CHEMISTRY COMMUNITY

Prasanna Padmanabham 4I

I am really nervous and want to find out soon too, but in the email Dr. Lavelle sent earlier today, he said that he was updating Chem community scores on Thursday, so I imagine he will update all scores at the same time (final too)...but IDK...but soon hopefully...

Prasanna Padmanabham 4I

Sine it says pi comes from ATP, the two concentrations cancels and K depends on [ADP] only. Maybe I am wrong about how I interpreted this problem, but I assumed that since all the Pi came from ATP, I assumed it meant that it only came from ATP that was broken into ADP...so Pi = ADP concentration......

Prasanna Padmanabham 4I

I tend to forget stressful scenarios, so I don't remember what was on the final lol, but I believe I used the Van't Hoff equation. The equation relates delta H, two equilibrium and two different temperatures together. I used information given in the previous equation for the K values and T values. U...

Prasanna Padmanabham 4I

Shanzey wrote:I liked drawing Lewis structures!

Same!

Prasanna Padmanabham 4I

Hi Everyone, I am super stuck on this problem. I would appreciate it if someone could please give me a detailed explanation about how to solve this problem. Calculate the time required for each of the following second-order reactions to take place: (a) 2A --> B + C, for the concentration of A to dec...

Prasanna Padmanabham 4I

It's an open book final...

Prasanna Padmanabham 4I

I would assume that we still have normal class because there hasn't been any emails from him yet I'm pretty sure there will be bad consequences for a professors that hold normal, in-person classes. My friend's RA sent a text with information on reporting professors that are holding in person classe...

Prasanna Padmanabham 4I

Thank you so much Lyndon! I appreciate all the time you have put into us even though you had a really busy schedule with upperdivs and other commitments.

Prasanna Padmanabham 4I

alex_4l wrote:Does anyone have an idea if it will be proctored?

I read that for the online versions of the finals teachers can enforce students to turn on their webcam and audio.

Prasanna Padmanabham 4I

What edition textbook are you using? Part b on 6D.15 for me is asking about AlCl3...

Prasanna Padmanabham 4I

If you genuinely understand how to do all the homework problems along with the small detials he mentions in lecture, you should be fine for the final. Emphasize the "small details in lecture" I would also go through the outlines...sometimes there are things that aren't tested/asked for on...

Prasanna Padmanabham 4I

Adding on, can we take the final from home or do we need to be on UCLA wifi?

Prasanna Padmanabham 4I

All the Chapter 5 concepts/problems

Prasanna Padmanabham 4I

VioletKo3F wrote:Would there be any conceptual ideas that we should know before the test?

I would go through his outlines. For 14A test2, there were definitely a lot of "conceptual" questions in addition to the "math-heavy" questions.

Prasanna Padmanabham 4I

Isn't Cu2+ being reduced to Cu? So shouldn't the textbook Standard Cell Potential be +0.34 as the textbook says? Isn't the left side of the cell diagram always the cathode (reduction half-reaction)?
I'm really confused now...

Thank you?

Prasanna Padmanabham 4I

nshahwan 1L wrote:Should there be any specific examples of salts that are in salt bridges that we should be aware of?

NaCl is an easy one to remember...the salts are there to balance out the charge and they don't react with the reactants or products.

Prasanna Padmanabham 4I

Vinita Saxena 2I wrote:Yup, cathode is reduced and anode is oxidized!

My TA taught us an easy way to remember this: "an ox" for anode is oxidized and a "red cat" for reduction happens at the cathode.

Prasanna Padmanabham 4I

Here is a prior post I found on Chem Community that goes into every single detail: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=11377 that solves this question step by step. But in short, you would 1) write out the Cl and the S2O3 half-reactions separately to first figure out the change in ch...

Prasanna Padmanabham 4I

Yes, when a battery is dead, the system has reached equilibrium -- though I'm wondering now if it's possible to 'revive' a battery or replace its galvanic cells concentration gradient? Isn't this done by recharging it by sending an electric current in the reverse direction...isn't that basically wh...

Prasanna Padmanabham 4I

All of the electrochemistry and the chapter 5 units in the Thermodynamics outline.

Prasanna Padmanabham 4I

Yes, it means that the reverse process is spontaneous...

Prasanna Padmanabham 4I

Anode and cathode are defined that way...electrons go from anode to cathode...

Prasanna Padmanabham 4I

So you would just flip the signs because the reverse is occurring...

Prasanna Padmanabham 4I

[/quote]
This would then affect Q in the Nernst equation right?[/quote]

Yup because Q is the concentration of reactants/products

Prasanna Padmanabham 4I

Khan Academy is also really good.

Prasanna Padmanabham 4I

When the Gibbs Free Energy is negative it means that the forward reaction is spontaneous while if it is positive, it means that the reverse reaction is spontaneous.

Prasanna Padmanabham 4I

Based on his syllabus and last quarter (14a), I don't think he curves to help a B+, A-, A student...I believe the "curve" he refers to on his syllabus is mostly for students in the C (getting a 50% to pass the class)...but I will say that the midterm was hard and I do hope things are diffe...

Prasanna Padmanabham 4I

Oxidation numbers are basically the charges on an atom/ion...do you have a specific question/reaction in mind? By the way, I found this really helpful article on Khan Academy https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichiome/types-of-chemical-reactions/a/oxidation-number if...

Prasanna Padmanabham 4I

Yes, fusion does mean melting and enthalpy is positive. For the other way, freezing, change in enthalpy is the same, but you change the sign and it becomes negative.

Prasanna Padmanabham 4I

Electrons are really important in electrochemistry and writing out the electrons helps you figure out what is being oxidized and reduced and really understand what is happening to the electrons in the reaction...It will make more sense when Dr. Lavelle goes into more details and we started doing mor...

Prasanna Padmanabham 4I

Thank you!

Prasanna Padmanabham 4I

Hello, I am really stuck on this problem. I would super appreciate it if someone could please help me solve it. 4I.5 Suppose that 50.0 g of water at 20.0 8C is mixed with 65.0 g of water at 50.0 8C at constant atmospheric pressure in a thermally insulated vessel. Calculate ΔS and ΔS (total) for the ...

Prasanna Padmanabham 4I

For gases, the change in enthalpy is defined by that equation. This is because when gas is produced work is done to clear the other gases so the enthalpy is lower than the internal energy. This is explained in detail on pg 274 in the textbook (4D.2)

Prasanna Padmanabham 4I

Alexis Robles 2k wrote:when should we use the m/n in the equation?

Did mean to type: q=n*CdeltaT

If so, n refers to mols while m refers to grams...you would use whatever units the question asked for...

Prasanna Padmanabham 4I

The Boltzmann equation is giving the residual entropy of the system. Entropy is the amount of "disorder" and the Boltzmann equation is sort of giving a statistical answer of all the possible orientations and positions of all the molecules in the system.

Prasanna Padmanabham 4I

Thank you guys for your replies! I used the answer key at the back of the book (I don't have the solution manual) and it said 90 * 10^2 J...I think that the answer key in the book is wrong since the solution manual also says 490.

Prasanna Padmanabham 4I

I feel like it wouldn't hurt to know...there were a few graph questions on the 14A midterm and final last quarter...

Prasanna Padmanabham 4I

Hello, I got the first part of this question right, but not the second, I was curious if someone could help me figure out what I'm missing. Thank you! The internal energy of a system increased by 982 J when it was supplied with 492 J of energy as heat. (a) Was work done by or on the system? (b) How ...

Prasanna Padmanabham 4I

Ben 1B wrote:Does anyone know if we will be able to take a practice midterm before the actual midterm?

The UAs made a practice midterm for us this quarter. Search up Pizza Rolls and you should find it.

Prasanna Padmanabham 4I

You should watch this video for an introduction to internal energy and U

https://www.khanacademy.org/science/physics/thermodynamics/laws-of-thermodynamics/v/more-on-internal-energy

Prasanna Padmanabham 4I

Does anyone know if all the thermochemistry and thermodynamic equations will be supplied on the midterm? Dr. Lavelle is usually really nice about the equations and provides everything you would need. I'm pretty sure he uses the same equation sheet for all the tests so you can take a look at test 1....

Prasanna Padmanabham 4I

The outlines are a great resource to find practice problems and use as a study plan/guide. Additionally, attending all the (one per each topic) review sessions will also help you figure out what material will be covered and where you are. Sometimes the textbook can feel a bit too broad. I'm pretty s...

Prasanna Padmanabham 4I

I think about the same as I think about endothermic or exothermic reactions. If heat is being released by the system, enthalpy (delta H) is negative and like that, if the system is doing work, then the work is negative. If the system needs heat then the enthalpy (delta H) sign is positive, and if so...

Prasanna Padmanabham 4I

hopefully Lyndon, the UA will make us a practice midterm :/...
The one he made for 14A last quarter was really helpful and I really appreciated it :).

Prasanna Padmanabham 4I

I found a really interesting article/video in my newsfeed. Recently, scientists published their experiment showing/recording of chemical bonds forming and breaking. Here is the link to the article if you all want to watch the too :) https://www.sciencenews.org/article/dance-two-atoms-reveals-chemica...

Prasanna Padmanabham 4I

It really depends on what information you are given, I feel like for most problems this is how I've been dealing with it...
1) convert pKa to Ka
Ka = 10^(-pKa)
2) write Ka concentration out and figure out [H+]
3) plug into pH = -log [H+]

Prasanna Padmanabham 4I

Follow up question: I am still very stuck on this problem, can someone please post a step-by-step of the solution?
Thank you so much!

Prasanna Padmanabham 4I

I would assume that i is neither since the moles are equal on both sides. The pressure increases with the volume decreasing so the chemical reaction would favor the side with less moles but that is not an option. I didn't see this at first either, but the I2 in the products has an (s) next to it, s...

Prasanna Padmanabham 4I

Well, if Ka is less than 10^-3, then you are usually safe to approximate. In the end, though, you typically need to make sure that x is less than 5% of the initial concentration. If it is less than 5%, you are good, if it's not, you need to redo the problem. For the test specifically, I'm not sure i...

Prasanna Padmanabham 4I

Hi Everyone, I am having a really hard time with this problem. I would appreciate if someone can please let me know what I'm doing wrong. 6D.15 Calculate the pH of (a) 0.19 m NH4Cl(aq); (b) 0.055 m AlCl3(aq). For part B) is the equation: AlCl3 <==> Al (OH-)3 + 3HCl. The 3HCl then dissociates complet...

Prasanna Padmanabham 4I

Dr. Lavelle, in the lecture, talked about how Kc should technically be measured by how much "activity" is occurring in the equation. So how much activity that is produced by the forward reaction and how much activity is produced by the reverse reaction. Since it is a bit hard to measure th...

Prasanna Padmanabham 4I

I was doing a homework problem and I was using my calculator's quadratic function to solve the Kc equations. The funny part, I guess, is that my x value was so small that when I subtracted it from the initial value the first two digits/numbers were still the same. When you have two (or three) signif...

Prasanna Padmanabham 4I

The volume was halved. So initially, you had 0.020 mols/Liter and now you have 0.020 mols/0.5Liters = 0.040 M. Equilibrium concentration, values when trying to find Kc, deal with values in mols/Liter or molarity.

Prasanna Padmanabham 4I

I have a followup question: Why did you all decide to set x = to change in equilibrium for H2 or Cl2, and 2X = change in HCL instead of saying x = change in HCL and 0.5X = change in H2 and Cl2? I did it the second way and I got the wrong answer. I'm trying to understand conceptually why my way is wr...

Prasanna Padmanabham 4I

Hello,
If there was an equation with liquids and gases in products and/or reactants side, how would you write Kc? Would you include both liquids and gases in it or only the gases or do you write two separate equations?

Prasanna Padmanabham 4I

Thank you!

Prasanna Padmanabham 4I

that's confusing...hmm...did it say millimolars? I'm interested in an answer too...

Prasanna Padmanabham 4I

This equation is super versatile. If you know a few variables and you are trying to figure out how to represent ideal gases differently, then, you can just rearrange the equation. For example, if you have the pressure of a gas, but want to know what the concentration of the gas is you just need to r...

Prasanna Padmanabham 4I

Hello
I was in Dr. Lavelle's class (14A) last quarter, and I was curious if I had to do something to "update" my account to make sure I'm getting credit for participating in 14B class.
Thank you!

Prasanna Padmanabham 4I

I can answer why there is no change from the increase in pressure. Usually, in a Kp equation, the partial pressure is representative of the number of mole/concentrations of a substance at a certain temperature and volume. You can think of it as how much "stuff" is there increases with pres...

Prasanna Padmanabham 4I

c) if one starts with a higher pressure of reactant, the equilibrium constant will be larger This is false because the equilibrium constant will stay the same for reactions happening at the same temperature. Having a "greater pressure" of the reactant will affect or cause a shift to the le...

Prasanna Padmanabham 4I

According to the textbook, for any anion inside the [ ] (so any anion directly bonded to the central metal cation), the ending should be an -ato or an -ido or an -ito. For example, the Chloride anion is written as chlorido.

Prasanna Padmanabham 4I

I believe its because there is a negative charge on the BrO- molecule.

Prasanna Padmanabham 4I

I'm pretty sure many of the elements have Latin names or come from Latin words. You just need to memorize that Iron is written as ferrate if a coordination molecule is negative.

Prasanna Padmanabham 4I

Those are the same answers I got (and I got the answer correctly). En= Eupper - Elower, but En= - hR/n^2, so when you plug it in you would get: En = -Eupper - (-E lower) so En=-Eupper + Elower. Since as n increases, En get closer to 0, and as n gets smaller, En decreases (remember big negative numbe...

Prasanna Padmanabham 4I

When the equation is NH4+ + H2O --> NH3 + H3O+
You notice how the NH4 is donating a Hydrogen. pH is the -log[H+] so as the concentration of H+ increases, then the pH decreases. NH4+ is a proton donator and therefore the concentration of H+ increases which then decreases the pH.

Prasanna Padmanabham 4I

Cl- does not affect the pH of a solution because Cl- is a really stable atom; it does not need to bind to a Hydrogen. While NH3- is a weak base so it's conjugate acid, NH4 will lose a few Hydrogens in the NH4 and act as an acid by donating its extra Hydrogen.

Prasanna Padmanabham 4I

I feel you! I do the easier problems first because it makes me feel better (psychologically) and then I try to the harder problems. Think about what you do know because chances are you do know a lot. Maybe, if you can, identify what chapter the question is from and write down all the equations you k...

Prasanna Padmanabham 4I

VSPER stands for Valence shell electron pair repulsion theory. While lewis structures are helpful to figure out single/double bonds and the number of lone pairs etc. VSPER takes electron pair repulsions into considerations and allows us to think about the 3D shape of the molecule.

Prasanna Padmanabham 4I

Do you have a specific example or a specific problem you are stuck on? I'm not quite sure how to answer your question broadly...

Prasanna Padmanabham 4I

Those with resonance structures are weaker acids because it is harder for the hydrogen atoms to "break off" because the negative formal charge is distributed throughout so resonance structures are more stable.

Prasanna Padmanabham 4I

HPO4(2-) as an acid: PO4(3-) (conjugate base)
HPO4 (2-) as a base: H2PO4 (-1) (conjugate acid)...

Prasanna Padmanabham 4I

I know this video isn't really for the exact same molecule, but they are similar and you can use the same "technique" to analyze the polarity of CH2Br2

[youtube]https://www.youtube.com/watch?v=As-hcYY8Yaw[/youtube]

Prasanna Padmanabham 4I

In example 6A.2 in the textbook, the question is: Barium hydroxide is a base that is sometimes used for titrating acids. When using it, you need to know the actual concentration of hydroxide ion in the solution. What are the molar concentrations of H3O1+ and OH2- in 0.0030 m Ba(OH)2(aq) at 25 C? In ...

Prasanna Padmanabham 4I

The dipole moment is basically when a partially negatively charged atom in a polar covalent bond is attracted to another positively charged thing (usually the positively charged atom of another polar covalent bond or a cation). This isn't like a bond, but there is a very weak, but still significant ...

Prasanna Padmanabham 4I

I believe bond order just refers to the number of bonds between two atoms (single bonds, double bonds, triple bonds etc.) so I would just draw a lewis structure and count... https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Th...

Prasanna Padmanabham 4I

I guess it officially described as being "polar covalent" but its super ionic in character.

Prasanna Padmanabham 4I

I would imagine so, but I would be interested in knowing how he curves the class considering the fact that the average score on the last midterm was like a high 70%...

Prasanna Padmanabham 4I

I understand, but what sort of specific questions might he ask? What textbook problems should I do? I feel like we did a lot of theory so I'm not sure what sort of questions I should be prepared for...

Prasanna Padmanabham 4I

Can someone please direct me towards what lessons/pages I should read to prepare for Test 2?

Prasanna Padmanabham 4I

Well my discussion is on Wednesday and I'm really nervous....can someone please post specific textbook sections we should study for the test?

Thank you!

Prasanna Padmanabham 4I

It looks like your Hydrogen is bonded directly to the Chlorine, but its almost always attached to an Oxygen with acids and (bases too I think)...

Prasanna Padmanabham 4I

So basically, when drawing Lewis Structures, the first goal should be to get the smallest formal charge for all the atoms. Does this mean that I should give double bonds to structures even if it means breaking the octet rule if it means that all the atoms in the molecule will have a formal charge of...

Prasanna Padmanabham 4I

For the midterm, do you think we need to know how ions are named? For example in HW problem 2C.3, they gave the name of the ion/molecule (instead of the molecular formula) and asked us to draw a Lewis structure. Do you think that's how the midterm is going to be or do you know if we will get a molec...

Prasanna Padmanabham 4I

Dipole moment exists for any covalently bonded molecules where the atoms have different electronegativities. This is because one atom will exert a stronger force on the electrons and "hog" the electrons from the less electronegative atom. Therefore, the dipole moment exists when there is a...

Prasanna Padmanabham 4I

You should watch this video by Bozeman Science: https://www.youtube.com/watch?v=2AFPfg0Como. The first 7 minutes are an intro to what the different subshells and energy levels are, but he talks about writing electron configurations at the 7-minute mark.

Prasanna Padmanabham 4I

So there is a progressive scale of bonds that ranges from ionic to covalent. For example, if two atoms with really different electron affinities share "electrons" sometimes, electrons might hang out with the atom with more electron affinity (like the Oxygen side of H2O being a bit more neg...

Prasanna Padmanabham 4I

Hello, I have a question about what subshells "l" numbers are. For example if n=3, then l = 0, 1, 2 or basically l = 0,1,2...n-1. Then if n = 5, then l = 0,1,2,3,4 right? So if an "l" value of 0 corresponds to the "s" subshell, 1 corresponds to the "p" subshel...

Prasanna Padmanabham 4I

The standard unit used for kinetic energy is "Joules." For ionization energy, it is measured in Kilo Joules/mole or ElectroVolts. The units are all measuring the same thing, but the scale is different. For example, you can use inches, millimeters or even miles to measure different lengths,...

Prasanna Padmanabham 4I

I'm pretty sure you usually just have to draw like one of the structures (unless specifically asked to draw all).

Prasanna Padmanabham 4I

I'm not sure what exactly you are asking clarification for, but the reason why we use the octet rule is that it usually works for the elements in the first two columns and the last six columns (well noble gases don't really react with anything because they have full octet) of the periodic table. Thr...

Prasanna Padmanabham 4I

That's a really interesting question. I think it is because that Hydrogen is a really simple atom with one proton and one electron (which makes examples easier), but I'm curious to hear what other people have to say.

Prasanna Padmanabham 4I

For a list of atoms with different electron configurations check this website out: [url]https://www.scribd.com/doc/13771509/Electron-Configurations-of-Elements-Which-Are-Exceptions-to-the-Rule
[/url]

Prasanna Padmanabham 4I

anions are ions that are negatively charged (have more electrons than normal), and cations are those that are positively charged (have less electrons than normal).

Prasanna Padmanabham 4I

Will do, Thank you!

Prasanna Padmanabham 4I

Hello, I am having trouble understanding the Schrodinger equation and lesson 1C in general, do you all have any videos or articles you recommend?

Prasanna Padmanabham 4I

This video is really informative (and animations are cute). https://www.youtube.com/watch?v=cd2Ua9dKEl8, it goes over spin and the Stern and Gerlach experiment and why it is important.

Prasanna Padmanabham 4I

The signs don't really matter, the -/+ or the "up" and "down" For the subshells, you can only have like a 1/2 or a -1/2 or up and down but you can't really have like two positive spins electrons in the same subshell or two negative spins electrons in the same subshell -- they nee...

Prasanna Padmanabham 4I

That a really good question and I'm looking forward to an answer too

Prasanna Padmanabham 4I

I agree with everyone here. I am not a auditory learner, so I forget concepts when I just listen to someone explain it. I find it extremely helpful to read the textbook and do every single example problem . This is really helpful because when I'm doing HW problems, I like to classify the problem and...

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