CHEMISTRY COMMUNITY

Abril Guanes 2A

There has been conversation in multiple review sessions about whether E/E0 are state functions. Some people are saying that are for redox reactions so you can add E0 values together, but if the reaction is not a redox then you have not to convert E0 to deltaG0, add those to values together and then ...

Abril Guanes 2A

What are the units for activation energy?

Abril Guanes 2A

Hey guys.
I was wondering if anybody who went to Matthew's workshop could explain how they found the rate law and the value of the rate constant. Thanks :)

Abril Guanes 2A

Hey everyone! I'm a little bit confused about the wording around some of these terms. I just wanted some confirmation. Reducing Agent: Does the reducing so is being oxidized by giving up electrons Oxidizing Agent: Does the oxidizing so is being reduced and readily accepts electrons Reducing Metal: ?...

Abril Guanes 2A

Hey guys, I was wondering how you guys went about solving these questions. I'm having a hard time reading the diagrams and understanding how to derive the half reactions from them. Also, the answer question was mentioning flipping reactions for anodes, and I don't really understand that part either....

Abril Guanes 2A

UPDATE: it's working now!

Abril Guanes 2A

Hi everyone! I'm currently trying to do the week 9/10 homework but it's not loading. There's an error message about network problems and stuff. I was able to log in originally and do like the first 3 problems but when I clicked to go to the next one, it pooped out and said something about network er...

Abril Guanes 2A

I just wanted to confirm that the cathode is always on the right side of a diagram. I believe in the textbook it said that if the cell potential is negative, that the cathode is on the left. Can someone please confirm this detail? :) Thanks!

Abril Guanes 2A

I am a little bit confused about how to use the graphs. Are we ever going to have to graph the rate plots or will they be given to us? Also, if we are suppose to graph them ourselves, is kind of like trial and error. So for example, you graph ln[A] vs time and it does NOT give you a straight line, t...

Abril Guanes 2A

Hey all, I feel like I missed a massive chunk of the kinetic sections when it comes to order. I had a previous post about what order it. If a reaction has 1 reactant, that makes it a first-order? If it has two does that make it a second-order? How do we determine if a reaction is dependent upon 1 re...

Abril Guanes 2A

Can someone PLEASE explain what is meant by "order" in this unit. What is meant by first-order, second-order, etc? Thank you :)

Abril Guanes 2A

Can someone PLEASE explain what is meant by "order" in this unit. What is meant by first-order, second-order, etc? Thank you :)

Abril Guanes 2A

In sapling question 1, the solution says that K in both KClO4 and KCl is a monoatomic ion, but Cl is only a monoatomic ion in KCl and not in KClO4. I was wondering why that is?

Abril Guanes 2A

In the Applications lecture, Lavelle went over this example of 0.1M of Ag+ being in 0.1M NO3 - separated by a porous disc with 1M Ag+ in 1M of NO3-. He had mentioned that the concentration of Ag one the 0.1M side would begin to increase but I was wondering how that would be. Is the porous disc open ...

Abril Guanes 2A

The shorthand is done based on what comes in contact with what first. So for this one, the shorthand is Pb l PbCl2 l Cl- ll Cl- l AgCl l Ag. The anode is on the left and the cathode is on the right.

Abril Guanes 2A

Can someone explain why the S.H.E has an Enaught value of 0, please? Thanks!

Abril Guanes 2A

Hey everyone!
I've seen this problem a lot on Chemistry Community and I've followed everyone's instructions and I'm still getting the wrong answer. I'm on my 11th attempt, so if anyone can tell me what's up, I would very much appreciate it!

Abril Guanes 2A

Hello! This question was kinda tricky. To begin, you use the enthalpies of formation to get the total enthalpy for the reaction. Then you have to take 1/4 of that to find the enthalpy for the TNT, which is done because there is 4 moles. This is the amount of energy released by the reaction as the TN...

Abril Guanes 2A

Stability is based on Gibbs free energy and not just entropy. For example, lets use the reaction A --> B + C. If the Gibbs free energy is negative, A is not stable: When Gibbs free energy is negative, the reaction is spontaneous. Therefore, A will turn into B and C without the help of an outside fo...

Abril Guanes 2A

Higher entropy means higher disorder and more possible arrangements. The entropy of gases > the entropy of liquids > the entropy of solids. However, when looking at whether a molecule is likely to form, we also need to take into account enthalpy and the temperature of the reaction to see if the for...

Abril Guanes 2A

This is more of a confirmation question that I deduced while doing the textbook problems.

A more negative entropy means more disorder, which suggests less stability.
A more positive entropy means more order, which suggests more stability.

Please correct me if I'm wrong :). Thanks!

Abril Guanes 2A

Hey everybody! I have a question about two types of problems. Question 4J.5 gives this problem and how I tend to solve this problem is to write a balanced equation and solve from there. However, the solution manual seems to have fractional coefficient and calculates the delta H/S per 1 mole when the...

Abril Guanes 2A

Question: Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The conta...

Abril Guanes 2A

Hey! I also have a part-time job. I work for UCLA IT Support Center and I work about 12 hours a week. The most important thing is to give yourself time to relax and decompress, especially with a class like Chem that is really stressful. I've started going on walks with my roommate and weekend hikes ...

Abril Guanes 2A

Hey all! I was doing the homework yesterday and came across this problem. I was wondering if there were any situations that would fit into the middle two boxes. Thanks!

Abril Guanes 2A

Hello! First step is determining the right equation. The only thing that is mentioned here really is the volume change so the right equation would be delta S = nRlnV2/V1. You're indirectly given the moles as 1 and you know the R constant. For problems like these, I would recommend assigning random v...

Abril Guanes 2A

In class, we did that example of Br2 (l) --> Br2 (g). Part of the explanation said that when T > 333K that the delta S dominates but when T < 333K that delta H dominates. I was wondering if someone could explains what it means for these two terms to dominate? Thanks!

Abril Guanes 2A

This may be a dumb question, but what exactly does G represent? I know that, for example, q is heat and H is enthalpy, but I'm not sure how to summarize G inn a similar fashion. Thank you! :)

Abril Guanes 2A

In class today, Dr. Lavelle mentioned that at thermo equilibrium there is no transfer of heat. I was wondering if this means no NET transfer of heat, but rather just an equal movement of heat (kinda like in chemical equilibrium, or no transfers of heat at all. Thanks!

Abril Guanes 2A

Hello! Can someone explain what it means for a system to be at thermo equilibrium please? How can you tell if a system is at thermo equilibrium? Thank you!

Abril Guanes 2A

Hello! Something I find really helpful is really just going through the textbook and assigned readings. The textbook really breaks down the different equations, which is something I struggle with. Going through the example boxes and making sure you understand everything that is being done is super h...

Abril Guanes 2A

Hey guys!
I was wondering if anybody knows or is a part of any cool clubs? I'm looking for some ways to keep busy for the time being. Feel free to drop any kind of club, thanks! :D

Abril Guanes 2A

Based on the diagram he had at the beginning of the lecture, it looks like the heat comes from the surrounding. So the surroundings serve as a heat reservoir.

Abril Guanes 2A

Hello! I think your setup would look a little something like this. Using the q = mCsdeltaT equation you can input the information that you know from both the ice cube and the water and set them equal to each other. (53.0g)(4.184 J/g*C)(Tf - 0C) = - (444g)(4.184 J/g*C)(Tf - 45C) You then multiple the...

Abril Guanes 2A

In Monday's lecture, it was said that reactions at constant pressure that involve solids and liquids, the PdeltaV is insignificant, so deltaU = to enthalpy. Can someone explain why that is? Why is PdeltaV insignificant in this circumstance? Thanks!

Abril Guanes 2A

This chemical equation is an example of the enthalpy of combustion of CH4. You know this because CH4 is reacting with water to form CO2 and H2O, which are standard productions of a combustion reaction. Does that answer your question? I hope it does!

Abril Guanes 2A

The midterm covers up to the Friday lecture on the 22nd.

Abril Guanes 2A

I'm pretty sure the equilibrium constant K does not have units, but for pressure the units are either barr or atm.

Abril Guanes 2A

I'm not sure but there were textbook problems about the deprotonation of acids like H2SO4 and others that have two protonations, meaning you would have to do two ice tables. I would know how to tackle these types of problems!

Abril Guanes 2A

I had the same question. When I was doing the textbook problems, I read that you ignore the second protonation when the Ka value of the second protonation is less than the first. So basically when KA2 < than KA1.

Abril Guanes 2A

I'm sure they will be provided, as the list is very long. My guess is that they will provide the resources on a problem-by-problem basis, meaning that for a midterm on the exam there will be a table with the information needed for that particular problem. Or we will be allowed to print out the table...

Abril Guanes 2A

Hello! I was wondering if there is a particular way to decide which method to use for solving enthalpies. Are there key words that we should look out for? Also, will we be allowed to print out the tables with all the bond enthalpies and all that good information for the exams or will we be given the...

Abril Guanes 2A

I heard from people in a UA session that today, Friday, is the last lecture that covers content in Midterm I. So there's a little bit of thermodynamics on the midterm, in addition to Acids and Bases and Chemical Equilibrium.

Abril Guanes 2A

This is a long one boys! In a textbook problem 5.61 it gives the photosynthesis reaction 6 CO2 (g) + 6H2O (l) ---> C6H12O6 (aq) + 6O2 (g). For this problem, it asked what affect the addition of water would have on the overall reaction, to which I said it would have no effect because water is already...

Abril Guanes 2A

Hello! I was doing this textbook problem and had a question. When finding the Kc value for the reaction at 298K, the table says 6.1x10^23. Because the table gives the reaction for N2O4 -> 2NO2, I realized to do 1/(6.1x10^23); however the textbook goes the inverse of (6.1x10^-3) and was wondering if ...

Abril Guanes 2A

Hello!
Last quarter we learned that if the pH < pKA then it'll be neutral predominant species and if the pH > pKA then there will be a charged predominant species. This may not make sense, but can someone explain this same concept in terms of pOH and pKB. I struggle a lot with bases :/. Thanks!

Abril Guanes 2A

Hello! I wanted to confirm how to approach all types of these questions? When we first started doing these kinds of problems, I struggled with deciding if I should write the equilibrium starting with NH3 in water or NH4Cl in water. Is it safe to assume that we should write the equilibrium for the ac...

Abril Guanes 2A

Hello!
I had a clarifying question. It's my understanding that high KA values and lower pKA values indicate a stronger acid. I was wondering if someone could explain that same concept for bases. Does a higher KB and lower pKB suggest a stronger base? Thanks!

Abril Guanes 2A

Hello!
This was discussed in 14A, but I need a refresher. I was wondering if someone could explain how they get to that answer (bottom right corner). Thanks!

Abril Guanes 2A

Hello! In lecture, Lavelle said that stronger acids have weak conjugate bases and stronger bases have weak conjugate acids. I was wondering if this is true for the inverse, so if there is a weak acid, is the conjugate base stronger? And if so, they are not considered strong bases like the hydroxides...

Abril Guanes 2A

I would also like to add that when setting up the equation after the ICE table, to set it equal to 1/Kc, since you are now using the reverse reaction. I think this applies for number 10 as well!

Abril Guanes 2A

This may be a non-brainer for some people, but why are endothermic reactions favored? Or did I misunderstand what was said in lecture today? Thanks!

Abril Guanes 2A

Hello! There are a couple of places to look for the Honors Program! I found this website with information about the application and requirements, as well as an email that you can contact with any questions. I hope this helps! http://www.honors.ucla.edu/college-honors-program/joining-the-program/ (P....

Abril Guanes 2A

Hello!
This may be a very nuanced question, but I know intermediate values of K suggest that neither reactants or products are STRONGLY favored in the reaction. In these situations, are the products or reactants favored at all, even if weakly or is that not the case? Thanks!

Abril Guanes 2A

In lecture today, Dr. Lavelle said that most problems should specific whether they want Kc or Kp; however, none of the Module problems specified whether they wanted use to solve Kc or Kp. I understand that the problem will hint at whether it's Kc or Kp when giving partial pressure or concentration, ...

Abril Guanes 2A

Do we need to memorize the strong/weak acids and bases. For the most part I have em down, but I just want to make sure. Thanks Hey! I learned a way to memorize the strong acids from the UA sessions. Its as follows: "SO I BRought NO CLean CLOthes" SO refers to H2SO4, I refers to HI, BR ref...

Abril Guanes 2A

Diatomic molecules are molecules composed of two atoms that are the same. Some examples are H2, O2, N2, F2, I2, Cl2, Br2.

Abril Guanes 2A

Hello! I was taught this in a UA session last night. When the pH < pKa, it means the environment is acidic, so the molecule has no reason to give a proton and make the solution more acidic, so it will make the acid neutral. When the pH > the pKa, it means the environment is basic. If the environment...

Abril Guanes 2A

Hello! CO2 reacts with water to make carbonic acid , H2CO3. Carbonic acid is a strong acid, meaning it gives off H+ protons very readily. Carbonic acid will give off an H+ proton, making it HCO3-, which is bicarbonate, a weaker acid than carbonic acid. Once the carbonic acid has given off a proton, ...

Abril Guanes 2A

Hey! The best method is unfortunately memorization but the other day I found a pneumonic for remembering the strong acids. Its "SO I BRought NO CLean CLOthes" SO refers to H2SO4, I refers to HI, BR refers to HBR, NO refers to HNO3, CL refers to HCl, and CLO refers to HClO4/HClO3. I hope th...

Abril Guanes 2A

I am having an incredibly hard time identifying whether something is an acid or a base just by either 1) looking at it or 2) using methods that were talked about in class. I understand compounds with (OH) attached tend to be bases, but for example LiClO4 (Li being an ion just floating around and ClO...

Abril Guanes 2A

Hello! I understand that when writing the name, the ligands are in alphabetical order, but how about when writing the formula? For example (just making this up), [Co(OH)3(NH3)4]. In this case, ammine would go first, but what if we were given the name first and had to work backgrounds to write the fo...

Abril Guanes 2A

Usually the name would be smashed all together and usually the textbook and other people separate it with hyphens to make it more clear. I don't think either one is incorrect, but I would be comfortable with reading both. The long, smashed ones tend to be harder to read, but I would just be okay wit...

Abril Guanes 2A

I have yet to start the homework, but just by looking at your answer I worked backwards to get the formula. [Co(NH3)5Cl]Cl. The Cl inside and outside both have a -1 charge, and ammine has no charge. Adding the two -1 charges from the chlorine ions would make a -2 total charge, but since everything ...

Abril Guanes 2A

Hello!
The -2 on the outside means that the molecule has an overall charge of -2. Because you have 6 Chlorines, each with a -1 charge, that makes -6. Because the molecule has a -2 overall charge, you now know that Pt has an oxidation number of +4. I hope this makes sense!

Abril Guanes 2A

I have yet to start the homework, but just by looking at your answer I worked backwards to get the formula. [Co(NH3)5Cl]Cl. The Cl inside and outside both have a -1 charge, and ammine has no charge. Adding the two -1 charges from the chlorine ions would make a -2 total charge, but since everything i...

Abril Guanes 2A

Hello! We went over this today in Lavelle's office hours and he recommended drawing out the structures to see which have atoms with single bonds and lone pairs that could bond. If the ligand has more than one atom that has a single bond and a lone pair available to bond, then that ligand is polydent...

Abril Guanes 2A

Hello! I am a little rusty on the 7 series information, but I'm sure others can add to this. Essentially, we know that gases like to naturally move from higher partial pressure to lower partial pressure. In the pulmonary capillaries, the partial pressure of oxygen is very high, causing oxygen to bin...

Abril Guanes 2A

H2O would actually be bent shape because the two electron pairs from the oxygen will push the bonds between hydrogens down, giving it a bent shape.

Abril Guanes 2A

So polar/nonpolar bonds refer to the specific bonds within a molecule. Polar and nonpolar molecules refer to the overall molecule. So for example, H2O has polar bonds and is overall a polar molecule. On the other hand, CO2 also has polar bonds, but because the structure is linear and the dipoles can...

Abril Guanes 2A

Hello! I was having trouble how to find out if an orbital is unhybridized. In his Monday lecture, Professor Lavelle would point a some part of the molecule, explaining that it did not have a hybrid orbital, and I wanted to know how you can tell that when looking at a molecule? Thank you and happy ho...

Abril Guanes 2A

Hello! I had a question on Sapling HW #8. The question was: "Select the correct statement about the relative positions of the hydrogen atoms in the three structures. a. The hydrogen atoms of H2CCCH2 and H2CCCCH2 lie in the same plane. b. The hydrogen atoms of H2CCH2 and H2CCCCH2 lie in the same...

Abril Guanes 2A

I think he means to not schedule a class at the same time as the Chem 14B lecture, because although it is recorded, he plans to have exams like midterms held during lecture time rather than discussion times. I heard some students were asking if they could double-schedule Chem 14B with another class ...

Abril Guanes 2A

I'm not entirely sure, but I do know that the final is 1 hour and 30 minutes instead of a typical 3 hour final. If the midterm of 50 minutes was 12-16 questions, I would assume that it would be in the mid-20 to low 20s for the amount of questions. Hopefully he'll drop info on the final soon!

Abril Guanes 2A

Hello! BeCl2 has polar bonds but is non polar overall. Because Be does not have any lone pair electrons the shape will be linear, so the dipoles from the Cl will cancel out. H2O also has polar bonds because the oxygen will pull the electrons from the hydrogen. The shape of H2O is bent though because...

Abril Guanes 2A

First, you would want a negative charge on the most electronegative element in the molecule. Second, because carbon is the central atom, you do not want a charge on it (or any central atom for that matter) because it makes the molecule very unstable, making it unfavorable. Hope this helps!

Abril Guanes 2A

For this example you would have to think about the size of the electronegative atoms. Fluorine, although very electronegative, is relatively small compared to Iodine. Because iodine is much larger, it has more electrons and making it more polarizable. Because it is more polarizable and has more elec...

Abril Guanes 2A

Hello! Matthew doesn't post his answer key anywhere, he only gives out answers in the UA sessions. I'm not sure if you email him, he'll send you an answer key (as many UAs deal with past exam questions, they don't want those circulating). Regardless I found his email for you: mtran060@g.ucla.edu. I...

Abril Guanes 2A

Jaclyn Dang 3A wrote:Are lewis acids and bases going to be on this exam?

I saw it on the Outline 3 as a guideline. "Identify Lewis acids and bases", so I suppose so.

Abril Guanes 2A

Hello! Can someone help me by writing a general rulebook / guidelines for identifying Lewis acids and bases? I'm struggling with identifying them on the homework and UA sessions. Thank you in advance !

Abril Guanes 2A

In a UA Session, we learned that "covalent character increases going down a group". This makes sense because as you go down a group, atomic radius increases and electrons are further out, allowing them to be easily distorted. However, does this apply to Groups 1 and 2? I'm confused because...

Abril Guanes 2A

Correct! The last lecture that covers Midterm II material was the one from last Wednesday.

Abril Guanes 2A

When writing the electron configuration for Mn, [Ar]3d^5 4s^2. Although 4s subshell is filled first, when writing the electron configuration, the 4s subshell comes after because it has higher energy. This means that the electron will come off the last subshell in the electron configuration, which wo...

Abril Guanes 2A

Hello! You are correct in saying that the overall formal charge is -2 as indicated by the molecular formula. When doing the Lewis structure you would want to avoid putting any charge on carbon since it is the central atom. You can do this by doing a double bond with one of the oxygens. This would be...

Abril Guanes 2A

Hello! I was hoping someone could explain, when drawing a Lewis structure, how you know whether an OH/HO is going to be an O attached to the central atom and a hydrogen extending from the oxygen versus when the hydrogen and oxygen are both connected to the central atom. I've heard that OH means an o...

Abril Guanes 2A

Hello! The longer and probably the safest way is to write out the electron configuration for all the elements in the group it's asking for. This will probably take time, but it's good practice. When asking for the electron configuration, it's asking for the outermost electrons (including the electro...

Abril Guanes 2A

Hello! I have been to Lavelle's office hours and many UA workshops. All of them have said that Hydrogen boding is possible when the hydrogen is bonded to Nitrogen, Oxygen, or Fluorine. I'm not entirely sure as to why, and hopefully someone can provide that insight, but the general rule of thumb is w...

Abril Guanes 2A

I think something else to note is electronegativity. We know the trends for electronegativity looking at the periodic table. Ionic bonds happen between elements that have a very large electronegativity difference (so for example, opposite sides of the periodic table), but covalent bonds happen betwe...

Abril Guanes 2A

For a bond to be favorable, it means the bond has a very high negative energy (example, today in class with -250 kJ/mol). A very high negative energy means that the bond is releasing a lot of energy, rather than requiring a lot of energy, making it favorable.

Abril Guanes 2A

Chem_Admin wrote:Lily, I will go through this in my 3pm discussion section today.

I've included an imagine to clear it up!

Abril Guanes 2A

Can someone please explain what a dipole dipole bond is? We learned dipole moments however I have not heard dipole in any other context until this post. Hello! I am currently in Lavelle's office hours right now. He explained dipole dipole bonds in this manner. Suppose you have two water molecules. ...

Abril Guanes 2A

Generally, Lewis Structures with a formal charge of 0 are more stable than others with a positive or negative charge. Hope this helps!

Abril Guanes 2A

To add to the previous posts, Dr. Lavelle also mentioned a few elements have the ability to have an expanded octet, such as Sulfur, allowing it to have more electrons than the 8 that are inn the octet guideline, so keep an eye out for those when they are mentioned!

Abril Guanes 2A

Week 7 during discussion!

Abril Guanes 2A

I found this table that helps visualize it a little bit more clearly. I hope this helps!

Abril Guanes 2A

Hello! So, Dr. Lavelle touched it briefly, but he explained that for multi-electron atoms AFTER atomic number 20, the 4s state is higher in energy than 3d, meaning the electrons would first fill up the 3d orbital, and then the 4s. So the electron configuration for Mn would be [Ar]3d5 4s2. Because th...

Abril Guanes 2A

I also keep clicking on my name to view my points but it is not showing. Where do we click again to view our points? Hi! I think it's not directly on your name by right next to your name, on the left there is like a little paper followed by "by (insert name)". I think that means "Pos...

Abril Guanes 2A

From my understanding, the n1 and n2 are relatively arbitrary, meaning that yes you change them depending on whether you need a positive or negative answer, so absorption vs emission. I typically use the E= -hR/(n)^2 concept and just do final energy - initial energy. This may also be a way for you t...

Abril Guanes 2A

Awesome! Thanks :D

Abril Guanes 2A

Is there any way to check to see if you're getting your participation points through Chemistry Community? I tend to post 5-7 times a week, but I'm not sure if all my posts are "valid" posts to get points and was wondering if there was any way to find out? Thanks!

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