Search found 97 matches

by TJ Lai 2H
Sun Feb 28, 2021 6:00 am
Forum: Administrative Questions and Class Announcements
Topic: LS7a
Replies: 11
Views: 73

Re: LS7a

I took it with Maloy last quarter, and he was terrific! He was a super clear lecturer, and explained everything in a really accessible way. I retained practically zero information from my bio class and still did well. My main tips for this class are to really go over the practice exam questions on l...
by TJ Lai 2H
Sun Feb 28, 2021 5:41 am
Forum: Student Social/Study Group
Topic: Pre-Med Advice
Replies: 6
Views: 101

Re: Pre-Med Advice

viewtopic.php?f=157&t=21765
viewtopic.php?f=157&t=45665

There's some really great advice in these threads!
by TJ Lai 2H
Sun Feb 28, 2021 5:39 am
Forum: Administrative Questions and Class Announcements
Topic: summer session classes
Replies: 17
Views: 85

Re: summer session classes

Janna Shakiba wrote:Does anyone know if chem 14D is being offered this summer?


I don't think it will be.
by TJ Lai 2H
Sun Feb 28, 2021 5:38 am
Forum: Student Social/Study Group
Topic: Final
Replies: 43
Views: 101

Re: Final

I'm going to go through all of the homework problems again and really note what kinds of mistakes I make.
by TJ Lai 2H
Sun Feb 21, 2021 2:15 pm
Forum: Administrative Questions and Class Announcements
Topic: Can We Review our Exams?
Replies: 69
Views: 247

Re: Can We Review our Exams?

Your TA can't show you the questions, but they read you the questions to you that you missed and go over them with you verbally
by TJ Lai 2H
Sun Feb 21, 2021 2:13 pm
Forum: Student Social/Study Group
Topic: Culinary Chemistry
Replies: 69
Views: 412

Re: Culinary Chemistry

This is such a great thread! I love cooking and it's really cool to apply things I learned in chem class to my cooking :)
by TJ Lai 2H
Sun Feb 21, 2021 2:10 pm
Forum: Administrative Questions and Class Announcements
Topic: Textbook Problems
Replies: 8
Views: 39

Re: Textbook Problems

Here's a link to the solution manual errors: I think it gets updated pretty regularly so it's good to have the newest versions

https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
by TJ Lai 2H
Sun Feb 21, 2021 2:07 pm
Forum: Administrative Questions and Class Announcements
Topic: summer session classes
Replies: 17
Views: 85

Re: summer session classes

I did want to add that while saving a spot right now is probably a good idea, UCLA does charge you a $150 "processing fee" if you drop all of your summer session classes so make sure you are committed to taking at least 1 class over the summer. https://summer.ucla.edu/academiccourses/onlin...
by TJ Lai 2H
Sun Feb 21, 2021 1:54 pm
Forum: Student Social/Study Group
Topic: Preparing
Replies: 24
Views: 85

Re: Preparing

Agree with everyone else who suggested YouTube lectures, those have always been super helpful for me when I need extra explanations on a confusing topic.
by TJ Lai 2H
Sun Feb 14, 2021 7:51 pm
Forum: Student Social/Study Group
Topic: Silly Mistakes?
Replies: 60
Views: 291

Re: Silly Mistakes?

I totally need this :( This is how I felt about MT1 as well. Overall I thought I knew/ prepped the material well, but I made so many silly mistakes. I need to work on 1) Slowing down to read the question better and 2) Being more forgiving of myself. Thanks for posting this!
by TJ Lai 2H
Sun Feb 14, 2021 7:50 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 Question #
Replies: 5
Views: 45

Re: Midterm 2 Question #

Don't think this info has been released yet, but I'm grateful for the 2 bonus questions on this midterm!
by TJ Lai 2H
Sun Feb 14, 2021 11:03 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture #16 Error
Replies: 6
Views: 34

Re: Lecture #16 Error

This happens to me a lot. I usually just keep refreshing every now and then and it will eventually re-appear for me.
by TJ Lai 2H
Sun Feb 14, 2021 11:03 am
Forum: Administrative Questions and Class Announcements
Topic: Monday Holiday Workshops
Replies: 3
Views: 26

Re: Monday Holiday Workshops

Yes, there's 2 1-hour workshops on Monday (Jacqueline Jiang 12-1 PM/ Michelle Nguyen 1-2 PM)
by TJ Lai 2H
Thu Feb 11, 2021 6:19 am
Forum: Administrative Questions and Class Announcements
Topic: cc update
Replies: 23
Views: 125

Re: cc update

My hasn't been updated either, but just wait it out :) They will definitely be updated eventually.
by TJ Lai 2H
Sun Feb 07, 2021 12:50 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Saping 3/4 #14
Replies: 1
Views: 22

Re: Saping 3/4 #14

For part A, you want to use the equation w = -n*R*T*ln(V2/V1). To do so, you will first need to find the number of moles n using the equation n = pV/RT (derived from the equation pV = nRT). Be sure to use the correct ideal gas constant (check your units). In this case, it would be R = 8.206 * 10^-2 ...
by TJ Lai 2H
Sun Feb 07, 2021 12:11 pm
Forum: Student Social/Study Group
Topic: Students Who Have a Job
Replies: 79
Views: 332

Re: Students Who Have a Job

I'm starting a part-time job next quarter and will also be balancing classes, so this has been a helpful thread for me :) Feeling nervous, but hopefully I can pull it off...
by TJ Lai 2H
Sun Feb 07, 2021 12:06 pm
Forum: Administrative Questions and Class Announcements
Topic: Translational, Rotational, Vibrational energy
Replies: 2
Views: 13

Re: Translational, Rotational, Vibrational energy

I don't think Dr. Lavelle would test us on topics we don't cover in class/ outlines/ hw
by TJ Lai 2H
Thu Feb 04, 2021 11:54 am
Forum: Administrative Questions and Class Announcements
Topic: Sapling Weeks 3,4,5 Grade Error
Replies: 4
Views: 43

Re: Sapling Weeks 3,4,5 Grade Error

Sometimes it takes awhile for my Sapling grade to update (it sometimes takes a day or so for me). I wouldn't be too worried about it.
by TJ Lai 2H
Wed Feb 03, 2021 6:33 pm
Forum: Administrative Questions and Class Announcements
Topic: Tips for Concentrating during a test
Replies: 31
Views: 102

Re: Tips for Concentrating during a test

I have the same problem!! It's really hard for me to have a quiet work environment during tests as there is always tons of noise in my house and the walls are super thin :( I try to tell people to leave me alone / be quiet during my exam times but invariable some always starts playing music/ talking...
by TJ Lai 2H
Sat Jan 30, 2021 5:24 am
Forum: Administrative Questions and Class Announcements
Topic: 14BL and CL
Replies: 13
Views: 135

Re: 14BL and CL

I would also like to know the answer to this! Building off of this, how many hours would you say that you spend on the labs (class time + assignments) each week?
by TJ Lai 2H
Thu Jan 28, 2021 7:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook 4.31
Replies: 4
Views: 42

Re: Textbook 4.31

In my textbook it's written as C(s), graphite
Screenshot 2021-01-28 223517.png
Screenshot 2021-01-28 223517.png (10.3 KiB) Viewed 26 times
by TJ Lai 2H
Thu Jan 28, 2021 6:24 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook 4.31
Replies: 4
Views: 42

Re: Textbook 4.31

The enthalpy of formation of graphite C(s) is 0 kJ/mol. You can look up this value in Appendix 2 in the textbook.
by TJ Lai 2H
Wed Jan 27, 2021 1:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4.31: Hess's Law vs. Bond Enthalpies
Replies: 2
Views: 42

4.31: Hess's Law vs. Bond Enthalpies

Screenshot 2021-01-27 162421.png When I first approached this question, I calculated the change in enthalpy using the sum of bond enthalpy changes. On the products side, we break two O-H bonds (2 * 463). On the reactants side, we form one H2 bond (-436) and one CO bond (-1074). Once I added these b...
by TJ Lai 2H
Tue Jan 26, 2021 5:30 pm
Forum: Administrative Questions and Class Announcements
Topic: posting screenshots
Replies: 4
Views: 56

Re: posting screenshots

Once you've dragged your screenshots into the window, you can click "place inline" at the bottom where it says "Attachments," and the image will appear in your text.
by TJ Lai 2H
Mon Jan 25, 2021 6:42 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook 4D.21 c
Replies: 1
Views: 23

Re: Textbook 4D.21 c

I got the same answer as you, and looking at the solutions manual, I'm pretty sure there is either something wrong in the solutions manual or in Appendix 2A. The enthalpy of formation for K2S(aq) given in the Appendix 2 is -471.5 kJ/mol, but is given as -417.5 kJ/mol. So it just looks like a typo to...
by TJ Lai 2H
Mon Jan 25, 2021 6:39 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.21 part C
Replies: 4
Views: 38

Re: 4D.21 part C

I'm pretty sure this is a solutions manual error. The enthalpy of formation for K2S(aq) given in the Appendix 2 is -471.5 kJ/mol. However, in the solutions manual it is given as -417.5 kJ/mol.
by TJ Lai 2H
Sat Jan 23, 2021 6:30 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 1 Outline 3
Replies: 3
Views: 33

Re: Midterm 1 Outline 3

From his email on Friday: "Midterm 1 covers Chemical Equilibria, Acid and Base Equilibria, and only these Week 3 topics (4D.3; 4D.4; 4D.5; 4E.3)"
by TJ Lai 2H
Thu Jan 21, 2021 6:34 am
Forum: Administrative Questions and Class Announcements
Topic: Where to find textbook answers
Replies: 4
Views: 28

Re: Where to find textbook answers

Also sometimes the textbook solutions aren't entirely accurate --you can find some solution manual errors listed here: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
by TJ Lai 2H
Thu Jan 21, 2021 6:31 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Lower pkb is more basic
Replies: 4
Views: 40

Re: Lower pkb is more basic

Going off of that, pkb = -log(kb). Because it is a negative log value, lower values of pkb imply higher levels of kb. Likewise, because kb is a measure of dissociation of the base [B+][OH-]/[BOH], a higher kB means that more of the base has dissociated -> more basic. Thus, lower pkb values -> more b...
by TJ Lai 2H
Tue Jan 19, 2021 4:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week 2 #5
Replies: 4
Views: 44

Re: Sapling Week 2 #5

You can start by using the pH to determine the pOH (pOH = 14-pH). With the pOH, you have the OH- concentration which is also the concentration that is protonated [BH+]. You would then divide this concentration [BH+] by ([BH+] + [B]) to solve for the percentage that is protonated. You can solve for [...
by TJ Lai 2H
Mon Jan 18, 2021 8:31 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.7
Replies: 3
Views: 27

Re: Textbook 6D.7

I'm not sure exactly why you are getting the answers that you have, but if you set the equation for part A as 3.0 x 10^-8 = (2.512 x 10^-5)^2 / (x - 2.512 x 10^-5) Since 3.0 x 10^-8 is a very small number, you can approximate this as 3.0 x 10^-8 = (2.512 x 10^-5)^2 / X Solving for X would result in ...
by TJ Lai 2H
Thu Jan 14, 2021 7:31 am
Forum: Student Social/Study Group
Topic: New Joke Chain
Replies: 46
Views: 214

Re: New Joke Chain

Nick P 3D wrote:H2O is water and H2O2 is hydrogen peroxide.
What is H2O4?

Drinking


Can someone explain this joke? I don't get it :(

Same with this from lecture yesterday:

Screenshot 2021-01-14 103034.png
by TJ Lai 2H
Thu Jan 14, 2021 7:13 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework problem 6B.9
Replies: 3
Views: 50

Re: Homework problem 6B.9

Dr. Lavelle said that there was a typo in this question, and we shouldn't do it. See the solutions manual errors PDF: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
by TJ Lai 2H
Wed Jan 13, 2021 6:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Temperature & K for Acids and Bases
Replies: 4
Views: 33

Re: Temperature & K for Acids and Bases

I'm not sure what you mean by "does the 25 degrees Celsius always hold for strong acid or base reactions," but the values of K do depend on temperature. If you are asking whether temperature influences whether the reaction contains a strong acid or base, it doesn't.
by TJ Lai 2H
Tue Jan 12, 2021 3:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling 5
Replies: 4
Views: 52

Re: Sapling 5

Think about how you would manipulate the given equations to arrive at 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g) You could start by looking for the first term in the above equation, 2NH3, in one of the given equations. Notice that the given equation N2(g)+3H2(g)↽−−⇀2NH3(g) contains 2NH3, and you can get 2NH3 on...
by TJ Lai 2H
Fri Jan 08, 2021 7:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Focus Exercise 5.39 Question
Replies: 2
Views: 63

Re: Focus Exercise 5.39 Question

I was also confused about this question... could someone clarify? My guess is there is an error for the Kc value that's not noted in the solutions manual error? Also my textbook says "In Table 5E.2..." which I'm pretty sure is a mistake because I don't think "Table 5E.2" exists. ...
by TJ Lai 2H
Fri Jan 08, 2021 7:02 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium_Textbook Problem_5G.5
Replies: 3
Views: 35

Re: Chemical Equilibrium_Textbook Problem_5G.5

NP! I'm really curious as to how to answer this question now... Does anyone have an idea of how to approach part a? How can we tell which is at equilibrium with out knowing Kc/ equilibrium equation?

Screenshot 2021-01-08 100104.png
by TJ Lai 2H
Wed Jan 06, 2021 7:43 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: adding chemical equations
Replies: 2
Views: 30

Re: adding chemical equations

You can refer to table 5G.2 to see how you might arrive at the equation you are trying to solve the K for through any combination of reactions listed in Table 5G.2. You may have to manipulate the equations in this table to get at your equation such as reverse the reactions, changing the coefficients...
by TJ Lai 2H
Wed Jan 06, 2021 7:21 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concept Clarification About Equilibrium Constants
Replies: 3
Views: 56

Re: Concept Clarification About Equilibrium Constants

We want the equilibrium constant K to be unitless. Dividing by standard pressure cancels out the units (bar) in each term so that we end up with a unitless K.
by TJ Lai 2H
Wed Jan 06, 2021 7:15 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium_Textbook Problem_5G.5
Replies: 3
Views: 35

Re: Chemical Equilibrium_Textbook Problem_5G3

I'm not really sure how to approach this question either so I would also like to hear if anyone has an idea (how can we tell which flask is at equilibrium without having the reaction equation /knowing the concentrations at equilibrium?). However, I did want to say that I think you are looking at pro...
by TJ Lai 2H
Wed Jan 06, 2021 7:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Forward vs Reverse Reactions
Replies: 3
Views: 26

Re: Forward vs Reverse Reactions

My understanding is that when you add more reactant to an reaction that is already at equilibrium, the reaction shifts to the right (forward reaction) and more product is produced, allowing the reaction to regain equilibrium. However, when you add more product to an equation that is already at equil...
by TJ Lai 2H
Sat Dec 12, 2020 7:02 am
Forum: Lewis Acids & Bases
Topic: Conjugate base of Boric Acid (6.13)
Replies: 1
Views: 60

Conjugate base of Boric Acid (6.13)

Could someone explain to me why the conjugate base of Boric acid has an added OH pairing, rather than removing an H (donating a proton)?
Screenshot 2020-12-12 095906.png
by TJ Lai 2H
Fri Dec 11, 2020 4:34 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: formic and acetic acid
Replies: 4
Views: 55

Re: formic and acetic acid

How do we know that the CH3 in acetic acid is electron donating?
by TJ Lai 2H
Wed Dec 09, 2020 12:34 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Videos Not Playing [ENDORSED]
Replies: 16
Views: 158

Re: Lecture Videos Not Playing [ENDORSED]

I've been experiencing the same issue. However, I just tried the second video (Play 2) and it seems to be working (for both Monday 12/7 and 12/9 lectures)! -Matt I've been trying Play 2 but unfortunately it hasn't been working for me either. For some confusing reason the videos work at certain time...
by TJ Lai 2H
Wed Dec 09, 2020 12:33 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Videos Not Playing [ENDORSED]
Replies: 16
Views: 158

Re: Lecture Videos Not Playing [ENDORSED]

TJ Lai 2K wrote:Not sure if this will work for everyone, but it's working for me now with the Cisco UCLA VPN turned on.


Nvm it stopped working for me again :(
by TJ Lai 2H
Wed Dec 09, 2020 12:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Videos Not Playing [ENDORSED]
Replies: 16
Views: 158

Re: Lecture Videos Not Playing [ENDORSED]

Not sure if this will work for everyone, but it's working for me now with the Cisco UCLA VPN turned on.
by TJ Lai 2H
Wed Dec 09, 2020 10:52 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture Videos Not Playing [ENDORSED]
Replies: 16
Views: 158

Re: Lecture Videos Not Playing [ENDORSED]

I am having this error too... tried switching to a different browser but nothing has worked. Has anyone figured out a way to fix this?
by TJ Lai 2H
Wed Dec 09, 2020 9:43 am
Forum: Significant Figures
Topic: 12/07 Lecture sig figs
Replies: 4
Views: 82

12/07 Lecture sig figs

Screenshot 2020-12-09 122729.png During Monday's lecture Dr. Lavelle, said that the sig figs for the answer to the above question is equal to the number of figures after the decimal point of 4.22 (2 sig figs), resulting in the answer 6.0 * 10^-5. I had thought that the number of sig figs for 4.22 i...
by TJ Lai 2H
Mon Dec 07, 2020 8:52 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Topic 9C Exercises Question 5
Replies: 7
Views: 87

Re: Topic 9C Exercises Question 5

You can usually tell if something is polydentate if the atom follows the structure Lone pair - spacer - spacer- lone pair. So for example in ox, it has an oxygen with a lone pair carbon as a spacer another carbon as a spacer and then another oxygen with a lone pair. It also has a single bond betwee...
by TJ Lai 2H
Mon Dec 07, 2020 8:51 pm
Forum: Administrative Questions and Class Announcements
Topic: Course Evaluations
Replies: 10
Views: 146

Re: Course Evaluations

Dr. Lavelle hasn't said anything about us getting points or extra credit for completing the UCLA course evaluations or the Sapling evaluation. What is the Sapling evaluation? I think this is referring to the survey about the Chemical Principles textbook that Dr. Lavelle sent in an email last Tuesday.
by TJ Lai 2H
Sun Dec 06, 2020 8:07 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Topic 9C Exercises Question 5
Replies: 7
Views: 87

Re: Topic 9C Exercises Question 5

You can usually tell if something is polydentate if the atom follows the structure Lone pair - spacer - spacer- lone pair. So for example in ox, it has an oxygen with a lone pair carbon as a spacer another carbon as a spacer and then another oxygen with a lone pair. It also has a single bond betwee...
by TJ Lai 2H
Wed Dec 02, 2020 9:26 am
Forum: Hybridization
Topic: Question 2F.15
Replies: 6
Views: 87

Re: Question 2F.15

Could someone explain under what circumstances the degree of contribution that a certain orbital (s, p, etc. would increase)? In other words, what would determine the degree of s-character?
by TJ Lai 2H
Wed Dec 02, 2020 8:13 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook Problem 2E #13
Replies: 3
Views: 62

Re: Textbook Problem 2E #13

Screenshot 2020-12-02 111221.png


I agree that there might be an issue with your textbook. Here's what the answer key looks like for that question for me.
by TJ Lai 2H
Wed Dec 02, 2020 8:04 am
Forum: Lewis Structures
Topic: Varying Arrangements of Structure
Replies: 5
Views: 63

Re: Varying Arrangements of Structure

For CH 2 Cl 2 there is no change in the VSEPR structure, but there is also no difference in the polarity of the molecule, right? Regardless of where the chlorine atoms are placed around the central carbon, the molecule has the same polarity. Is this correct? I believe so, yes. CH 2 Cl 2 has a tetra...
by TJ Lai 2H
Wed Dec 02, 2020 7:45 am
Forum: Hybridization
Topic: Textbook Q 2F #7
Replies: 4
Views: 57

Re: Textbook Q 2F #7

IMG_20201202_104500~2.jpg Here's how I drew the Lewis structure. The lone pair, as well as the bonding pairs, all "count" with regards to hybridization, so in this case AsF3 has 4 groups that count towards hybridization -> sp3 Here's a really quick and helpful video that I've used that ex...
by TJ Lai 2H
Sat Nov 28, 2020 8:05 pm
Forum: Octet Exceptions
Topic: Expanded Octet Question
Replies: 8
Views: 85

Re: Expanded Octet Question

^^^ I think Beryllium, Boron, Aluminum tend to have incomplete (not expanded) octets

this was a helpful resource for me: https://courses.lumenlearning.com/chemi ... ctet-rule/
by TJ Lai 2H
Sat Nov 28, 2020 7:59 pm
Forum: General Science Questions
Topic: Grade Breakdown
Replies: 35
Views: 382

Re: Grade Breakdown

I don't think he mentions anything on this, but he does say 50% or higher is required to pass with a C- or higher. I saw that too and was so confused... He is saying if you earn a 50% in the class you automatically pass? yep I think to pass the class with a C- or higher you'll need at least a 50% i...
by TJ Lai 2H
Sat Nov 28, 2020 7:52 pm
Forum: Administrative Questions and Class Announcements
Topic: 14B vs 14A
Replies: 12
Views: 169

Re: 14B vs 14A

I think 14B will be asynchronous, similar to 14A
by TJ Lai 2H
Sat Nov 28, 2020 7:48 pm
Forum: Administrative Questions and Class Announcements
Topic: Dr. Lavelle's Email
Replies: 3
Views: 62

Re: Dr. Lavelle's Email

I've emailed Dr. Lavelle before and he was very prompt at responding! So definitely try that if you're not able to attend / get his attention during office hours (I know there are often lots of other students there).
by TJ Lai 2H
Mon Nov 23, 2020 9:14 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Why are hydrogen bonds so strong relative to other dipole-dipole bonds?
Replies: 11
Views: 149

Re: Why are hydrogen bonds so strong relative to other dipole-dipole bonds?

Thanks for everyone's responses! I still don't really understand why hydrogen bonds are unique in that they are so much stronger relative to other dipole-dipole bonds (-20 kJ/mol vs. -2 kJ/mol). It doesn't totally make sense to me that hydrogen bonds are 10X stronger than other dipole-dipole bonds o...
by TJ Lai 2H
Sat Nov 21, 2020 4:29 pm
Forum: Formal Charge and Oxidation Numbers
Topic: chemical formula of compound
Replies: 6
Views: 71

Re: chemical formula of compound

Can someone explain aluminum hydride to me? I know the answer is AlH3, but I'm confused as to how the +3 ionic charge for aluminum balances the +1 ionic charge for hydrogen. Al has a charge of +3 and H has a charge +1, so in order to create the compound, you are basically just swapping the charges ...
by TJ Lai 2H
Sat Nov 21, 2020 4:28 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Why are hydrogen bonds so strong relative to other dipole-dipole bonds?
Replies: 11
Views: 149

Why are hydrogen bonds so strong relative to other dipole-dipole bonds?

Why are hydrogen bonds uniquely strong among dipole-dipole forces? For example, why are dipole-dipole bonds involving H so much stronger compared to dipole-dipole bonds involving an element that is even less electronegative, such as Si, or approximately the same electronegativity, such as P? Also, w...
by TJ Lai 2H
Sat Nov 21, 2020 3:35 pm
Forum: Administrative Questions and Class Announcements
Topic: 14B and 14BL
Replies: 13
Views: 172

Re: 14B and 14BL

Does anyone have an idea of what 14BL will be like over Zoom?
by TJ Lai 2H
Thu Nov 19, 2020 11:13 am
Forum: Formal Charge and Oxidation Numbers
Topic: chemical formula of compound
Replies: 6
Views: 71

Re: chemical formula of compound

Can someone explain aluminum hydride to me? I know the answer is AlH3, but I'm confused as to how the +3 ionic charge for aluminum balances the +1 ionic charge for hydrogen.
by TJ Lai 2H
Tue Nov 17, 2020 6:04 pm
Forum: Ionic & Covalent Bonds
Topic: Ionization energy
Replies: 4
Views: 845

Re: Ionization energy

Following the logic that Na becomes very stable after losing 1 electron as it attains noble gas configuration, can we also say that Na has higher 2nd ionization energy relative to Al?
by TJ Lai 2H
Sat Nov 14, 2020 2:30 pm
Forum: Dipole Moments
Topic: Sapling #19
Replies: 12
Views: 86

Re: Sapling #19

I just saw that Dr. Lavelle responded to another post about this and said that H2S was a mistake (meant to say SO2).
by TJ Lai 2H
Sat Nov 14, 2020 2:21 pm
Forum: Dipole Moments
Topic: Sapling #17
Replies: 7
Views: 159

Re: Sapling #17

FionaHunter21 wrote:Are london dispersion forces present in all nonpolar molecules?


London dispersion forces are present in all molecules, but they are the only intermolecular force present in nonpolar molecues.
by TJ Lai 2H
Sat Nov 14, 2020 2:19 pm
Forum: Dipole Moments
Topic: Week 5/6 Sapling Question
Replies: 4
Views: 111

Re: Week 5/6 Sapling Question

Each of the (slightly positive) H atoms can form a hydrogen bond with the slightly negative charge in the O atom of an H2O molecule. +4 hydrogen bonds Likewise, each of the (slightly negative) N atoms can form a hydrogen bond with the slightly negative positive charge in the H atom of an H2O molecul...
by TJ Lai 2H
Sat Nov 14, 2020 1:45 pm
Forum: Dipole Moments
Topic: Sapling Question #13
Replies: 5
Views: 56

Re: Sapling Question #13

So other hydrogen atoms can form hydrogen bonds to any N,O, or F molecule that has unpaired electrons in the valence shell? Or do they need to be N,O, and F atoms that are already bonded with a hydrogen? The way I understand it, the hydrogen atom must be covalently bonded to an electronegative atom...
by TJ Lai 2H
Sat Nov 14, 2020 1:38 pm
Forum: Dipole Moments
Topic: Sapling #19
Replies: 12
Views: 86

Re: Sapling #19

I said dipole-dipole, because O is more electronegative than S and the partially positive (S) and partially negative (O) areas of each molecule are attracted to each other. Not sure why it says H2S or that H2S is polar (I think it meant to say SO2).
by TJ Lai 2H
Sun Nov 08, 2020 3:24 pm
Forum: Administrative Questions and Class Announcements
Topic: Posting Screenshots on Chem Community
Replies: 3
Views: 32

Re: Posting Screenshots on Chem Community

Screenshot 2020-11-08 182308.png


I just tried it, and basically I saved the screenshot, dragged it into the textbox, and then at the bottom where it says "Attachments," I clicked "place inline."
by TJ Lai 2H
Sun Nov 08, 2020 3:20 pm
Forum: Administrative Questions and Class Announcements
Topic: Question for Students about High School Chem
Replies: 25
Views: 122

Re: Question for Students about High School Chem

I really, really appreciate that Dr. Lavelle starts every section off with fundamentals! I never took AP Chem and retained essentially zero chemistry from high school, but I've found this class to still be pretty manageable even with basically no chem background.
by TJ Lai 2H
Sun Nov 08, 2020 3:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14B Enrollment
Replies: 27
Views: 350

Re: Chem 14B Enrollment

BoparaiAdeshsurjit2I wrote:Will Chem 14B also have asynchronous lectures?


I think it will, just like 14A
by TJ Lai 2H
Sun Nov 08, 2020 3:13 pm
Forum: Administrative Questions and Class Announcements
Topic: Taking Bio and Chem simultaneously
Replies: 26
Views: 114

Re: Taking Bio and Chem simultaneously

I'm taking the LS7A along with Chem14A right now. It's not too bad of a combination, but I've found LS7A to be more time-consuming than Chem (it takes me longer to memorize/understand the concepts). I retained basically zero information from high school biology and chemistry though, so if you still ...
by TJ Lai 2H
Sun Nov 08, 2020 3:08 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14BL?
Replies: 7
Views: 57

Re: Chem 14BL?

Does anyone know what BL looks like as an online class? Will there be lab demonstrations over Zoom?
by TJ Lai 2H
Sat Oct 31, 2020 2:22 pm
Forum: Administrative Questions and Class Announcements
Topic: Chemistry Modules
Replies: 7
Views: 60

Re: Chemistry Modules

I found them to be super helpful too, so I'm kinda sad that there won't be more modules for the rest of the material (but totally understandable given how much work is put into running the class already). Hopefully for future years Dr. Lavelle can use the class recordings from this quarter!
by TJ Lai 2H
Sat Oct 31, 2020 2:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Scores
Replies: 4
Views: 63

Re: Midterm Scores

I think Dr. Lavelle said that one of the midterm questions had an error so they will have to go through each midterm individually, which will take some time.
by TJ Lai 2H
Fri Oct 30, 2020 7:11 am
Forum: Significant Figures
Topic: Sig Figs for electron shells
Replies: 4
Views: 73

Sig Figs for electron shells

For electron shells, can we assume that each quantity has "infinite" sig figs (e.g. 2.000000...) because we know that shells can only be whole numbers? So in a problem, we should base the number of sig figs off of the value we are given for the wavelength/ frequency etc.?
by TJ Lai 2H
Thu Oct 29, 2020 9:36 am
Forum: Molarity, Solutions, Dilutions
Topic: Fundamentals G21
Replies: 3
Views: 50

Fundamentals G21

Hi everyone, G21 asks us to find the molarity of potassium and sulfide ions in a solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K2S, and 0.500 g of K3PO4 in 500 mL of water. I know the molarity equation is (moles of solute) / (volume of solution). For this problem, shouldn't the volum...
by TJ Lai 2H
Thu Oct 29, 2020 5:55 am
Forum: Administrative Questions and Class Announcements
Topic: Sapling Access Code
Replies: 5
Views: 62

Re: Sapling Access Code

I would send another email to the UCLA store, or call them if possible. Be persistent and I'm sure it will be fine :)
by TJ Lai 2H
Sun Oct 25, 2020 9:09 am
Forum: Properties of Light
Topic: Emission/Absorption
Replies: 6
Views: 83

Re: Emission/Absorption

I think for frequency and wavelength, we basically take the absolute values of the result because we know that frequency and wavelength can never be negative. I agree with Aaron that n1 and n2 should be thought of as n_final and n_initial (not just that the lower value has to be n1 and the higher va...
by TJ Lai 2H
Sun Oct 25, 2020 8:48 am
Forum: Administrative Questions and Class Announcements
Topic: Schrodingers/Orbitals on Midterm?
Replies: 2
Views: 32

Re: Schrodingers/Orbitals on Midterm?

I think the main thing to know is that, conceptually, we can solve for the wavefunction using Schrodinger's equation and the square of the wavefunction is proportional to the probability density for where a particle could be in a region.
by TJ Lai 2H
Sun Oct 25, 2020 8:42 am
Forum: Administrative Questions and Class Announcements
Topic: Printouts for Midterm
Replies: 8
Views: 71

Re: Printouts for Midterm

Here are the printouts Dr. Lavelle provided:

Periodic table:
https://lavelle.chem.ucla.edu/wp-conten ... _IUPAC.pdf

Equations and constants:
https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf
by TJ Lai 2H
Sat Oct 24, 2020 8:10 am
Forum: Administrative Questions and Class Announcements
Topic: Memorize electromagnetic spectrum for midterm?
Replies: 7
Views: 44

Memorize electromagnetic spectrum for midterm?

Does anyone know if we should memorize the electromagnetic spectrum for the midterm? For example, now that visible light has wavelengths between 400 and 700 nm, etc. Thanks!
by TJ Lai 2H
Sat Oct 24, 2020 8:00 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post Mod Q
Replies: 3
Views: 46

Re: Atomic Spectra Post Mod Q

I was torn between the choices, "Yes, because each molecule has a unique spectral pattern or fingerprint" and "Yes, because most molecule have a common spectral pattern or fingerprint." Is it the case that every molecule has a unique spectral fingerprint? Or can molecular spectro...
by TJ Lai 2H
Sun Oct 18, 2020 6:54 pm
Forum: Photoelectric Effect
Topic: Textbook Question 1A.11
Replies: 3
Views: 51

Re: Textbook Question 1A.11

Also, the Balmer and Lyman series refer to different "types" of spectral lines (Balmer series refers to spectral lines for visible light, Lyman series for UV)
by TJ Lai 2H
Sun Oct 18, 2020 6:42 pm
Forum: Properties of Electrons
Topic: Electron Wave-Particle Duality
Replies: 10
Views: 117

Re: Electron Wave-Particle Duality

Adam, here's a diagram that captures wavelength vs. frequency vs. amplitude.
7e66c3308d3bf56acd075312fb84143b.jpg


The energy of each photon is equal to the Planck's constant * frequency
by TJ Lai 2H
Sun Oct 18, 2020 6:25 pm
Forum: Properties of Light
Topic: Sapling homework question 5
Replies: 3
Views: 45

Re: Sapling homework question 5

First, I calculated frequency using the equation c = Wavelength * Frequency Remember that c is a constant equal to 3.00 * 10^8 m/s and the wavelength is given as 9.23×10−4 cm After solving for the frequency, plug that into the equation E = h * Frequency to solve for the Energy per photon Remember th...
by TJ Lai 2H
Sun Oct 18, 2020 6:13 pm
Forum: Properties of Light
Topic: Study Advice
Replies: 50
Views: 308

Re: Study Advice

I've found doing the optional book problems to be really helpful for me in terms of understanding the material. I like that the Answer Key goes through each question very clearly and systematically.
by TJ Lai 2H
Sun Oct 18, 2020 6:10 pm
Forum: Administrative Questions and Class Announcements
Topic: UCLA Store Updates on Ebook/Sapling access card
Replies: 16
Views: 150

Re: UCLA Store Updates on Ebook/Sapling access card

I ordered mine 3 weeks ago or so but never received it in the mail. However, I did get an email from textonline@asucla.ucla.edu with my code (I never requested it, they somehow just knew to email it to me)...
by TJ Lai 2H
Fri Oct 09, 2020 7:39 pm
Forum: Administrative Questions and Class Announcements
Topic: Turning in textbook problems
Replies: 10
Views: 134

Re: Turning in textbook problems

I would definitely do some textbook problems (even if they're not graded for credit) as the prof. says that some of the questions from the exams will be taken from the textbook.
by TJ Lai 2H
Fri Oct 09, 2020 7:28 pm
Forum: Limiting Reactant Calculations
Topic: Sapling HW Week 1 Q10
Replies: 4
Views: 96

Re: Sapling HW Week 1 Q10

I was also confused about what happens to the Br and Mg. I just assumed that they weren't shown in the product because they weren't important to the question, but that the final product actually looks something like C7H16O + MgBr (which I'm pretty sure isn't an actual compound, so maybe equation in ...
by TJ Lai 2H
Fri Oct 09, 2020 7:10 pm
Forum: Administrative Questions and Class Announcements
Topic: Exam Regulations
Replies: 7
Views: 65

Re: Exam Regulations

I'm pretty sure it will be closed book/ notes. We will also be installing Respondus which (I believe) monitors your browser activity during the exam.
by TJ Lai 2H
Fri Oct 09, 2020 7:06 pm
Forum: Limiting Reactant Calculations
Topic: Week 1 Sapling Q. 10
Replies: 5
Views: 116

Re: Week 1 Sapling Q. 10

Here's a picture of how I determined the molecular formulas based off of the diagrams

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