CHEMISTRY COMMUNITY

Diana Chavez-Carrillo 2L

Are we turning in our homework for week 10 to you through email?

Diana Chavez-Carrillo 2L

Could someone please explain to me why the slowest step is favored rather than the fast step?

Diana Chavez-Carrillo 2L

In Professor Lavelle's email, he mentions that we can use Chemistry Community up to the day of the final so I was wondering the same thing if there are only certain resources we can use. I do believe that since it is open book then we should be able to use our class notes.

Diana Chavez-Carrillo 2L

Does anyone know when or how we can get our Test 2 back from our TAs?

Diana Chavez-Carrillo 2L

I have never done a take-home final so I am wondering is there a time limit to do the final or is there just a deadline to submit by?

Diana Chavez-Carrillo 2L

Because many of the review sessions had to be canceled, what else are you guys doing to study? Since its open book, I am organizing my notes and going over concepts that I had a hard time understanding. I am also reviewing my tests and midterm and redoing problems to make sure I remember how to do ...

Diana Chavez-Carrillo 2L

Does anyone know when we will be given our take-home final? Is it still going to be on Sunday?

Diana Chavez-Carrillo 2L

Professor Lavelle was not specific about the structure of the final exam but he said that as soon as he sends out the link for the take-home final that there will also be instructions attached to it. He also said that the final would be straightforward so I hope that the questions may not be as comp...

Diana Chavez-Carrillo 2L

The integrated rate law tells us how much reactant concentration changes over time. The differential rate law tells us the rate as a function of concentration. In other words, it is the overall reaction as a function of reactant concentration. The differential rate law can help us figure out the int...

Diana Chavez-Carrillo 2L

1 Volt = 1 J/C so the units cancel out when you multiply; substituting the units in for -nFE, you get -(mol)x(C/mol)x(V=J/C), and you’re left with J for G Does n have units? I have seen some TAs and UAs write mole of e- when plugging in the numbers into n in that equation. But I have also heard tha...

Diana Chavez-Carrillo 2L

Our Test 2 grades will most likely be given to us next week (week 10) in our own discussions because I saw my TA grading them during the discussion so I am sure they will be ready by next week. Some TAs might even put the grades on MYUCLA before handing them back so you can always keep a lookout for...

Diana Chavez-Carrillo 2L

When you are given a problem sometimes they may give you a rate constant to solve for something else like concentration. For example, a given rate constant can be written with the following units: L/mol*s. This is the same as 1/M*s because M=mol/L so if we have L/mol then this is the inverse of mol/...

Diana Chavez-Carrillo 2L

Yes, the half-life and integrated rate law equations are on the constant sheet but I think that you will need to know which one goes with what order and how to use them.

Diana Chavez-Carrillo 2L

I believe it will only cover topics from the midterm up until the end of kinetics. Would it be up until the end of kinetics or the end of electrochemistry? Based on what Prof. Lavelle said it will only be from the 2nd part of Thermodynamics dealing with Gibbs and then all of the Electrochemistry (2...

Diana Chavez-Carrillo 2L

One of the UAs mentioned how we should not always rely on the anode to be on the left side and the cathode on the right side because it is possible for them to be switched. It would be more important for you to look at the given reaction and determine from there whether its a reduction (anode) or ox...

Diana Chavez-Carrillo 2L

First order is when the rate in a reaction is proportional to the first power of the molar concentrations of the reactants. Second order is a reaction that has a rate that is proportional to the square of the molar concentrations of a reactant. You can tell which order to use if they directly say wh...

Diana Chavez-Carrillo 2L

This was confusing to me at first as well but one of my UA's mentioned that we can just remember that the agents are opposite of what they do so if its oxidation then it will a reduction agent but if it's reducing then it will be the oxidizing agent. But it is still important to understand it concep...

Diana Chavez-Carrillo 2L

DesireBrown1J wrote:Does Lyndon have a practice worksheet for Test 2?

I do not think that he has a practice worksheet for Test 2 like the ones he makes for the midterm or final but you can always ask him questions about concepts you're confused about.

Diana Chavez-Carrillo 2L

I understand that a negative Delta G means that the reaction/process is spontaneous and thus favored but in today's lecture, Lavelle went over the equation: Delta G = -nFE and mentioned that we want and favor a very large negative Delta G so my question is what exactly constitutes a "very large...

Diana Chavez-Carrillo 2L

In today's lecture, Lavelle mentioned how we tend to use an inert conductor as an electrode to transfer electrons. He said to use Platinum but is it possible to use another metal or is it only Pt? How will we know when we need to use Pt?

Diana Chavez-Carrillo 2L

The salt bridge connects the ion solutions of the anode(oxidation) and the cathode(reduction). Essentially, the salt bridge prevents the build-up of charges by balancing the charges in the two ion solutions.

Diana Chavez-Carrillo 2L

Does anyone know when is the last day to get your midterm regraded?

Diana Chavez-Carrillo 2L

Lavelle mentioned in class that Test 2 will only be on the other part of Thermodynamics (I believe it is on the second page of Outline 4: Thermodynamics covering 5G.3, 5G.4, 5J.3) and Outline 5: Electrochemistry and its Applications. In his email, he mentioned that "Week 8 we start Kinetics but...

Diana Chavez-Carrillo 2L

Solid, liquid, gas...they all MATTER!

Diana Chavez-Carrillo 2L

Haha :)

Diana Chavez-Carrillo 2L

Dina 2k wrote:how soon does he usually have it graded and back to us?

My TA said that midterms will be graded and handed back to us after lecture on Wed.

Diana Chavez-Carrillo 2L

If you made more than 5 posts on one week then can the extra posts you made that week count for next weeks or do you have to make a minimum of 5 posts each week even if you made more than 5 on previous weeks?

Diana Chavez-Carrillo 2L

Professor Lavelle did not curve for Chem 14A so I'm sure he will follow the same grading system for Chem14B. On his syllabus, he mentions that he does not curve the grades so you have to make sure to get at least 50% of the total points (500 total points) in order to pass his class with a C- or bett...

Diana Chavez-Carrillo 2L

Gibbs Free Energy ( ∆G ) is the energy of a system that is free to do work at a constant temperature and pressure. Gibbs free energy is a state function and an extensive property. It gives us information about the spontaneity of a reaction. Spontaneity is when a reaction is naturally occurring. The ...

Diana Chavez-Carrillo 2L

I believe that it has the same relationship as Hess's law because they are both state functions (entropy and enthalpy), but they are not exactly the same because Hess's law only applies to enthalpy. There is a very similar relationship, but they are different because we cannot track H alone. It is ...

Diana Chavez-Carrillo 2L

You need a 50% to pass the class with a C-. The other letter grades are determined by the class average. Do you need a 50% in each assignment category to pass the class with a C-? Or a 50% in general. My TA made it sound like it was the former, which is kind of worrisome since I did so bad on the f...

Diana Chavez-Carrillo 2L

Since Hess's Law can be used for both enthalpy and entropy since they are both state functions and extensive properties, why is there no delta on the S for entropy as shown by its equation: ∆S°rxn = ∑ S° products - ∑ S° reactants but there is one for enthalpy: ∆H°rxn = ∑ ∆H° f products - ∑ ∆H° f rea...

Diana Chavez-Carrillo 2L

Why does it take more energy to vaporize (liquid to gas) than to melt/fusion (solid to liquid)? Does it have to do with their intermolecular forces?

Diana Chavez-Carrillo 2L

Robert Tran 1B wrote:A microstate is a possible arrangement of molecules in a given space. If there are more degenerate microstates, meaning that they all have the same energy, then the entropy is higher.

Why would having degeneracy or equal energy make entropy increase?

Diana Chavez-Carrillo 2L

In today's lecture, Professor Lavelle showed us the equation for the entropy of a system and surrounding as delta s = q / T. He mentioned how there was some sort of inverse relationship between the q and T which determine if entropy is increasing or decreasing. I am a visual learner so it was a bit ...

Diana Chavez-Carrillo 2L

Irreversible and Reversible changes can occur with isothermal expansion meaning the temperature is constant or ∆T = 0. In irreversible you use the equation: w= -Pe * ∆V which is usually used when you are given constant pressure. For reversible you use the equation: w= -nRT * ln (Vf / Vi). A reversib...

Diana Chavez-Carrillo 2L

Today in lecture Lavelled mentioned how an exothermic reaction has lower enthalpy is it because heat is being released to products? Also, I was confused about how products had lower energy so it was spontaneous? What does he mean by spontaneous?
Thank you!

Diana Chavez-Carrillo 2L

You can find these math resources on his chemistry website under the section "Math Assistance." He said that we should read over the "Integration Rules with Applications in Chemistry" and "Common Antiderivatives with Applications in Chemistry." These two go over the con...

Diana Chavez-Carrillo 2L

Does anyone know what the average was for scores on Test 1? Also, could someone explain to me how they did problem #5? I did the ice table and plugged in the products over reactants for Kb and then I tried to solve for Kb but I think I got confused with the next steps.

Diana Chavez-Carrillo 2L

I had the same question because I was curious about what the correct answers were. I think that it would be a good idea to ask Lavelle because there was an answer key for the midterm so I hope that there is one for the final as well. You should email Lavelle or talk to him after the lecture. Also, y...

Diana Chavez-Carrillo 2L

Solids and liquids like water are not included in the equilibrium calculation. Only gas or aqueous in the reaction are counted for. This is the same rule that applies when using the ICE tables and even with Le Chatelier's Principle because changes in the concentration of a liquid or a solid DO NOT a...

Diana Chavez-Carrillo 2L

Kw= 10^-14 and Kw= 1.0 * 10 ^-14 are the same but I believe in the book they used 1.0 * 10 ^-14 because it helps keeping up with the sig figs. But remember that Kw=10 ^-14 ONLY at 25 degrees Celsius.

Diana Chavez-Carrillo 2L

Would this be the same for going up a phase? Would it be endothermic in this case since now there is more heat required to break down the phase like a solid to liquid?

Diana Chavez-Carrillo 2L

Usually in the problem will you be given molarity or moles and this will hint that you need to use concentration (Kc) but if the problem gives you atm or barr then you will use the partial pressure (Kp). However, the question should be clear about which one you should be using from the given informa...

Diana Chavez-Carrillo 2L

In an endothermic reaction, heat is being absorbed so you can think of it as a reactant. In an exothermic reaction, heat is being released so you can think of it as a product. You can usually tell whether a reaction is endothermic or exothermic by looking at the given enthalpy. If the enthalpy is a ...

Diana Chavez-Carrillo 2L

In today's lecture Lavelle mentioned something about a Buffer, can someone explain this concept for me and how it relates to the pH of a weak acid/base and salt?

Diana Chavez-Carrillo 2L

The reaction quotient (Q) formula looks very similar to the formula used for the equilibrium constant, K so what is their difference? Is it just that K has to be at equilibrium or is there other differences between them?

Diana Chavez-Carrillo 2L

I like to read the textbook chapters because they definitely do break down the topics and also I like to use Khan Academy to study for the tests. You can search up chemical equilibrium or acids and bases on khan academy and the lesson plans for them will pop up. I like using this resource because th...

Diana Chavez-Carrillo 2L

I went today to the room in Young Hall and they said finals will for sure be available next week (week 3). I am also wondering whether the rationale for the final exam questions will be provided to us either online or with our physical exam? Also, in case there are some errors with the grading of ou...

Diana Chavez-Carrillo 2L

Is it possible for there to be an equation with both gaseous particles and aqueous solutions? How would we go about solving this? Would we use a combination of Kc and Kp?

Diana Chavez-Carrillo 2L

I was wondering the same thing and I checked my email because I remember Lavelle mentioned final exam pickups somewhere. He sent an email about the class average grades and at the bottom, he said: "Final exams will be available 3rd week Winter quarter from 3034 Young Hall." So I am going t...

Diana Chavez-Carrillo 2L

For the homework problem 5H.1 part B it contains fractions as the stoichiometric coefficient: 1/2 N2 + 3/2 H2 -> NH3. In the solution manual they placed 41 (this number is K=41 which came from part A) to the power of 1/2 and got 6.4 as the value of K for this equation but I am confused about where y...

Diana Chavez-Carrillo 2L

They essentially mean the same thing, and another one you might see is that it "favors" one side. Okay, I see thank you! However, for the "favors" part I remember seeing in his module (the first module I believe) where K>1 means that there is a "slight" favoring of pro...

Diana Chavez-Carrillo 2L

I know Professor Lavelle kept emphasizing how elements can't literally sit or lie anywhere but I was confused on their differences because I see that they can be used interchangeably so do they all mean the same thing? For example, if K>1 then would we say it shifted, lies, or sits to the right?

Diana Chavez-Carrillo 2L

Professor Lavelle announced in class that homework 1 will be turned in after the lecture on Friday (tomorrow 01/10). However, this is only for week 1 so for week 2 and the following weeks the homework (5 problems) will be turned in to your TAs when you have your discussion sections.

Diana Chavez-Carrillo 2L

To go off of the previous responses, although units are omitted when we write K we write a C or P next to it which indicates the units we are using without necessarily writing them. The purpose of this is to make sure that it is clear whether we are calculating concentration or pressure. For Kc, it ...

Diana Chavez-Carrillo 2L

In the first module Lavelle mentioned how K>1 means that there is slight favoring of products and K<1 measn there is slight favoring of reactants. Are K< or > 1 and K< or > 10^3 or 10^-3 not the same and why? I remember in lecture Lavelle mentioning how for K< or > 10^3 or 10^-3 you either favor the...

Diana Chavez-Carrillo 2L

Did you buy the bundle or the book separately because I had bought the bundle and it came with a solution Manual book? The solution manual is an orange book but if you do not have it then I believe you can also find the answers to the homework questions on the back of the textbook.

Diana Chavez-Carrillo 2L

this is unrelated but can someone help me please? I can't figure out how to post something without replying to someone... The way that I have done it is with the following steps: 1. On the top left-hand corner, you should see the word/link "Board Index" (click it) 2. Scroll down to the Ch...

Diana Chavez-Carrillo 2L

I remember that some students from 14A mentioned how there were practice questions on Sapling Learning and Lavelle emphasized that students should do them. Anyone who has used the Sapling Learning for 14A was the questions similar to the exam questions and would they be helpful for 14B?

Diana Chavez-Carrillo 2L

I was confused as well as to why the solution manual did not write Kp and just wrote K. However, on the solution manual the ratio was written with "P" in front of each reactant or product which indicates that the ratio is the equilibrium of their partial pressures. Based on Lavelle's modul...

Diana Chavez-Carrillo 2L

Reina Robles 1H wrote:You use those when the ligand already contains a prefix (for example, (en)), is a polydentate, or it starts with a vowel.

I hope this helps!

Just to clarify, we only use prefixes for whats inside the brackets and not on the cation or anion outside the brackets correct?

Diana Chavez-Carrillo 2L

For sure know ethylenediamine (en), oxalato (ox), and ethylenediaminetetraacetato (edta) because they are chelating ligands!

Diana Chavez-Carrillo 2L

Will the test focus more on the first or second half of the class? The exam will be cumulative so expect to apply concepts together because many of the concepts we learned in the first half of the class apply to the second half such as molarity and calculating pH. So I am pretty sure there will be ...

Diana Chavez-Carrillo 2L

Hello, I have a question about the difference between 2sp3 and sp3. How do you know if the "2" in front of the sp3 is supposed to be there? What's the difference between the two? It’s the quantum number of the central atom when you’re talking about the hybridization of a molecule. Describ...

Diana Chavez-Carrillo 2L

#16 why is the trigonal planar shape considered nonpolar, how did we determine this ? AX3 means that the central atom (A) will have 3 atoms attached to it (X3). This results in a trigonal planar shape. To determine its polarity usually if the attached atoms are all the same type of atom and the cen...

Diana Chavez-Carrillo 2L

In the marshmallow packet, for question 28, for example, would it be acceptable to write (en) instead of the full name: ethylenediammine or do we need to write out the full name to get credit?

Diana Chavez-Carrillo 2L

for question 40c, how do you know whether o2 or o3 has the stronger bond and why? o2 has double bonds that are shorter and therefore stronger than the o3 bonds, which is between a single and double bond due to resonance. So then is the stronger bond O2 because in a way O3 has like an average bond s...

Diana Chavez-Carrillo 2L

When asked what the hybridization is when do we have to write, for example, 2sp3 or just sp3?

Diana Chavez-Carrillo 2L

When do you use the suffix ide or ate? When you are dealing with a molecule that is NOT a ligand and is an ANION and outside of the brackets then you add the suffix -ide because it does not follow the ligand rules. For an anionic (negative charge) metal (inside the bracket), you add the suffix -ate.

Diana Chavez-Carrillo 2L

Are you talking about ammine for the neutral lignad: NH3 and about their spelling? If so, I was told in one of my plf's that the spelling matters in regards to points so when naming coordination compounds make sure you write ammine with double m's!

Diana Chavez-Carrillo 2L

I would say to definitely do the homework problems and review them because they give you a good idea of how the questions for the test can be structured. Also, I would say it would be a good idea to read over your notes and attend UA's sessions since they sometimes provide and go over practice probl...

Diana Chavez-Carrillo 2L

AngieGarcia_4F wrote:If you were given a Hydrogen concentration of [H+]=0.1M, for example, and asked to find the pH, you would plug the concentration into the formula pH=-log[H+]; pH=-log[0.1M], and just plug it into your calculator.

So would our answer just be 1? Also, would this be interpreted as our pH being 1?

Diana Chavez-Carrillo 2L

Based on the type of questions that were given to us from some of the UAs the questions are phrased by saying "refer to the LOWEST ENERGY structure of..." or "refer to the MOST STABLE Lewis structure of..." So I am sure that the majority of the time we will be asked to draw and u...

Diana Chavez-Carrillo 2L

I believe we will have to memorize all the shapes because in Test 2 we will be tested on drawing the Lewis structures, determining the shapes, bond angles, etc. as we have done with the practice problems in lecture with Lavelle.

Diana Chavez-Carrillo 2L

Yes if asked for one bond angle then you can either say it is slightly less than 90 degrees or slightly less than 120 degrees. The reason for this is because the one lone pair causes electron repulsion than push the atoms closer together because the atoms want to minimize the electron repulsion expe...

Diana Chavez-Carrillo 2L

VSEPR Table.pdf Really? Do you know where I can find his post?? [/quote] Wow! Thank you so much this helps a lot! Quick question about the chart so in domain 6 is the angle for AX5E less than 90 degrees? And is the reason why the bond angles in AX4E2 still 90 degrees because of the two lone pairs i...

Diana Chavez-Carrillo 2L

alicechien_1I wrote:I believe we only need to know up to octahedral. Dr. Lavelle made a post with the list of molecular geometries to know for the test. Hope this helps!

Really? Do you know where I can find his post??

Diana Chavez-Carrillo 2L

Up to what steric number (region of electron density) should we know/memorize for VSEPR? I know that it can go up to steric number 7 for example which the shape would be called pentagonal bipyramidal.

Diana Chavez-Carrillo 2L

Induced dipole - induced dipole is the same as London's dispersion right? I keep hearing people refer to this intermolecular force as either induced dipole - induced dipole or London's dispersion so I just want to make sure if they mean the same thing?

Diana Chavez-Carrillo 2L

So the number of lone pairs can also determine the molecular shape of a molecule? Yes, lone pairs can influence the molecular shape of a molecule but as mentioned by the previous responses we have not gone over it yet. However, to have an idea of some examples I provided an image below that shows y...

Diana Chavez-Carrillo 2L

I believe Test 2 should be what was not covered on the midterm and the next chapter with Molecular Shape and Structure. This includes 3F which was what we did not cover from the midterm and Outline 4: Molecular Shape and Structure.

Diana Chavez-Carrillo 2L

I feel like definitely VESPR models like the practice we did today in class drawing the lewis structure, calculating the angles and determining the shape would be on there. So I would say study 3F (since we did not cover it in the midterm) and 2E-F.

Diana Chavez-Carrillo 2L

So the number of lone pairs can also determine the molecular shape of a molecule? Yes, lone pairs can influence the molecular shape of a molecule but as mentioned by the previous responses we have not gone over it yet. However, to have an idea of some examples I provided an image below that shows y...

Diana Chavez-Carrillo 2L

Yes, my TA said we can do HW problems from chemical bonds and/or molecular shape and structure since we did not cover all of the chemical bonds and Lavelle finished covering it after the midterm. But I would suggest you try to do more HW problems on the section with molecular shape and structure sin...

Diana Chavez-Carrillo 2L

Polarizability is the ability of an atom to form temporary dipoles. In other words, it is the ability to be polarized by another. Polarizing power is the ability to polarize another. Typically a bigger atomic radius means higher polarizability because a bigger electron cloud is more easily distorted...

Diana Chavez-Carrillo 2L

So far what I have gathered from TAs and Lavelle's lectures, the exceptions include the following: Incomplete octets (meaning it can have less than 8 electrons) are the first 4 elements on the periodic table: H, He, Li, Be, AND B, Al. Expanded octets (meaning it can have more than 8 electrons) are e...

Diana Chavez-Carrillo 2L

Just keep in mind that the ionzation energy trend is not exactly the same as the electronegativity trend because for ionization energy there is an exception when it comes to Nitrogen and Oxygen. For the most part, ionization energy does increase going up and across to the right of the periodic table...

Diana Chavez-Carrillo 2L

So then when it comes to ionization energy is the only exemptions nitrogen and oxygen? Are the rest of the elements still increasing in ionization energy going up and across to the right of the periodic table which is the same trend as electronegativity on the periodic table?

Diana Chavez-Carrillo 2L

Does anyone know if we can use whiteout during the midterm exam? I know we are supposed to write in pen so I was wondering if we could use whiteout since we do have a limited amount of space to do calculations.

Diana Chavez-Carrillo 2L

Yes, electronegativity counts as a trend on the periodic table. It is important for things like determining if elements have an ionic bond or a covalent bond. Electronegativity, electron affinity, and ionization energy have the same trend (increase up the table and to the right across the periodic t...

Diana Chavez-Carrillo 2L

Since we need to know the electronegativity differences to determine if there are ionic bonds or covalent bonds, will we be given on the midterm an electronegativity chart that shows each element's electronegativity or do we need to memorize them?

Diana Chavez-Carrillo 2L

Will we be given some sort of answer key or rationale for the correct answers in Test 1 in order to review our mistakes and thus study for the midterm that will include questions similar to Test 1?

Diana Chavez-Carrillo 2L

In today's lecture (10/30/19) Lavelle mentioned how Cl has a (-) charge while K is (+) charge. I know its probably really simple but could someone please clarify/remind me how do we determine if an element is +1 or -1. For example, how is Cl becoming into Cl-1 and K becoming K+.

Diana Chavez-Carrillo 2L

Would we still be given partial credit for questions on the midterm like Test 1 or no?

Diana Chavez-Carrillo 2L

Is electron affinity only important/ only affects Group 17 (according to Lavelle) and noble gases? Or why is it important to know the electron affinity?

Diana Chavez-Carrillo 2L

I think some of the main trends you should keep in mind are: Electron affinity: Lavelle mentioned that this is less periodic but generally there is HIGH electron affinity for elements in the TOP RIGHT of the periodic table (Group 17). Atomic radius : increases DOWN the periodic table increases FROM ...

Diana Chavez-Carrillo 2L

What does the infinity-like symbol next to the equation (q1)(q2)/r mean?
Also, would we need this equation to do calculations or is it just the concept about like attraction and potential energy that we need to understand?

Diana Chavez-Carrillo 2L

Does anyone know if any other UAs post their worksheets on Chemistry Community?? These worksheets are so helpful especially for me whose high school chemistry background is essentially nonexistent. Thank you so much Karen for posting these! Yeah, I found another UA who posts helpful worksheets too ...

Diana Chavez-Carrillo 2L

Could someone explain to me why is it that when you start to include the d into our electron configuration the order is that d goes first then s. In highschool I was taught to just follow the order where it is s then p for the first 3 rows but then for the 4th row it would be s, d, p but I see that ...

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