CHEMISTRY COMMUNITY

Kaitlyn Hernandez 3I

I believe its because C has the lowest activation energy.

Kaitlyn Hernandez 3I

A thermodynamically stable reaction has a negative delta G, meaning that its spontaneous. A thermodynamically unstable reaction has a positive delta G, meaning that its nonspontaneous.

Kaitlyn Hernandez 3I

This was very helpful, thank you!!! Dr. Lavelle also has some notes on his website that go over acid/base redox reactions and that really clarified a lot for me. I'll put the links down below: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Balancing_Redox_Reactions_Acidic_Conditio...

Kaitlyn Hernandez 3I

You can keep Celsius for this question because if the temperature rises by 2.49 degrees C, it also rises by 2.49 degrees K. For your second question, I believe you are right; q(reaction) = -q(calorimeter).

Kaitlyn Hernandez 3I

The reaction on the right will be reduction (cathode) and the reaction of the left will be oxidation (anode). So, the equation for E*cell = E(cathode)* - E(anode)*.

Kaitlyn Hernandez 3I

When K is small, reactants are favored over products. When K is big, products are favored over reactants.

Kaitlyn Hernandez 3I

I found a chem community post that explained this a few years back that was really helpful!!

Here is the link:
viewtopic.php?t=5450

Kaitlyn Hernandez 3I

I am looking forward to being on campus next year, especially after a long year not being able to go out and staying home! I also am very excited for in-person classes again, since it has been so long since we've had them! :)

Kaitlyn Hernandez 3I

I recommend So Good by Omar Apollo, Honey by Boy Pablo, Chinese Satellite by Phoebe Bridgers, Daydream by Luna Luna, and Don't Be a Fool by Dreamer Boy !! They all have a lot of underrated songs and are some of my favorite artists right now :)

Kaitlyn Hernandez 3I

I recommend Mochi Dochi!! It's a Korean hot dog restaurant in Sawtelle which is only 10-15 minutes away from campus :)

Kaitlyn Hernandez 3I

Step-up sessions usually cover conceptual concepts that we learned in lecture and then provide example problems that requires us to apply the conceptual knowledge. The workshops offer worksheets with more practice problems, similar to what we see in the textbook. I recommend attending step up sessio...

Kaitlyn Hernandez 3I

The equation you use depends on what values of E° you are using. If you are given the standard reduction potentials, then you should use E° cell = E° cathode - E° anode. The negative sign before the E° anode basically switches the value to be the standard potential of the oxidation reaction. If you...

Kaitlyn Hernandez 3I

I am satisfied with my Midterm 2 score, but knowing that I did make simple errors does make me a little disappointed since the questions are worth a lot of points. I definitely wish I focused on conceptual concepts more, but for now I am just going to continue with the assigned textbook problems and...

Kaitlyn Hernandez 3I

I know there are two equations for solving E° --> (1). E° cell = E° cathode - E° anode and (2). E° cell = E° reduction + E° oxidation. But how do we know when we have to use either equation to solve for E° or does it not matter which equation we use?

Kaitlyn Hernandez 3I

If you're willing to binge, Criminal Minds has 15 seasons!! I believe only the first 12 (I could be wrong) are on Netflix and the rest of the seasons are on Hulu.

Kaitlyn Hernandez 3I

I actually spent a lot of time on this problem (I had different molecules though!), but one of the concepts on the feedback on Sapling helped me solve this problem. One of the other methods for balancing in a basic solution is to skip the acidic rule step. If you need x atoms of Oxygen on one side o...

Kaitlyn Hernandez 3I

For cell diagrams, I believe that anodes are typically on the left and cathodes are typically on the right. Electron flow is always from the anode (oxidation) to the cathode (reduction).

Kaitlyn Hernandez 3I

I plan on getting a lot of sleep this weekend and catching up on episodes of The Bachelor that I am behind on! Other than that, last night I treated myself by baking chocolate chip cookies :)

Kaitlyn Hernandez 3I

When Delta H is + and Delta S is +, the reaction is spontaneous only if Delta H is less than TDeltaS . When Delta H is + and Delta S -, the reaction is never spontaneous . When Delta H is - and Delta S is -, the reaction is spontaneous only if Delta H is greater than TDelta S . When Delta H is - and...

Kaitlyn Hernandez 3I

Here are some examples of open, closed, and isolated systems! Open: plants conducting photosynthesis, boiling water without a lid, an open cup of coffee Closed: boiling water with a lid, a closed water bottle, a cup of coffee with a lid Isolated: the universe, a thermos flask Something to remember a...

Kaitlyn Hernandez 3I

Heat capacity can be defined as the amount of heat that is required to raise the temperature of a certain substance. The equation to calculate heat capacity is q/delta T.

Kaitlyn Hernandez 3I

First, you need to find the overall enthalpy of formation of the entire reaction. To recap, that'd be the sum of the enthalpy of formation of products minus the sum of the enthalpy of formation of reactants. That answer should should be -13168 KJ/mol. Next, you need to divide the previous value by ...

Kaitlyn Hernandez 3I

I do mindfulness meditation every night before I go to sleep, because it helps me reflect on my day and identify the good parts of my day and places in which I need to improve :) I also value sleep a lot and I use a sleep calculator to help me plan out my nights! All you have to do is put in the tim...

Kaitlyn Hernandez 3I

Hannah_Butler_2E wrote:
Madeline Ogden 3B wrote:qrev is the amount of heat generated in a reversible process.

So does deltaS = q/T only apply to reversible expansions and compressions?

I believe you use this equation when you are at a constant temperature for a reversible process.

Kaitlyn Hernandez 3I

For now, I am being optimistic, because we still have a lot of time to study for Midterm 2 and many step-up and UA sessions to attend this week! There is still a lot to do in terms of studying, but I know we all can do it :) But for now, I am just completing textbook problems and practice problems, ...

Kaitlyn Hernandez 3I

You have to approach this problem in three different steps. First, you should find the delta S when heating the water from 44.0 degrees C to 100 degrees C. Next you should find the delta S when cooling the water from 100 degrees C to 44.0 degrees C. You are already given the standard molar entropy o...

Kaitlyn Hernandez 3I

Professor Lavelle hasn't informed us exactly what Midterm 2 will cover, but I'm assuming it will cover weeks 4-6 lectures! A good idea would be to to start reviewing lectures starting week 4, since we know for sure those will be on the midterm.

Kaitlyn Hernandez 3I

I plan on taking chem 14C next quarter along with anatomy and another course, but I am unsure of what my 3rd class should be. Do you guys have any recommendations? I heard Scand 50 was a good class but I also heard that it fills up fast. I was thinking of taking Scand 50 too! But I am also consider...

Kaitlyn Hernandez 3I

You're going to use the equation (Delta u) = q + w. You are already given q (Delta H), so you should use the equation w = -deltanRT where n = 1.00 mol, R = 8.314 J x K^-1 x mol^-1, and T = 298K. Remember to convert this value from J to kJ. After you solve for w, all you have to do is plug your value...

Kaitlyn Hernandez 3I

You should look at the number of the moles of gases when determining which are doing work and which are not. The correct answers would be the equations that produce more moles of gas than what is used up in the reaction, because this results in a negative w.

Kaitlyn Hernandez 3I

Reversible reactions cause a very slow change in volume and occur when the system can restored to its initial state (in other words, it can be reversed).

Kaitlyn Hernandez 3I

What was the first step that you did in this problem? Given 53.8 g of ice, you have to convert this to mol ice and multiply it by delta H fusion (6.01 x 10^3 J/mol) to get the amount of heat required to melt the ice. Then you need to solve for q (ice) and q (water). So, your final equation to solve ...

Kaitlyn Hernandez 3I

^ I agree with Tikva. Sapling problems are really helpful when you want more practice with problems that are similar to textbook problems! The solutions are also really helpful as well so you can see every step you need to solve a similar problem :)

Kaitlyn Hernandez 3I

Textbook, textbook, textbook problems!!! In other words, redo textbook problems until you can finally get the answer without looking at the answer key or your notes. This will make sure that you KNOW the material in and out. I like to create notes for each outline too so I can just have all of the c...

Kaitlyn Hernandez 3I

I definitely understand where you're coming from, the midterm was definitely challenging! All you can do now is focus on the future and make sure to attend as many sessions as possible for the next midterm or final. There are plenty of opportunities to improve your grade :))

Kaitlyn Hernandez 3I

I lost an electron. You really have to keep an ion them :(

Kaitlyn Hernandez 3I

I took a FAT nap after the midterm and then I decided to bake some brownies to celebrate finishing off the first week of midterms for this quarter! I decided to just rest for the day, so that I wouldn't overwhelm myself :)

Kaitlyn Hernandez 3I

I believe there's a recommended method we should use for certain problems. For example, we use Hess's Law when we have to find the reaction enthalpy for a specific chemical equation, given a few chemical equations and their delta Hs that we have to manipulate to get the desired chemical equation. We...

Kaitlyn Hernandez 3I

The Daily Bruin actually has a section that gives you the estimations of how quickly a class fills up at UCLA! You can test it out here:

https://stack.dailybruin.com/2020/02/05/class-fill-ups/

Kaitlyn Hernandez 3I

You will take the anti-log whenever you are given pKa and you need Ka, pKb and you need Kb, pOH and you need [OH-], and pH and you need [H3O+]! The anti-log is as simple as taking 10^-(value you are given). Hope that makes sense!

Kaitlyn Hernandez 3I

When determining whether or not to use Ka or Kb when calculating the pH of a salt solution, you should determine if you have a more acidic solution or a more basic solution. In situations in which you are given Kb yet your solution is more acidic, you can use the simple equation Kw = Ka x Kb and you...

Kaitlyn Hernandez 3I

Ka and pKa are two ways to measure the strength of an acid. A high Ka and a low pKa indicates a strong acid. Kb and pKb are two ways to measure the strength of a base. A high Kb and a low pKb indicates a strong base.

Kaitlyn Hernandez 3I

That is the correct concentration of CH3NH3Cl. Did you set up your equation as $\frac{x^2}{0.511-x}=2.8x10^{-11}$ ? When you set it up like this, you should get a value for x and then you have to plug that value in -log(x) to get the pH.

Kaitlyn Hernandez 3I

I really like indie pop music! Some of my favorite songs at the moment include Lovesong by Charlie Burg, Sofia by Clairo, Puppy Dog by Dreamer Boy, and Sunshine and [censored] are no Longer Enough by Luna Luna. One of my anthems this year has been Good Days by SZA though :))

Kaitlyn Hernandez 3I

You can solve this problem by finding the pOH of the solution (pOH = 14 - pH) and then using the pOH to solve for [OH-]. Then you can work backwards to solve for the unknown concentrations.

Kaitlyn Hernandez 3I

I like to break the molecule up into two parts. For example, for LiClO4, we can break this up into Li and ClO4. Based on the chart for strong acids and strong bases, we know that Li comes from the strong base, LiOH, and ClO4 comes from the strong acid, HClO4. Since they are both strong, they cancel ...

Kaitlyn Hernandez 3I

In case you can't find it, here's the link for the new constants and formulas sheet! I'd be sure to have this printed with a periodic table and some scratch paper before the midterm :)

https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf

Kaitlyn Hernandez 3I

Yes, steam causes severe burns because it is releasing heat. Dr. Lavelle explained in lecture that this occurs due to water's large enthalpy of vaporization / large negative enthalpy of condensation.

Kaitlyn Hernandez 3I

For future reference, Lavelle has this document on his website with any errors in the solution manual for textbook problems!!

https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf

Kaitlyn Hernandez 3I

I was curious about this question too. But I looked at my lecture notes, and since [H2O] is in large excess, we consider the concentration to be unchanged and therefore, we don't include it in the equation.

Kaitlyn Hernandez 3I

To start this problem, you should create an ICE table. PCl3 Cl2 PCl5 I 0 0 0.0250 C +x +x -x E x x 0.0250 -x Then plug in these values in to the Kp expression to solve for X. Kp = \frac{P(PCl5)}{P(PCl3)P(Cl2)} = 393 Solve for x and then plug that answer back into the equilibr...

Kaitlyn Hernandez 3I

Q is the reaction quotient and K is the equilibrium constant. When determining the direction a reaction is going to proceed, you have to compare your Q and K values. So, If Q is less than K, then the forward reaction is favored. If Q is greater than K, then the reverse reaction is favored. When Q is...

Kaitlyn Hernandez 3I

I would assume that the our midterms for 14B are structured in a similar way as they were in 14A, so I believe that they would be multiple choice. However, I don't think Lavelle has officially announced whether or not it is multiple choice so that would definitely be subject to change :)) Also yes, ...

Kaitlyn Hernandez 3I

Personally, I set a specific schedule of what I need to get done each day and I make sure that I am motivated to keep up with this schedule to make sure that I am getting my work done. Another thing I like to do is to redo textbook problems until I am able to solve them without looking at the soluti...

Kaitlyn Hernandez 3I

I'm pretty sure that Outline #4 is dedicated to thermodynamics.

https://lavelle.chem.ucla.edu/wp-conten ... namics.pdf

Kaitlyn Hernandez 3I

Sapling homework is always mandatory. I believe the Sapling problems for the chemical equilibrium outline are due next Sunday (1/17). However, textbook problems aren't necessarily mandatory, but HIGHLY recommended to complete. I took 14a last quarter with Lavelle and I found the textbook problems to...

Kaitlyn Hernandez 3I

For part a, you should first form a balanced equation and find the initial concentration of Cl2 (g). The balanced equation is then Cl2 (g) -> 2Cl (g) and the initial concentration of Cl2 (g) would be 0.0020 mol Cl2 / 2.0 L to get 0.0010 M. The ice table is then set up like this: concentration Cl2 2C...

Kaitlyn Hernandez 3I

Faith St Amant 3D wrote:Here's how my TA worked through it. You just need to add the two reactions shown from the table together, and then multiply their K values.

Is there a specific reason why you have to multiply their K values?

Kaitlyn Hernandez 3I

The ideal gas is a theoretical concept and is used to guide us with calculations and make estimations. Khan Academy has a video that I found to be really helpful in explaining the definition and application, I recommend watching it! Here's the link: https://www.khanacademy.org/science/class-11-chemi...

Kaitlyn Hernandez 3I

Tanya Bearson 2K wrote:Thank you all for the tips! Are we allowed to use TI-84 calculators on exams?

If I am correct, I believe we are able to use any calculator for tests.

Kaitlyn Hernandez 3I

Ideal gases are exactly that: they're ideal and theoretical and they follow all of the gas laws regardless of the conditions they're in. I believe that the ideal gas law really helps us with calculations about properties and behaviors of gases.

Kaitlyn Hernandez 3I

I would attend as many as you can in the beginning to see which UA is best for your learning style! After you figure out who works best, I'd suggest attending one or two per week. When midterms come around, I would recommend doubling that just to get extra practice if you need it :)

Kaitlyn Hernandez 3I

To study for the midterms, I would write outlines of what was covered to help me study. I think I am going to try to start on these earlier so that I am always reviewing the material from the previous lectures :) Also attending more UA sessions if I'm ever unclear on anything.

Kaitlyn Hernandez 3I

I plan on taking lots of naps to catch on sleep and catching up on tv shows I stopped watching when school started! I also plan on making more playlists to expand my music library :)

Kaitlyn Hernandez 3I

Are bases made from Group 1 elements stronger or weaker than bases made from Group 2 elements?

Kaitlyn Hernandez 3I

I plan on doing self-care meditation to really just relax all the stress that's been building up over this week for this final :) And also binge watching Netflix and Disney+ since I am so behind on a lot of the shows I like to watch!

Kaitlyn Hernandez 3I

I made my own outline notes of each outline that we covered in class, and I'm probably going to just review them as often as I can to make sure that I retain all of the information! Also doing practice problems over break could help too. Personally, I am going to focus on acids and bases a little bi...

Kaitlyn Hernandez 3I

Here's the Google Drive folder he gave us with all of his previous worksheets :)) https://drive.google.com/drive/folders/ ... sp=sharing

I believe each worksheet has a link to to their corresponding key.

Kaitlyn Hernandez 3I

H is bonded to O in HClO3 because that's the most stable structure. With this structure, each atom has a formal charge of 0. If H was bonded to the Cl, the O without the double bond would have a formal charge of 0 and the Cl would have a formal charge of +1. Also, I believe since HClO3 is an acid, t...

Kaitlyn Hernandez 3I

I would just understand the definitions of all of them to be the most prepared for the final! We've definitely covered more of Bronsted acids/bases and Lewis acids/bases in lecture and in textbook problems, though, I think it would just depend on what the question is asking.

Kaitlyn Hernandez 3I

a) To find the desired pH, you have to take -log of the concentration. So solve -log(0.025) = the desired pH. b) To find the actual pH, you have to consider the mistake that was made by the laboratory technician. To find the concentration, you should take 0.025 x \frac{200 mL}{250 mL} . Then take th...

Kaitlyn Hernandez 3I

Our evaluations are anonymous, so I don't think there's a way for him to know whether or not we completed them. But also since he didn't say anything about it, it's likely a no

Kaitlyn Hernandez 3I

Here's a PDF I found that lists the most common strong acids and strong bases! I think it's helpful to use this as a resource when deciding :) https://www2.palomar.edu/users/ngeetha/110labhandouts/TABLE%20OF%20STRONG%20ACIDS%20and%20bases.pdf Another thing to consider is the shape of the molecule. T...

Kaitlyn Hernandez 3I

The roman numeral for a transition metal is its charge/oxidation state. To figure it out, you can use this equation my TA provided us in discussion last week: (# of metal atoms)(oxidation # of metal) + sum of (# of each ligand)(charge of ligand) = charge of ion and then you can just rearrange the fo...

Kaitlyn Hernandez 3I

A little bit stressed for finals! But I've been meditating and taking time for myself as well to ensure that I don't overwhelm myself too. Hope everyone is doing well :)

Kaitlyn Hernandez 3I

I don't think we've learned how to do this in Chem14A, I believe we'd just put tetrahedral or square planar for the compound shape. I was looking back at a few practice problems I did at a Step-Up session and that's what the UA put as the shape of a compound with a coordination number of 4 !

Kaitlyn Hernandez 3I

The sigma bonds allow for rotation in a chelate ! So yes, you're correct. I believe sigma bonds are able to do this because the electrons are located in a cylindrically symmetrical cloud along the axis while pi bonds do not allow the atoms to rotate.

Kaitlyn Hernandez 3I

In this situation, I'd follow what the textbook says. HClO3 is a strong acid.

Kaitlyn Hernandez 3I

I'm not sure if we need to know exactly which bond in a double or triple bond is sigma or pi, but I'd suggest memorizing the patterns of sigma and pi bonds. So,
Single Bond = 1 sigma bond
Double Bond = 1 sigma bond + 1 pi bond
Triple Bond = 1 sigma bond + 2 pi bonds

Kaitlyn Hernandez 3I

In PCl5, P has 10 bonding electrons, thus an expanded octet. Typically elements in Period 3 or higher are allowed to have an expanded octet because they have d orbitals that can accommodate any extra electrons.

Kaitlyn Hernandez 3I

Attend step-up sessions if you're confused! I attended one before MT2 and before I did, I. was so confused on intermolecular forces but after, it was really helpful for me to understand :) Something I like to do is go over my lecture notes again and condense them onto one document where I include th...

Kaitlyn Hernandez 3I

Here's another helpful document that I've been using to help me study molecular shape!

https://www.angelo.edu/faculty/kboudrea ... _VSEPR.pdf

Kaitlyn Hernandez 3I

I personally find them really helpful! I recently started going to Hannah's step up session on Tuesdays from 2 to 4pm and she's been really helpful in explaining the concepts. She usually posts a worksheet that in the chat from google drive and I just copy that onto my iPad so I can write directly o...

Kaitlyn Hernandez 3I

They should be covered before the final, I believe that we just started Outline 5 with Wednesday's lecture :)

Kaitlyn Hernandez 3I

I believe that they are interchangeable, radicals (or free radicals) are atoms with at least one unpaired valence electron.

Kaitlyn Hernandez 3I

First, you should draw the Lewis structure to help you answer these questions! For part A: The shape of a thionyl chloride molecule is trigonal pyramidal. We know this because there are 3 bonding pairs and 1 lone pair when we draw the Lewis structure of SOCl2. For part B: We know that the angles are...

Kaitlyn Hernandez 3I

Lillian Ma 1L wrote:I believe that it is a sp3 hybridization.

How can we figure out the hybridization of an atom? Do we just need to determine the shape through the VSEPR model?

Kaitlyn Hernandez 3I

Maybe try looking online for good diagrams of how VSEPR shapes look and then put those pictures in your notes so you can always refer back to them when you're studying. I definitely get where you are coming from though, visuals are so much more helpful in helping us remember these shapes!

Kaitlyn Hernandez 3I

I enjoy going on walks around sunset so I can watch the sunset go down! It's so calming, especially since there's a nice view from my house :) During the day, I enjoy playing volleyball with my friends just to take a break from any school work that I have too!

Kaitlyn Hernandez 3I

Lewis bases donate electron pairs, which means that they are more likely to have a lone pair of electrons, such as NH3 or OH. In most cases, anions are Lewis bases. Lewis acids accept electron pairs, and I believe that in most cases, cations are Lewis acids, such as H+.

Kaitlyn Hernandez 3I

We know that the ionic radius follows the same trends as the atomic radius: the ionic radius decreases across a period and increases down a group. Since these ions are isoelectronic, we have to look at the size of each one to determine increasing size. Following the ionic radius trend, we know that ...

Kaitlyn Hernandez 3I

I went to Hannah Chew's Step Up session last Tuesday and she was really helpful in explaining covalent character. Basically, the smaller the cation, the greater covalent character and the larger the anion, the greater covalent character as well. I'll explain some of the few examples she had us do! B...

Kaitlyn Hernandez 3I

I don't believe that it'll always be that specific in every situation, but I'd just try to always remember that in order of increasing length, bond lengths are: triple bonds < double bonds < single bonds.

Kaitlyn Hernandez 3I

Attend Step-Up sessions! I went to one this past Tuesday and it was VERY helpful in helping me understand intermolecular forces more. Also, make sure to memorize the conceptual concepts, especially since a lot of the last couple of outlines have been conceptual. I'd suggest redoing practice problems...

Kaitlyn Hernandez 3I

There are 8. In addition to the 4 Hydrogen bonds that can be formed from the hydrogen atoms bonded to nitrogen, nitrogen has one pair of unpaired electrons and can form a hydrogen bond from that pair. Because there are two nitrogen atoms, 2 hydrogen bonds can be formed. Oxygen has two pairs of unpai...

Kaitlyn Hernandez 3I

I believe that all molecules have london dispersion forces. The strength of these forces increase with the number of electrons (larger molecules have stronger forces).

Kaitlyn Hernandez 3I

I am going to be focusing on textbook problems and making sure I can independently do each problem without looking at my notes. I also plan on doing the same for Sapling. Good luck!

Kaitlyn Hernandez 3I

Veronica Macias 3C wrote:Does polarizability have anything to do with electronegativity?

Polarizability decreases as an atom / ion gets smaller and more electronegative. So when you are looking at a periodic table, it increases down a group and decreases across a period, which is the opposite trend of electronegativity.

Kaitlyn Hernandez 3I

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

How can we figure out whether or not a molecule has dipole-dipole interactions? I understand that (a) and (e) are no, but how can we identify the other three?

Kaitlyn Hernandez 3I

According to the textbook, highly polarizable atoms and ions are usually large anions, because there would be a greater distortion on its electron cloud. So, polarizability would follow the opposite trends as electronegativity. Polarizability is more defined as how easily an atom's electron cloud is...

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