Search found 105 matches

by Mary Gallo 1G
Sun Feb 28, 2021 2:33 pm
Forum: Balancing Redox Reactions
Topic: Sapling W7/W8 #4
Replies: 6
Views: 31

Re: Sapling W7/W8 #4

Thank you, Shannon! I really appreciate it.
by Mary Gallo 1G
Sun Feb 28, 2021 1:56 pm
Forum: Balancing Redox Reactions
Topic: Sapling W7/W8 #4
Replies: 6
Views: 31

Sapling W7/W8 #4

Hi! I am having trouble finding the half-reactions for this problem:
The unbalanced equation for the reaction of gold with aqua regia is given. Add the stoichiometric coefficients to the equation to balance it.
Au(s) + HNO3(aq) + HCl(aq) --> HAuCl4(aq) + NO2(g) + H2O(l)

Thank you!
by Mary Gallo 1G
Sun Feb 28, 2021 1:27 pm
Forum: Student Social/Study Group
Topic: Points needed to pass?
Replies: 64
Views: 215

Re: Points needed to pass?

A C-, or minimum passing grade, in this class would be receiving 200/400 points.
by Mary Gallo 1G
Sun Feb 28, 2021 1:26 pm
Forum: Balancing Redox Reactions
Topic: Week 7/8 #3
Replies: 8
Views: 60

Re: Week 7/8 #3

I was having trouble with this problem and your walkthrough was super helpful! Thank you so much.
by Mary Gallo 1G
Sun Feb 21, 2021 5:28 pm
Forum: Calculating Work of Expansion
Topic: Work sign
Replies: 37
Views: 75

Re: Work sign

Work done by the system is negative and work done on the system is positive. When a system does work, it is losing energy, thus the sign is negative. When work is being done on the system there is energy being transferred to it, making the work of the system positive.
by Mary Gallo 1G
Sun Feb 21, 2021 5:26 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open vs closed
Replies: 24
Views: 66

Re: Open vs closed

Open systems allow both energy and matter to be exchanged with the surroundings. Closed systems only allow energy transfer with the surroundings. Finally, isolated systems do not allow anything to be transferred with the surroundings.
by Mary Gallo 1G
Sun Feb 21, 2021 5:25 pm
Forum: Student Social/Study Group
Topic: Post Midterm 2 De-stressing
Replies: 90
Views: 240

Re: Post Midterm 2 De-stressing

I am a self-proclaimed "stress baker", so I decided to bake some chocolate cookies this weekend. Baking takes my mind off of challenging academics and always comes with a tasty reward! :)
by Mary Gallo 1G
Sun Feb 21, 2021 5:23 pm
Forum: Administrative Questions and Class Announcements
Topic: Sapling Assignments
Replies: 28
Views: 154

Re: Sapling Assignments

Those modules are optional for the course. They teach you how to use certain tools in Sapling when answering homework questions.
by Mary Gallo 1G
Sun Feb 21, 2021 5:19 pm
Forum: General Science Questions
Topic: Grades
Replies: 30
Views: 388

Re: Grades

You can either view your grades on the Grades tab of CCLE or go to MyUCLA.
by Mary Gallo 1G
Sun Feb 14, 2021 9:53 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2
Replies: 31
Views: 142

Re: Midterm 2

Midterm 2 will cover Outline 3 and Outline 4, but Outline 3 will only include topics that were not on Midterm 1 (so no ways of calculating reaction enthalpies).
by Mary Gallo 1G
Sun Feb 14, 2021 9:50 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: sapling #18
Replies: 3
Views: 26

Re: sapling #18

First you will need to find ∆G of the reaction, where ∆G = sum∆G(products) - sum∆G(reactants) (Make sure if you multiply the ∆G of each molecule by the amount of moles of it there are in the reaction when summing them.) Next you will use the equation: ∆G= - RT ln(K) Which can be arranged as: K=e^(-∆...
by Mary Gallo 1G
Sun Feb 14, 2021 7:21 pm
Forum: Student Social/Study Group
Topic: Finals
Replies: 23
Views: 64

Re: Finals

I agree with others as I found the final significantly harder than the midterms. I prepared the same way for both types of exams (except a lot more for the final), but it was still very challenging. I think I will spend more time practicing questions from the textbook this quarter.
by Mary Gallo 1G
Sun Feb 14, 2021 7:18 pm
Forum: Administrative Questions and Class Announcements
Topic: Can We Review our Exams?
Replies: 69
Views: 245

Re: Can We Review our Exams?

You can go to your TA's Office Hours to review your midterm!
by Mary Gallo 1G
Sun Feb 14, 2021 7:16 pm
Forum: Administrative Questions and Class Announcements
Topic: struggling
Replies: 73
Views: 260

Re: struggling

I find that when I am struggling with certain topics in this class, the UA sessions always help me understand them better. If you need help conceptually I suggest the Step-Up sessions and if you're looking for practice problems I would go to the Workshops!
by Mary Gallo 1G
Tue Feb 02, 2021 8:53 pm
Forum: Calculating Work of Expansion
Topic: Sapling #14 Weeks 3 and 4
Replies: 6
Views: 69

Re: Sapling #14 Weeks 3 and 4

Nevermind, I redid all my calculations and got the correct answer. Not sure where I slipped up but thank you so much for the help!
by Mary Gallo 1G
Tue Feb 02, 2021 8:30 pm
Forum: Calculating Work of Expansion
Topic: Sapling #14 Weeks 3 and 4
Replies: 6
Views: 69

Re: Sapling #14 Weeks 3 and 4

Hi! So for the first step, the volume remains constant so there is 0 work being done. In the second step you could use the w=-(Pexternal)(deltaV). Your answer will come out with the units of L x atm, so you want to convert that into Joules. Then since the work from the first step was 0, your total ...
by Mary Gallo 1G
Tue Feb 02, 2021 1:17 pm
Forum: Calculating Work of Expansion
Topic: Sapling #14 Weeks 3 and 4
Replies: 6
Views: 69

Re: Sapling #14 Weeks 3 and 4

Hi! So for the first step, the volume remains constant so there is 0 work being done. In the second step you could use the w=-(Pexternal)(deltaV). Your answer will come out with the units of L x atm, so you want to convert that into Joules. Then since the work from the first step was 0, your total ...
by Mary Gallo 1G
Tue Feb 02, 2021 1:00 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Week 3/4 Sapling #12
Replies: 2
Views: 27

Re: Week 3/4 Sapling #12

Thank you so much for the help!
by Mary Gallo 1G
Tue Feb 02, 2021 12:34 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Week 3/4 Sapling #12
Replies: 2
Views: 27

Week 3/4 Sapling #12

Hi! I am unsure how to go about solving question #12 from the Sapling homework. What equations should we use to solve this? Part a: At constant volume, the heat of combustion of a particular compound, compound A, is −3761.0 kJ/mol. When 1.527 g of compound A (molar mass=120.79 g/mol) is burned in a ...
by Mary Gallo 1G
Tue Feb 02, 2021 12:30 pm
Forum: Calculating Work of Expansion
Topic: different R constants
Replies: 7
Views: 23

Re: different R constants

In addition to everyone else, I think it is helpful to write down the units of each thing in your calculations. This ensures not only that you choose the correct R value, but that your answer is also solved in the right units.
by Mary Gallo 1G
Tue Feb 02, 2021 12:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Week 3/4 Sapling #9
Replies: 13
Views: 118

Week 3/4 Sapling #9

If you combine 230.0 mL of water at 25.00 C and 100.0 mL of water at 95.00 C, what is the final temperature of the mixture? Use 1.00 g/mL as the density of water.

What equation should we be using to solve this problem?
Thank you!
by Mary Gallo 1G
Fri Jan 29, 2021 3:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook question 4E.9
Replies: 8
Views: 56

Re: Textbook question 4E.9

I had the same issue with this problem, thank you! Could someone please explain what Kekule structures are? I wanted to make a post about this but I thought it would be helpful to add it onto this thread. Hi! Kekule structures were the original structures proposed for the structure of benzene. This...
by Mary Gallo 1G
Thu Jan 28, 2021 11:14 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook question 4E.9
Replies: 8
Views: 56

Re: Textbook question 4E.9

Thank you for the guidance! A follow up question- So to "calculate the lowering in molar energy" would we do the delta H of the structure with resonance subtracted by the delta H of the structure without resonance? I got 3108-2880 = 228 Is this correct? Does it mean that there is a 228 kJ...
by Mary Gallo 1G
Tue Jan 26, 2021 8:01 pm
Forum: Administrative Questions and Class Announcements
Topic: Questions on Midterm 1
Replies: 7
Views: 82

Re: Questions on Midterm 1

Dr. Lavelle just sent an email saying there will be 12-14 questions on the midterm.
For more information about the midterm you can look here:
https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Chem14B_Midterm1.pdf
Hope this helps!
by Mary Gallo 1G
Mon Jan 25, 2021 9:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook question 4E.9
Replies: 8
Views: 56

Re: Textbook question 4E.9

Hi! In a benzene structure without resonance, there would be 3 C-C double bonds and 3 C-C single bonds. For the benzene structure with resonance, there are 6 resonance-stabilized bonds. So for this problem you are calculating the difference in energy between the two types of benzene structures. You ...
by Mary Gallo 1G
Mon Jan 25, 2021 9:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook 4D.23
Replies: 3
Views: 41

Re: Textbook 4D.23

Thank you so much! I wasn't sure how to solve the last bit, your explanation really helped!
by Mary Gallo 1G
Mon Jan 25, 2021 7:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook 4D.23
Replies: 3
Views: 41

Textbook 4D.23

Hi! I am having trouble understanding how to do problem 4D.23 from the textbook: Calculate the standard enthalpy of formation of dinitrogen pentoxide from the following data: 2NO(g)+O2(g) --> 2NO2(g) ∆H = +498.4 kJ 4NO2(g)+O2(g) --> 2N2O5(g) ∆H = -110.2 kJ and the from the standard enthalpy of forma...
by Mary Gallo 1G
Wed Jan 20, 2021 3:21 pm
Forum: Phase Changes & Related Calculations
Topic: Phase change and temperature
Replies: 6
Views: 19

Re: Phase change and temperature

Hi! To further clarify, when steam (vapor) touches the skin, it goes through the phase change of condensation, which is an exothermic reaction (the opposite of vaporization). When a reaction is exothermic, ∆H is a negative value. This release of energy goes into the skin all at once during the phase...
by Mary Gallo 1G
Tue Jan 19, 2021 4:30 pm
Forum: Phase Changes & Related Calculations
Topic: Usage of Ph with acids and bases
Replies: 6
Views: 27

Re: Usage of Ph with acids and bases

To add on, pH tells us how acidic or basic a solution is. A solution that has a low pH is more acidic , and this is due to a higher concentration of H30+ ions. A solution that has a high pH is more basic due to a higher concentration of OH- ions. When we take the negative log of the H30+ concentrati...
by Mary Gallo 1G
Tue Jan 19, 2021 4:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Moles vs Concentrations in ICE Box
Replies: 21
Views: 75

Re: Moles vs Concentrations in ICE Box

I would suggest using concentrations in ICE boxes because we use concentrations when working with K values, pH and pOH, or compositions of solutions.
by Mary Gallo 1G
Mon Jan 18, 2021 11:37 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.15
Replies: 2
Views: 22

Re: Textbook 6D.15

Thank you so much for the help!
by Mary Gallo 1G
Mon Jan 18, 2021 10:58 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.15
Replies: 2
Views: 22

Textbook 6D.15

Calculate the pH of (a) 0.19M NH4Cl(aq); (b) 0.055M AlCl3(aq). I understand how to solve part a, but I am struggling with part b. I am not sure how we get the dissociation equation shown in the solutions manual as well as where the Ka value comes from. I would appreciate some help with this problem,...
by Mary Gallo 1G
Thu Jan 14, 2021 11:02 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Sapling Homework 2, Questions 9 and 10
Replies: 2
Views: 46

Re: Sapling Homework 2, Questions 9 and 10

Hi! Although these images come from the solution pages of these two problems, I find them really helpful in understanding these problems conceptually: Screen Shot 2021-01-14 at 10.55.08 AM.png For acidic solutions, the diagram is saying that when the pH is less than the pKa the solution is neutral b...
by Mary Gallo 1G
Wed Jan 13, 2021 10:42 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Sapling Week 2 #5
Replies: 4
Views: 68

Re: Sapling Week 2 #5

Hi! Could someone explain why we calculate [BH+]/([BH+][B]) instead [BH+]/[B] for the last step? I'm trying to understand it conceptually. Thank you!
by Mary Gallo 1G
Wed Jan 13, 2021 8:27 pm
Forum: Administrative Questions and Class Announcements
Topic: Class on 1/18/21 Holiday
Replies: 9
Views: 68

Re: Class on 1/18/21 Holiday

Hi! Dr. Lavelle just sent an email saying there will be no class this Monday.
by Mary Gallo 1G
Wed Jan 13, 2021 7:32 pm
Forum: General Science Questions
Topic: Rusty on High School Chem [ENDORSED]
Replies: 219
Views: 143049

Re: Rusty on High School Chem [ENDORSED]

Hi! I had very little background in chemistry when I started 14A with Dr. Lavelle last quarter. I was nervous about falling behind, but Dr. Lavelle always made sure to go over the basics/review fundamentals in lectures. Initially I was not utilizing the UA Sessions for extra help. However, I would h...
by Mary Gallo 1G
Wed Jan 13, 2021 7:27 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5I.27
Replies: 6
Views: 43

Re: 5I.27

When Q<K, this means that there is a greater concentration of reactants than there would be at equilibrium. Therefore, the reaction would actually proceed right, towards the products, to achieve equilibrium.
by Mary Gallo 1G
Mon Jan 11, 2021 12:07 pm
Forum: Student Social/Study Group
Topic: Study Tips
Replies: 32
Views: 112

Re: Study Tips

I find that completing practice problems is the best way for the material to stick. They require you to do critical thinking, but eventually the problems become almost mechanic. I would suggest doing all of the textbook problems from the outlines, as they best reflect test material. If you still wan...
by Mary Gallo 1G
Fri Jan 08, 2021 12:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Picking answer from quadratic solutions
Replies: 12
Views: 69

Re: Picking answer from quadratic solutions

Hi! To add on, you would not want to pick a value for x that is greater than your initial concentrations because when you factor this in to find the concentrations at equilibrium, you would get a negative value. A negative concentration value would not make sense for the problem, so always choose th...
by Mary Gallo 1G
Fri Jan 08, 2021 12:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: sapling week 1 #9
Replies: 15
Views: 209

Re: sapling week 1 #9

Hello! I am also having difficulty with this question. I understand how to find x, but where do I factor in the new concentration of NO given in the problem (0.800 for my problem)? The feedback just says to determine the effect of adding NO and go from there, but I am unsure how to do this mathemat...
by Mary Gallo 1G
Fri Jan 08, 2021 12:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Lecture 3 PCl5 Example Question
Replies: 2
Views: 22

Re: Lecture 3 PCl5 Example Question

I believe we are using concentrations because of the information we were given in this problem. Since we were given Kc in the problem, and not Kp, we do not have enough information to find the composition of the equilibrium mixture using partial pressures. Instead, we must use the given moles of PCl...
by Mary Gallo 1G
Fri Jan 08, 2021 12:39 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic and Endothermic
Replies: 4
Views: 53

Re: Exothermic and Endothermic

I find that using visuals, similar to the ones Dr. Lavelle drew in lecture today, helps me understand this concept. For an endothermic reaction (where heat is absorbed) the ∆H is positive: Screen Shot 2021-01-08 at 12.38.07 PM.png Since a reaction favors the thing with the greatest enthalpy (H), hea...
by Mary Gallo 1G
Tue Jan 05, 2021 10:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc favoring products
Replies: 10
Views: 100

Re: Kc favoring products

When K>1 then the chemical reaction will favor the products. However, K needs to be greater than 10^3 to strongly favor the products.

The reverse goes for K<1, where the chemical reaction favors the reactants. In this case, K needs to be less than 10^-3 to strongly favor the reactants.
by Mary Gallo 1G
Tue Jan 05, 2021 12:02 pm
Forum: Student Social/Study Group
Topic: Advice for someone who didn't take 14A with professor Lavelle
Replies: 61
Views: 338

Re: Advice for someone who didn't take 14A with professor Lavelle

The most helpful things for me in 14A were doing the textbook problems. They were often similar to questions that would appear on exams so it made for good practice. I also would recommend going to UA sessions for extra help whenever you have the time. Step-Up sessions are useful if you need a littl...
by Mary Gallo 1G
Tue Dec 08, 2020 6:38 pm
Forum: Molarity, Solutions, Dilutions
Topic: Textbook Fundamentals G #13
Replies: 1
Views: 39

Re: Textbook Fundamentals G #13

To solve this problem you are going to use formula: M1V1=M2V2. Your M1 is 0.20M and your V1 is 1.0L (as given in problem). Since 3.0L of water is added, your V2 will be 4.0L (1.0L+3.0L). Now you can solve for the final molarity value. To convert the molarity into moles you use the formula: M=mol/L T...
by Mary Gallo 1G
Tue Dec 08, 2020 4:13 pm
Forum: Polyprotic Acids & Bases
Topic: Proton vs H+
Replies: 14
Views: 141

Re: Proton vs H+

A neutral H atom has 1 proton and 1 electron. When it is ionized to become H+ the electron is lost so there is just 1 proton remaining. Therefore, the H+ ion can be referred to as a proton.
by Mary Gallo 1G
Tue Dec 08, 2020 4:10 pm
Forum: Significant Figures
Topic: Things to remember for final?
Replies: 20
Views: 159

Re: Things to remember for final?

Is there some kind of sheet or something in the textbook that lists all of the strong acids/bases we should know for the final?
by Mary Gallo 1G
Tue Dec 08, 2020 4:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Square Planar vs. Tetrahedral
Replies: 15
Views: 134

Re: Square Planar vs. Tetrahedral

Octahedral involves 6 bonded atoms attached to the central atom (AX6). Tetrahedral involves 4 bonded atoms attached to the central atom (AX4). Square Planar involves 4 bonded atoms and 2 lone pairs attached to the central atom (AX4E2). While both tetrahedral and square planar have 4 bonded atoms, sq...
by Mary Gallo 1G
Tue Dec 08, 2020 3:59 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted vs Lewis
Replies: 8
Views: 59

Re: Bronsted vs Lewis

An acid will accept an electron (Lewis acid) / donate a proton (Bronstead acid). A base will donate an electron (Lewis base) / accept a proton (Bronstead base). So Lewis' discusses electrons and Bronsteads refer to protons. They are just two different ways of thinking about what will happen to a mol...
by Mary Gallo 1G
Fri Dec 04, 2020 11:00 pm
Forum: Bronsted Acids & Bases
Topic: Textbok Problem J.1
Replies: 4
Views: 51

Re: Textbok Problem J.1

Bronstead acids will donate protons and Bronstead bases will accept protons. I think that drawing the Lewis structure can be helpful to visualize what will happen (lone pairs, H+, OH-). Another thing to look out for that hasn't been mentioned is that OH- often indicates a Bronstead base because it i...
by Mary Gallo 1G
Fri Dec 04, 2020 10:42 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Dentates
Replies: 3
Views: 56

Re: Dentates

Thank you both so much for the help! I really appreciate it.
by Mary Gallo 1G
Tue Dec 01, 2020 1:29 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Dentates
Replies: 3
Views: 56

Dentates

Are dentates just used to determine the coordination number of a compound? Also, what is a good way to determine if a dentate is mono, bi, tri, etc?
by Mary Gallo 1G
Tue Dec 01, 2020 1:26 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Lewis acids and bases
Replies: 22
Views: 134

Re: Lewis acids and bases

Lewis acids accept electrons while lewis bases donate electrons. The acids will usually have a positive charge and want electrons to neutralize the charge. Lewis bases will usually be negatively charged and willing to donate the extra electrons.
by Mary Gallo 1G
Tue Dec 01, 2020 1:23 pm
Forum: Bond Lengths & Energies
Topic: Higher Melting Point
Replies: 27
Views: 261

Re: Higher Melting Point

CHI3 is larger than CHF3 and therefore has stronger London Dispersion forces. There is more energy required to dissociate the atoms in CHI3 so its melting point is higher.
by Mary Gallo 1G
Fri Nov 27, 2020 2:38 pm
Forum: Biological Examples
Topic: Examples of Square Planar Molecules?
Replies: 7
Views: 81

Re: Examples of Square Planar Molecules?

One common square planar molecule is XeF4 (we saw this molecule in lecture). Due to the geometry of this molecule, the polar covalent bonds have dipoles that cancel (equal and opposite directions) and the electron lone pairs are on opposite sides of the central atom. This means that all charges canc...
by Mary Gallo 1G
Fri Nov 27, 2020 2:30 pm
Forum: Hybridization
Topic: 2sp^2 vs 3sp^2
Replies: 6
Views: 47

Re: 2sp^2 vs 3sp^2

Yes! Hybridization correlates to the energy level of the atom's orbital that has hybridized electron(s).
by Mary Gallo 1G
Fri Nov 27, 2020 2:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: What does delocalized π bond mean?
Replies: 18
Views: 150

Re: What does delocalized π bond mean?

Delocalized pi bonds refer to molecules that have resonance structures. This means that the pi bond can be between different atoms in the same molecule as long as it has resonance.
by Mary Gallo 1G
Fri Nov 27, 2020 2:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape Names
Replies: 50
Views: 311

Re: Shape Names

Yes, when there are 4 regions of electron density and 2 are bonding then the VSEPR shape can be referred to as bent or angular.
by Mary Gallo 1G
Fri Nov 27, 2020 2:23 pm
Forum: Student Social/Study Group
Topic: Final Exam Tips
Replies: 24
Views: 146

Re: Final Exam Tips

I think I am going to review textbook and Sapling homework problems to review for the final. I also want to attend more UA sessions.
by Mary Gallo 1G
Fri Nov 20, 2020 11:08 pm
Forum: Student Social/Study Group
Topic: Study Tips for Final Exam
Replies: 57
Views: 451

Re: Study Tips for Final Exam

I think that reviewing the textbook and Sapling hw problems from each section will be helpful in preparing for the final. This way you can focus on what questions you get wrong and rewatch lectures or read through any notes. I also want to take more advantage of the workshops we have available to us...
by Mary Gallo 1G
Thu Nov 19, 2020 1:23 pm
Forum: Dipole Moments
Topic: Dipole Moments 3F.13
Replies: 1
Views: 22

Dipole Moments 3F.13

In question 3F.13 in the textbook we are asked to choose the formation of CH2Cl2 atoms that would create the strongest bonds. I understand alignment II is correct because there are more dipole-dipole bonds where the negative dipole of Cl connects to the positive dipole of H. However, I was wondering...
by Mary Gallo 1G
Wed Nov 18, 2020 5:23 pm
Forum: Student Social/Study Group
Topic: Midterm 2
Replies: 19
Views: 191

Re: Midterm 2

I really like doing the textbook problems to study for midterms. It is also nice to have the solutions in the back of the book so I can focus on certain topics if I am not getting those questions correct.
by Mary Gallo 1G
Wed Nov 18, 2020 5:20 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability and Polarizing Power
Replies: 7
Views: 90

Re: Polarizability and Polarizing Power

Wow, I really like the balloon and dart analogy! Thank you both for the explanations, they really help!
by Mary Gallo 1G
Wed Nov 18, 2020 5:18 pm
Forum: General Science Questions
Topic: Which would have lower ionization energy?
Replies: 13
Views: 125

Re: Which would have lower ionization energy?

Chlorine has a lower ionization energy than oxygen because it is easier to remove an electron from a higher orbital. To ionize chlorine an electron is removed from 3p subshell, which is higher in energy than the electron, from the 2p subshell, that would be removed from oxygen. Chlorine also has ano...
by Mary Gallo 1G
Mon Nov 16, 2020 4:06 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Aufbau Order
Replies: 5
Views: 31

Re: Aufbau Order

Dr. Lavelle prefers that we write the 3d subshell before the 4s subshell because once the 3d subshells starts filling it is lower in energy than 4s. This order of writing is also helpful if you are starting with the ground state electron configuration and finding the configuration for a cation. You ...
by Mary Gallo 1G
Mon Nov 16, 2020 4:01 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability and Polarizing Power
Replies: 7
Views: 90

Polarizability and Polarizing Power

Hi! Does anyone have a good way to remember what makes an atom/ion more polarizable and which atoms/ions have more polarizing power? I'm having a little trouble with those concepts.
by Mary Gallo 1G
Tue Nov 10, 2020 3:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling HW Q17
Replies: 5
Views: 55

Sapling HW Q17

Question 17 of the W5/W6 Sapling homework asks: Which molecules exhibit only London (dispersion) forces? I understand how to determine that if a molecule is fully nonpolar it exhibits only London dispersion forces. However, with the other molecules, a knowledge of molecular structure is required to ...
by Mary Gallo 1G
Tue Nov 10, 2020 3:36 pm
Forum: Electronegativity
Topic: Sapling HW Q13
Replies: 3
Views: 29

Re: Sapling HW Q13

Thank you so much Crystal, this helped a ton! I really appreciate the picture too. :)
by Mary Gallo 1G
Tue Nov 10, 2020 3:00 pm
Forum: Electronegativity
Topic: Sapling HW Q13
Replies: 3
Views: 29

Sapling HW Q13

From Sapling HW Question 13: Urea is an organic compound widely used as a fertilizer. Its solubility in water allows it to be made into aqueous fertilizer solutions and applied to crops in a spray. What is the maximum theoretical number of water molecules that one urea molecule can hydrogen bond wit...
by Mary Gallo 1G
Tue Nov 10, 2020 2:45 pm
Forum: Ionic & Covalent Bonds
Topic: Size of Bonds
Replies: 28
Views: 104

Re: Size of Bonds

There are more electrons shared between atoms in a double bond. Therefore, the attractive forces between atoms with double bonds are stronger, thus pulling them in closer. Atoms that share a single bond have smaller attractive forces in comparison, and are usually longer.
by Mary Gallo 1G
Tue Nov 10, 2020 2:43 pm
Forum: Lewis Structures
Topic: Sapling week 5/6 Question 3
Replies: 5
Views: 57

Re: Sapling week 5/6 Question 3

I do not have prior knowledge on determining molecular formulas from their names. I was also wondering about this, and if it is something we need to know how to do.
by Mary Gallo 1G
Mon Nov 09, 2020 5:54 pm
Forum: Student Social/Study Group
Topic: Mid-quarter Check in
Replies: 67
Views: 294

Re: Mid-quarter Check in

I'm lucky to have my midterms decently spread out among my classes, but the pace is definitely picking up. The content we are starting to go over in class is surpassing my previous knowledge so I've been getting a little frantic about keeping up. The concepts after Midterm 1 are not sticking with me...
by Mary Gallo 1G
Mon Nov 09, 2020 4:03 pm
Forum: Lewis Structures
Topic: Confused on a Symbol
Replies: 3
Views: 24

Re: Confused on a Symbol

The symbol is the Greek lowercase letter delta, δ, and is used to indicate partial charge. The atom with a greater electronegativity has a partial negative charge, and the atom with a lesser electronegativity has a partial positive charge.
by Mary Gallo 1G
Fri Nov 06, 2020 9:57 am
Forum: Student Social/Study Group
Topic: Favorite TV shows
Replies: 189
Views: 1216

Re: Favorite TV shows

The Walking Dead, How to Get Away With Murder, and Psych (not on Netflix, but one of the most genius shows ever) are some of my favorites! I just started The Queen's Gambit and wasn't sure if I'd like it, but it's really captivating!
by Mary Gallo 1G
Thu Nov 05, 2020 10:43 am
Forum: Formal Charge and Oxidation Numbers
Topic: Lewis structures and formal charge
Replies: 4
Views: 22

Re: Lewis structures and formal charge

Could someone explain a bit more on why atoms with high electron affinities would be more stable with a negative formal charge and vice versa? Thanks!
by Mary Gallo 1G
Wed Nov 04, 2020 11:07 am
Forum: Octet Exceptions
Topic: Boron
Replies: 8
Views: 159

Re: Boron

Boron is in group 13 of the periodic table so it only has 3 valence electrons. In order to maintain a formal charge of zero, it can only form 3 covalent bonds. It is actually less stable to have boron follow the octet rule because its formal charge would no longer be zero.
by Mary Gallo 1G
Wed Nov 04, 2020 10:36 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Equation
Replies: 16
Views: 72

Re: Formal Charge Equation

Adding on to above, when using the formal charge equation, make sure you are only applying it to one atom in the structure. So in terms of L (or the lone pairs) just count the dots around one specific atom because you are only calculating the formal charge for one atom at a time.
by Mary Gallo 1G
Wed Nov 04, 2020 10:23 am
Forum: Lewis Structures
Topic: Electrons in Lewis Structures
Replies: 8
Views: 41

Re: Electrons in Lewis Structures

Thank you both so much for the help! :)
by Mary Gallo 1G
Wed Nov 04, 2020 10:20 am
Forum: Lewis Structures
Topic: Sulfate Ion Lewis Structure
Replies: 3
Views: 21

Re: Sulfate Ion Lewis Structure

The sulfur atom in the sulfate ion can hold more than 8 electrons because atoms in period 3 or higher of the periodic table have d-orbitals in their valence shell. The octet guideline follows that the 8 electrons are filled in s and p orbitals (s2 p6 = 8 electrons). However, with the d-orbital in th...
by Mary Gallo 1G
Wed Nov 04, 2020 10:10 am
Forum: Lewis Structures
Topic: Electrons in Lewis Structures
Replies: 8
Views: 41

Electrons in Lewis Structures

When drawing Lewis Structures, what is a good rule of thumb for determining the amount of electrons to use for each element?
by Mary Gallo 1G
Wed Nov 04, 2020 9:54 am
Forum: Properties of Light
Topic: Study Advice
Replies: 50
Views: 306

Re: Study Advice

I think completing practice problems is one of the best ways to study because it mimics the calculations we have to complete on exams. This ensures that the steps for different kinds of problems are drilled into your mind. It's also a good idea to look over the lectures, or any notes you took on the...
by Mary Gallo 1G
Fri Oct 30, 2020 5:37 pm
Forum: *Shrodinger Equation
Topic: Midterm Scores
Replies: 30
Views: 337

Re: Midterm Scores

Do you think we will be able to see any questions we get wrong to review for the final?
by Mary Gallo 1G
Fri Oct 30, 2020 5:28 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation for ions?
Replies: 4
Views: 70

Re: Rydberg Equation for ions?

I believe that the Rydberg Equation can only be used for hydrogen atoms (or hydrogen-like species containing only one atom) because it stems from the Bohr model of a hydrogen atom. The Bohr model doesn't account for more than one electron or electron-electron interactions. Because He+ only has one e...
by Mary Gallo 1G
Thu Oct 29, 2020 2:59 pm
Forum: Administrative Questions and Class Announcements
Topic: Participation Points [ENDORSED]
Replies: 62
Views: 1045

Re: Participation Points [ENDORSED]

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? If you click on "Quick links" at the top right of the page you can select "Your posts" from the drop down menu. This will take you to a page that shows all of the...
by Mary Gallo 1G
Thu Oct 29, 2020 2:53 pm
Forum: Student Social/Study Group
Topic: Lavelle's Jokes
Replies: 18
Views: 248

Re: Lavelle's Jokes

I love making chemistry jokes, but I only do so periodically.
by Mary Gallo 1G
Thu Oct 29, 2020 2:51 pm
Forum: Student Social/Study Group
Topic: How to relax
Replies: 126
Views: 732

Re: How to relax

I think doing art (or something that you're passionate about) is a really nice way of relaxing. I find that it is nice to be focused on something other than school for a while.
by Mary Gallo 1G
Thu Oct 22, 2020 4:37 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Conceptual difference between momentum and velocity
Replies: 4
Views: 26

Re: Conceptual difference between momentum and velocity

Velocity measures the speed of an object (in a certain direction) and momentum is used to measure how much mass in in motion (as represented by mass x velocity). They both involve movement in a specified direction, however, momentum depends on mass whereas velocity is independent of mass.
by Mary Gallo 1G
Thu Oct 22, 2020 4:28 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: N1 and N2
Replies: 2
Views: 40

Re: N1 and N2

I was confused on the same thing but I got a lot of clarification on this forum:
https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=17&t=64748&sid=5cfe4a54eb50695e3b57ca5605232d1f
The responses were really helpful to me so I hope they can benefit you too!
by Mary Gallo 1G
Thu Oct 22, 2020 4:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Set Up
Replies: 3
Views: 42

Re: Midterm Set Up

Dr. Lavelle has recommended that we print out the periodic table and sheet of equations and constants that he emailed to us because we are not required to memorize that information for the midterm. Both of these sheets can be found on his website as well. I also put a link to them below: https://lav...
by Mary Gallo 1G
Thu Oct 22, 2020 3:59 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Energy of H-Atom Equations
Replies: 3
Views: 67

Re: Energy of H-Atom Equations

Thank you both so much, that was very helpful!
by Mary Gallo 1G
Thu Oct 22, 2020 11:42 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Calculator
Replies: 2
Views: 24

Re: Calculator

There isn't any content (at least on the first midterm) that has calculations involving radians or degrees so you should be fine in either mode. :)
by Mary Gallo 1G
Thu Oct 22, 2020 11:39 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Energy of H-Atom Equations
Replies: 3
Views: 67

Energy of H-Atom Equations

Hello! I wanted to conceptually understand the equations for H-atom energy more. I know that when calculating the energy emitted/absorbed by a H-atom we use En = -hR/n^2 and then use ΔE = E final - E initial. However, when using the equation: v (frequency) = R [ 1/(n1^2) - 1/(n2^2) ] is n1 always th...
by Mary Gallo 1G
Wed Oct 14, 2020 4:48 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post module #19
Replies: 2
Views: 30

Re: Post module #19

To solve this problem you will need to use Heisenberg's Indeterminacy Equation: Δp * Δx ≥ h/(4pi) h/(4pi) is just Planck's constant divided by 4pi. For the first part you would need to plug in the uncertainty in position of the electron (Δx), 1.7 x 10-15 m, and solve for the uncertainty in momentum ...
by Mary Gallo 1G
Wed Oct 14, 2020 4:34 pm
Forum: Properties of Light
Topic: intensity, photons, and frequency
Replies: 7
Views: 60

Re: intensity, photons, and frequency

Hi! Increasing the number of photons does not increase their frequency, just the intensity of the light. Instead, the frequency of an individual photon is proportional to the energy of that photon. Hope this helps!
by Mary Gallo 1G
Wed Oct 14, 2020 4:29 pm
Forum: Photoelectric Effect
Topic: Wavelength PhotoElectric Effect Question
Replies: 1
Views: 27

Re: Wavelength PhotoElectric Effect Question

Hi! I did my best to summarize the steps for each problem below: B) You know that an electron is only ejected once the frequency of radiation reaches 2.5x10^16 Hz. This means that we are solving for the energy required to eject an electron that is proportional to this frequency. Therefore, you would...
by Mary Gallo 1G
Tue Oct 13, 2020 5:48 pm
Forum: Properties of Light
Topic: Sapling Week 2/3 HW Question #5
Replies: 1
Views: 33

Re: Sapling Week 2/3 HW Question #5

Based on Dr. Lavelle's module on Atomic Spectra, we know that 1 line is formed for each state that an electron jumps, or the difference between the initial and final states. In this example, the electron returns to the n=1 level (ground state) from the n=7 level, which is a difference of 7-1, so 6 s...
by Mary Gallo 1G
Tue Oct 13, 2020 5:34 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Textbook problem 1A.15
Replies: 5
Views: 37

Re: Textbook problem 1A.15

I believe the n1 = 1 comes from the fact that ultraviolet electromagnetic radiation is in the Lyman series (where n1 = 1). However, I also do not quite understand how we determine what series to use. Is it something that we should have memorized?
by Mary Gallo 1G
Fri Oct 09, 2020 11:42 pm
Forum: Limiting Reactant Calculations
Topic: Determining Limiting Reactant
Replies: 4
Views: 34

Re: Determining Limiting Reactant

Thank you so much for the explanation!
by Mary Gallo 1G
Fri Oct 09, 2020 1:48 pm
Forum: Limiting Reactant Calculations
Topic: Determining Limiting Reactant
Replies: 4
Views: 34

Determining Limiting Reactant

Hi! When doing calculations to solve for the limiting reactant, should you always solve for the moles of product each reactant will make? Or can you just find the moles of each reactant available from given gram amounts? Thank you!
by Mary Gallo 1G
Tue Oct 06, 2020 3:31 pm
Forum: Limiting Reactant Calculations
Topic: Sapling HW 10
Replies: 3
Views: 60

Re: Sapling HW 10

I had different given values so I cannot confirm what answers are correct, but I got a different molar mass for 3-methyl-3-hexanol. The molecular formula is C7H16O so I calculated the molar mass to be 116.204 g/mol. Try using that molar mass to calculate the theoretical yield of 3-methyl-3-hexanol a...

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