemental sulfur: 4 C(s) + S8(s) -> 4 CS2(l) delta H° = 358.8 kJ Calculate the heat absorbed in the reaction of 197 g of carbon with an excess of sulfur. Can someone walk me through this and break it down conceptually?

Deena Doan 2F

4C.11 How much heat is needed to convert 80.0 g of ice at 0.0 8C into liquid water at 20.0 8C (see Tables 4A.2 and 4C.1)?

Can someone explain this problem to me?

Deena Doan 2F

(a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0 C to the boiling point of water, 100.0 C. (b) What percentage of the heat is used to raise the temperature of the water? (See Table 4A.2.) How do I solve this?

Deena Doan 2F

I can send you the notes! What's your email?

Deena Doan 2F

Knowing both delta u or delta h and delta s of a system provides info on how the system will change

Deena Doan 2F

Can someone explain the difference between a closed and isolated system?

Deena Doan 2F

Some UA's post their worksheets on Chem Community, so you can probably search up worksheets or review to find them!

Deena Doan 2F

How do I know which method to use? Are there like key words/terms that will help me determine which method to use when it comes to solving the problem?

Deena Doan 2F

Yeah, I can! What's your email?

Deena Doan 2F

Most times, you do get partial credit if it makes sense. But, it also depends on the grader.

Deena Doan 2F

6D.3 (a) When the pH of 0.10 m HClO2(aq) was measured, it was found to be 1.2. What are the values of Ka and pKa of chlorous acid? (b) The pH of a 0.10 m propylamine, C3H7NH2, aqueous solution was measured as 11.86. What are the values of Kb and pKb of propylamine? How do you get the concentration o...

Deena Doan 2F

5I.33 A sample of ammonium carbamate, NH4(NH2CO2), of mass 25.0 g was placed in an evacuated flask of volume 0.250 L and kept at 25 8C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The reaction is NH4...

Deena Doan 2F

5I.13 (a) In an experiment, 2.0 mmol Cl2(g) was sealed into a reaction vessel of volume 2.0 L and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 5G.2 to calculate the equilibrium composition of the mixture. (b) If 2.0 mmol F2 was placed into the reaction vess...

Deena Doan 2F

When a problem is asking to write an expression for K, how do I know whether to use concentration or partial pressure?

Deena Doan 2F

I know that they are solved the same way but what is the difference between solving for K and solving for Q?

Deena Doan 2F

it's when all reactants and products are in the same phase.

Deena Doan 2F

How do you use an ICE table?

Deena Doan 2F

What is the difference between Kc and Kp?

Deena Doan 2F

I'm pretty sure they count at the end, but it might depend on your TA.

Deena Doan 2F

You have to draw it out to figure out where the lone pairs are.

Deena Doan 2F

You use bis, tris, etc when it comes to en and dien and edta.

Deena Doan 2F

Do sig figs only count after the decimal when it comes to pH?

Deena Doan 2F

I'm pretty sure both forms are acceptable, but I would probably do it alphabetically just in case.

Deena Doan 2F

it's polar

Deena Doan 2F

Does anyone have a good way of memorizing the order of naming?

Deena Doan 2F

The organic chemistry tutor is really good at explaining concepts.

Deena Doan 2F

There is a possibility we might have to know the structure of it as well because I think I read it somewhere on Bruinwalk.

Deena Doan 2F

Does anyone know what topics will be strongly emphasized on the final?

Deena Doan 2F

I would read the sections that the homework problems are from. I think sections are also listed on the syllabus and the outlines. For studying, I recommend doing the homework problems and Youtube videos for extra practice!

Deena Doan 2F

Youtube videos are super helpful and so are the step-up sessions! The UA's are really good at explaining concepts and they usually go through practice problems as well.

Deena Doan 2F

Yes. Typically, elements in period 3 and above are able to have an expanded octet.

Deena Doan 2F

I'm sad. All of the good chemistry jokes argon :(

Deena Doan 2F

When will test 2 scores be out on myucla? Are we getting our tests back this week?

Deena Doan 2F

What exactly is a ligand?

Deena Doan 2F

valence shell electron pair repulsion model

Deena Doan 2F

Can someone explain this problem to me?

3F.3 For which of the following molecules will dipole–dipole interactions be important: (a) CH4; (b) CH3Cl; (c) CH2Cl2; (d) CHCl3; (e) CCl4?

Deena Doan 2F

Also, does anyone know how many questions will be on the test?

Deena Doan 2F

Does anyone know how many points test 2 will be worth?

Deena Doan 2F

How do you identify the different forces between molecules?

Deena Doan 2F

Hi,
Does anyone know if it is better to take Chem 14B and Chem 14BL together or Chem14C and Chem14BL together? Or does it not really matter?

Deena Doan 2F

Hi,
How can I use the periodic table to determine whether one element has higher polarizability compared to another element?

Deena Doan 2F

Will we be getting our tests back in our discussion section next week?

Deena Doan 2F

It's preferred because it is easier to understand conceptually with the way he taught us in class.

Deena Doan 2F

So... when's the midterm?

Deena Doan 2F

Hi,
Are we allowed to actually use Rydbreg's equation or do we have to solve these types of problems the way Lavelle taught us in class?

Deena Doan 2F

Hi,
What does it mean when it says to draw the lowest energy lewis structure?

Deena Doan 2F

Hi,
Does anyone know we have to use formal charge to check every lewis structure diagram we do on the midterm?

Deena Doan 2F

it's 10 m/s because it's a range from -5 to 5 m/s

Deena Doan 2F

The TA's and UA's typically have a list of topics they are going to go over and they go over the concepts while including practice problems as well. They're very helpful! Highly recommend.

Deena Doan 2F

I think it can be from both chemical bonds and the quantum world, but I would suggest emailing your TA just to make sure.

Deena Doan 2F

How come the electron configuration for tungsten is [Xe]4f14 5d4 6s2 and not [Xe]4f14 5d5 6s1? Why didn't it follow the same rule as silver did?

Deena Doan 2F

Hi! There is also this Youtuber called Tyler Dewit who has a video about electron configurations that is very helpful as well!

Deena Doan 2F

Hi,
Is this week's homework on just chemical bonds or can it also be from the quantum world?

Deena Doan 2F

1) move left
2) move right
3) If it has a positive charge (aka a cation), it loses an electron.
4) If it has a negative charge (aka an anion), it gains an electron.

Deena Doan 2F

Hi,
Does anyone have any tricks or recommendations to help memorize the trends in the periodic table and also the characteristics of nonmetals/metals/metalloids?

Deena Doan 2F

Does anyone know if the Fundamentals section is going to be on our midterm?

Deena Doan 2F

Hi,
Why can't there be parallel spins? Also, how do you know whether to start it up or down for the spins?

Deena Doan 2F

Hi,
In class, Lavelle went over some examples for the orbitals and he did Scandium as an example, but I am still a little confused on how why it is [Ar] 3d1, 4s2 and not the other way around.

Deena Doan 2F

Hi! I definitely recommend everything else everyone has said so far! For me, what works the best is doing everything he assigns and joining study groups! They are so helpful and collaborating with other students makes it easier to understand. I also watch Youtube videos; there is this one guy named ...

Deena Doan 2F

Hi, Can someone explain why part a is false? I read the solutions manual, but I am still a little bit confused. Thank you! Which of the following statements are true for many-elec- tron atoms? If false, explain why. (a) The effective nuclear charge Zeffe is independent of the number of electrons pre...

Deena Doan 2F

No, it won't be tested.

Deena Doan 2F

Hi,
Can someone explain the difference between these two? Like what does it mean if something has wavelike properties but not particle-like and vice versa?

Deena Doan 2F

Hi,
Can someone please explain this problem to me? I don't understand it.

What is the minimum uncertainty in the speed of an electron confined within a lead atom of diameter 350. pm? Model the atom as a one-dimensional box with a length equal to the diameter of the actual atom.

Thank you!

Deena Doan 2F

I was just wondering if he expected us to know the constant in this problem or will he give it to us on tests?

Deena Doan 2F

I'm not sure what exactly we have to know, but there is a table on F30 that has some common ones listed so I would probably want to know those.

Deena Doan 2F

it's the least amount of sigfigs that matter

Deena Doan 2F

Hi,
I'm pretty sure he is going to give us the formula, but I would brush up on the formulas for some basic compounds like nitric acid, etc just in case.

Deena Doan 2F

Hi,
Can someone walk me through on finding the formula for magnesium sulfate heptahydrate and why 7 H2O is a part of the formula mass?

Deena Doan 2F

Hi, does anyone know if he expects us to know how to write formulas/compounds on the test? Was just wondering because some of the homework problems asked us to do so.

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