Search found 19733 matches

by Chem_Mod
Tue Mar 16, 2021 7:02 pm
Forum: Administrative Questions and Class Announcements
Topic: THANK YOU DR LAVELLE!
Replies: 47
Views: 920

Re: THANK YOU DR LAVELLE!

Your tribute and thank-you slides are excellent!

Tonight I will enjoy reading more of them.
by Chem_Mod
Tue Mar 16, 2021 12:46 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 416
Views: 143888

Re: Saying Thank You to Dr. Lavelle

Thank you all!
We had a great two quarters!

Wishing you all the best.
by Chem_Mod
Tue Mar 16, 2021 10:25 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Frequency factor and Activation energy [ENDORSED]
Replies: 1
Views: 28

Re: Frequency factor and Activation energy [ENDORSED]

The preexponential/frequency parameter, A, is considered a separate parameter from activation energy, Ea, in the Arrhenius equation.
by Chem_Mod
Tue Mar 16, 2021 10:22 am
Forum: Administrative Questions and Class Announcements
Topic: Acids and Bases Review- Ty
Replies: 1
Views: 114

Re: Acids and Bases Review- Ty

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:20 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 9
Replies: 1
Views: 370

Re: Matthew's Workshop - Week 9

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:20 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 8
Replies: 1
Views: 258

Re: Matthew's Workshop - Week 8

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:20 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Kate's Midterm Review
Replies: 1
Views: 170

Re: Kate's Midterm Review

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:19 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 7
Replies: 1
Views: 431

Re: Matthew's Workshop - Week 7

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:17 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 6
Replies: 1
Views: 392

Re: Matthew's Workshop - Week 6

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:17 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 5
Replies: 1
Views: 344

Re: Matthew's Workshop - Week 5

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:17 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 3
Replies: 1
Views: 437

Re: Matthew's Workshop - Week 3

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:17 am
Forum: Administrative Questions and Class Announcements
Topic: Julia's Step-Up Session Week 3
Replies: 1
Views: 92

Re: Julia's Step-Up Session Week 3

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 10:16 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 2
Replies: 1
Views: 435

Re: Matthew's Workshop - Week 2

These were helpful. Thank you.
by Chem_Mod
Tue Mar 16, 2021 8:45 am
Forum: General Rate Laws
Topic: Manipulating rate law equations [ENDORSED]
Replies: 1
Views: 17

Re: Manipulating rate law equations [ENDORSED]

Working through examples is the best way to practice. Take a look at the example I did in class and the examples in the textbook, assigned problems in the textbook, and Sapling Learning.
by Chem_Mod
Tue Mar 16, 2021 8:42 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts and Intermediates
Replies: 1
Views: 13

Re: Catalysts and Intermediates

Michael Iter 2F wrote:For example, could there maybe be a molecule that appears as an intermediate and then catalyzes the subsequent steps of the reaction?


Yes that is possible.
by Chem_Mod
Tue Mar 16, 2021 8:40 am
Forum: Zero Order Reactions
Topic: Sapling #4 (week 9/10) [ENDORSED]
Replies: 4
Views: 32

Re: Sapling #4 (week 9/10) [ENDORSED]

Good answer.
by Chem_Mod
Tue Mar 16, 2021 1:16 am
Forum: Administrative Questions and Class Announcements
Topic: THANK YOU DR LAVELLE!
Replies: 47
Views: 920

Re: THANK YOU DR LAVELLE!

I am thankful for so many terrific students.

I am reading and enjoying each slide one at a time. They are so well done. Creative!

Spacing out my reading of them, some each night, to enjoy them.

Great to see many TA and UA acknowledgments.

:-)
by Chem_Mod
Tue Mar 16, 2021 1:07 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy [ENDORSED]
Replies: 2
Views: 29

Re: Activation Energy [ENDORSED]

Great answer Amanda.
Dr. DJ LL :-)
by Chem_Mod
Tue Mar 16, 2021 1:04 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate determining step [ENDORSED]
Replies: 3
Views: 27

Re: Rate determining step [ENDORSED]

Good answer.
by Chem_Mod
Tue Mar 16, 2021 12:34 am
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Cut Off [ENDORSED]
Replies: 1
Views: 106

Re: Chem Community Cut Off [ENDORSED]

As announced, I extended the Chemistry Community and Sapling deadline to Tuesday morning 9am.

Good answers to Chemistry Community questions will count for missing Chemistry Community points for the quarter.
by Chem_Mod
Sun Mar 14, 2021 8:35 pm
Forum: Administrative Questions and Class Announcements
Topic: THANK YOU DR LAVELLE!
Replies: 47
Views: 920

Re: THANK YOU DR LAVELLE!

I AM SPEACHLESS.

WoW.

I have no idea how to respond to this website :-) https://docs.google.com/presentation/d/ ... c2814b_1_0

THANK YOU!!!
by Chem_Mod
Sun Mar 14, 2021 8:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 416
Views: 143888

Re: Saying Thank You to Dr. Lavelle

Dear Dr. Lavelle, all the TA's, UA's, and staff who helped make online school possible, Thank you for all of your hard work! With everything going on during this pandemic, I was anxious about being unable to learn or do well in the course. However, you all went above and beyond during these last tw...
by Chem_Mod
Sun Mar 14, 2021 8:15 pm
Forum: General Science Questions
Topic: 14B vs. 14C material
Replies: 6
Views: 75

Re: 14B vs. 14C material

14A material will definitely be on the MCAT and probably other standardized STEM exams. LS 7A touches slightly on 14A material with intermolecular forces and stuff. Chem 14D requires basic knowledge of 14A (mostly acid/base knowledge). Chem 153A (biochem) goes over some intermolecular forces from 14...
by Chem_Mod
Sun Mar 14, 2021 8:07 pm
Forum: General Science Questions
Topic: 14B vs. 14C material
Replies: 6
Views: 75

Re: 14B vs. 14C material

14C does not cover 14B material; 14C builds mainly on 14A. 14B material shows up again in Physics 5B, Chem 14BL, and the MCAT too, so it's not a bad idea to keep your notes!
by Chem_Mod
Sun Mar 14, 2021 6:43 pm
Forum: Administrative Questions and Class Announcements
Topic: THANK YOU DR LAVELLE!
Replies: 47
Views: 920

Re: THANK YOU DR LAVELLE!

Remote learning survey said to contact department for teaching award nominations.
Email to send for Chem nominations: chair@chem.ucla.edu
by Chem_Mod
Sun Mar 14, 2021 6:27 pm
Forum: Student Social/Study Group
Topic: Mood after finishing gen chem
Replies: 1
Views: 40

Re: Mood after finishing gen chem

:-)

Looks like Good Chemistry to me!
by Chem_Mod
Sun Mar 14, 2021 6:10 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 416
Views: 143888

Re: Saying Thank You to Dr. Lavelle

Janna Shakiba wrote:Dr. Lavelle, thank you for making me enjoy chemistry for the first time in my LIFE!


lol

It is, what I call, Good Chemistry!

:-)
by Chem_Mod
Sun Mar 14, 2021 4:53 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 416
Views: 143888

Re: Saying Thank You to Dr. Lavelle

I'm taking a break from writing my soc paper to tell you, Dr. Lavelle, that I could not be more appreciative of you. Chem 14A and 14B would not have been the same without your amazing energy and commitment to teaching. Your music was awesome, the UA sessions were a life saver, and the only thing th...
by Chem_Mod
Sun Mar 14, 2021 2:21 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 416
Views: 143888

Re: Saying Thank You to Dr. Lavelle

Thank you for all the wonderful posts and positive feedback. It encourages me to continue my focused and significant efforts to assist students.
by Chem_Mod
Sun Mar 14, 2021 9:09 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: textbook 6.73 [ENDORSED]
Replies: 1
Views: 51

Re: textbook 6.73 [ENDORSED]

The textbook discusses the aluminum-air fuel cell: anode: 6OH-(aq) + 2Al(s) --> 2Al(OH)3 (aq) + 6e- cathode: 3H2O(l) + (3/2)O2(g) + 6e ---> 6OH- (aq) overall: 3H2O(l) + 2Al(s) + (3/2)O2(g) --> 2Al(OH)3 (aq) Ecell = E cathode - E anode = (0.40V) - (-1.66V) = +2.06V All standard reduction half-reactio...
by Chem_Mod
Sun Mar 14, 2021 8:49 am
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Focus 6 Exercises (53, 57, 73) [ENDORSED]
Replies: 1
Views: 50

Re: Focus 6 Exercises (53, 57, 73) [ENDORSED]

6.53 The anode side is the product side (reaction starts with lower concentration product), 0.0010 M CrCl3(aq). Diluting [P] therefore makes Q << 1, which makes ln Q even more negative, and therefore E more positive. Work through the concentration cell example I did in class. Lower concentration pro...
by Chem_Mod
Sun Mar 14, 2021 7:49 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.3 Part (d) Question [ENDORSED]
Replies: 1
Views: 32

Re: 6L.3 Part (d) Question [ENDORSED]

All half reactions are given in the list of standard reduction potentials. Students do not need to 'know/memorize' the reactions. This makes it much easier and straight forward to figure out the anode (oxidation half-reaction), the cathode (reduction half-reaction), and the overall redox reaction. W...
by Chem_Mod
Sun Mar 14, 2021 7:34 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M Exercises (5, 7, 11) [ENDORSED]
Replies: 2
Views: 39

Re: 6M Exercises (5, 7, 11) [ENDORSED]

Great answers. Whenever (aq) is given it means water is present and therefore no need to explicitly state H 2 O. When (aq) is stated then that means water is present and can be part of the redox reaction. The oxygen atom in water is 2- oxidation state. The oxygen atom in O2(g) is zero oxidation stat...
by Chem_Mod
Sun Mar 14, 2021 7:27 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook 6L.7b [ENDORSED]
Replies: 2
Views: 56

Re: Textbook 6L.7b [ENDORSED]

Your reaction is not balanced.
by Chem_Mod
Sun Mar 14, 2021 7:21 am
Forum: Balancing Redox Reactions
Topic: balancing redox rxns [ENDORSED]
Replies: 1
Views: 83

Re: balancing redox rxns [ENDORSED]

This is a harder one to figure out with the information given. If one was given the cell diagram then straight forward. Ag(s) is the same electrode for anode and cathode. What makes the two half-reactions different are the solutions (electrolytes) the electrodes are in. Ag(s) anode is in contact wit...
by Chem_Mod
Sat Mar 13, 2021 10:41 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Textbook 7.1 [ENDORSED]
Replies: 1
Views: 61

Re: Textbook 7.1 [ENDORSED]

The reason why kinetic control would predominate at low temperatures is because of activation energies. If you look at the graphs that you have, the green line has a lower activation energy barrier. You can think of a lower activation energy as occurring "faster", so as you said, because t...
by Chem_Mod
Sat Mar 13, 2021 10:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Net Ionic Equations? [ENDORSED]
Replies: 1
Views: 43

Re: Net Ionic Equations? [ENDORSED]

Yes, when you are writing equilibrium constants, you should be using the net ionic equation!
by Chem_Mod
Sat Mar 13, 2021 8:10 pm
Forum: Student Social/Study Group
Topic: Thank You and Good Luck
Replies: 1
Views: 36

Re: Thank You and Good Luck

Thank you and all the best to all my students.
by Chem_Mod
Sat Mar 13, 2021 6:31 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Difference btwn constant p calorimetry and aconstant v calorimetry [ENDORSED]
Replies: 1
Views: 38

Re: Difference btwn constant p calorimetry and aconstant v calorimetry [ENDORSED]

Remember that enthalpy is at constant pressure, so when doing calorimetry at constant pressure, you will be able to find enthalpy values.
by Chem_Mod
Sat Mar 13, 2021 6:27 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Textbook 7O.1
Replies: 1
Views: 42

Re: Textbook 7O.1

Can you let us know which part you need help with, instead of just writing the question. Just so we can have direction. Thanks :)
by Chem_Mod
Sat Mar 13, 2021 5:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell vs Concentration Cell
Replies: 4
Views: 38

Re: Galvanic Cell vs Concentration Cell

A concentration cell is made of two half-cells with the same electrodes but different concentrations of chemical species. This is done in order to create a concentration gradient of electrons wherein an equilibrium is reached through the flow of electrons. Through this flow of electrons, a redox rea...
by Chem_Mod
Fri Mar 12, 2021 7:11 pm
Forum: General Rate Laws
Topic: Lecture 26 [ENDORSED]
Replies: 1
Views: 353

Re: Lecture 26 [ENDORSED]

From the balanced chemical equation: unique rate = 1/2 (d[P]/dt) In class I wrote it as the rate of formation of product (d[P]/dt). I could have left it as the unique rate and not multiplied by 2. The most important part is they both match the experimentally determined rate law. The factor of 2 is t...
by Chem_Mod
Fri Mar 12, 2021 5:22 pm
Forum: General Rate Laws
Topic: Intermediate OH- present in overall rate law [ENDORSED]
Replies: 2
Views: 26

Re: Intermediate OH- present in overall rate law [ENDORSED]

Water always has HO- and H3O+ present, and therefore can show in rate laws when the reaction rate is pH dependent.
by Chem_Mod
Fri Mar 12, 2021 2:17 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 234
Views: 120578

Re: Advice from a Medical Student [ENDORSED]

I wanted to write thank you on here! I keep re-reading this post because it helps me gain back motivation when I feel too defeated and scared about the future as a pre-med student. It’s been a lot of refreshing this page, but hopefully I can get through it! Hi Michelle, I am so glad you found this ...
by Chem_Mod
Fri Mar 12, 2021 2:08 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 225
Views: 18153

Re: Advice from a Medical Student - Part II [ENDORSED]

Hello! I'm Anthony, a first year Neuroscience major. I really appreciate your story and I love people who are trying to help young aspiring people learn and grow. Hi Anthony, thank you so much for the compliment. I hope this is helpful. If you have any questions or need advice moving forward, wheth...
by Chem_Mod
Fri Mar 12, 2021 12:21 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Kate's Chem 14B Final Review
Replies: 1
Views: 81

Kate's Chem 14B Final Review

Hello everyone, I attached my final review worksheet and answer key below. I hope you found these UA sessions helpful and I had so much fun getting to know all of you! Thank you for making me laugh during our sessions and bringing a smile to my face every week. Please say hi in the fall and I know y...
by Chem_Mod
Thu Mar 11, 2021 8:07 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Textbook 6.57 Question about Favorability, choosing Cathode, anode
Replies: 3
Views: 30

Re: Textbook 6.57 Question about Favorability, choosing Cathode, anode

Normally if you are determining the cell potential of a Galvanic cell, you want the most positive cell potential. However, in this problem, you are not constructing a Galvanic cell; instead, you are simply trying to find Ka for HF. The K that you find using the Nernst equation is for double the reac...
by Chem_Mod
Thu Mar 11, 2021 7:45 pm
Forum: Calculating Work of Expansion
Topic: W= -PDeltaV
Replies: 15
Views: 69

Re: W= -PDeltaV

Use this equation when the volume change is occurring under constant pressure conditions. Since the pressure is constant, it will be irreversible expansion/compression.
by Chem_Mod
Thu Mar 11, 2021 7:43 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Textbook Question 6.53
Replies: 2
Views: 16

Re: Textbook Question 6.53

Remember in a concentration cell, the driving force behind the redox reaction is the difference in concentration between the two cells. The reaction proceeds to equalize the two concentrations, so ions will form on the side with fewer ions to start with (lower CrCl3 concentration). From this informa...
by Chem_Mod
Thu Mar 11, 2021 6:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Potentials as State Functions
Replies: 1
Views: 18

Re: Cell Potentials as State Functions

E and E0 are not state functions. They depend on what exactly is oxidized or reduced, which is why you can subtract the reduction potentials for two half-reactions to get cell potential for an overall reaction. However, you cannot add the cell potentials for two overall reactions together to get the...
by Chem_Mod
Thu Mar 11, 2021 6:28 pm
Forum: Balancing Redox Reactions
Topic: Self Test 6K.1A
Replies: 1
Views: 23

Re: Self Test 6K.1A

It would be helpful to see what work you already had done in this problem. First write out the reactants and products as given by the problem, unbalanced: Cu + NO3- --> Cu(NO3)2 + NO (we can omit the H+ from HNO3 as it is a spectator ion, remembering that nitric acid is a strong acid which completel...
by Chem_Mod
Thu Mar 11, 2021 6:19 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Textbook 7.9
Replies: 1
Views: 29

Re: Textbook 7.9

In future posts, please include the relevant part of the problem as well. The difference between the two mechanisms is one is dependent on the concentration of H2O while the other is not. When you do the reaction in a dilute solution of sucrose, this means there is a huge amount of water available c...
by Chem_Mod
Thu Mar 11, 2021 6:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.9
Replies: 1
Views: 20

Re: 6L.9

In future posts, please include the relevant part of your question as well. In many cases, you need to go off the reduction reactions given to you. Look up the reduction reactions for each of the species in question, determine which reactions are possible based on the species that the problem tells ...
by Chem_Mod
Thu Mar 11, 2021 6:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: textbook problem 6L.3 (d)
Replies: 1
Views: 47

Re: textbook problem 6L.3 (d)

I am not clear on what your question is. Perhaps this past post may help clarify your issue: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=75817 If you are asking why H+ is not on the products side in the anode half-reaction, think about what is getting oxidized and what it is getting oxidized...
by Chem_Mod
Thu Mar 11, 2021 5:10 pm
Forum: Administrative Questions and Class Announcements
Topic: [CHEM 14B KARAOKE]
Replies: 68
Views: 2267

Re: [CHEM 14B KARAOKE]

This was just published: https://www.chemistry.ucla.edu/news/karaoke-fun-%E2%80%9Cdj-lavelle%E2%80%9D Great event, photos, students, … read the article for details. Well Done all Contestants! Many thanks and shout out to event organizers Adila Ahmed, Andre Fabian, Mackenzie Van Valkenburgh, Alette E...
by Chem_Mod
Thu Mar 11, 2021 5:09 pm
Forum: Administrative Questions and Class Announcements
Topic: [KARAOKE UPDATE]
Replies: 3
Views: 61

Re: [KARAOKE UPDATE]

This was just published: https://www.chemistry.ucla.edu/news/karaoke-fun-%E2%80%9Cdj-lavelle%E2%80%9D Great event, photos, students, … read the article for details. Well Done all Contestants! Many thanks and shout out to event organizers Adila Ahmed, Andre Fabian, Mackenzie Van Valkenburgh, Alette E...
by Chem_Mod
Thu Mar 11, 2021 2:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Quiz Question
Replies: 1
Views: 44

Re: Quiz Question

Because CO2 is the only non solid, the equilibrium expression is Kp=CO2. Use PV=nRT from here to solve.
by Chem_Mod
Thu Mar 11, 2021 1:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Michael's thermochemistry workshop
Replies: 2
Views: 49

Re: Michael's thermochemistry workshop

You have the exact right line of reason for this problem! The only mistake that you made is that the problem states that only half of the ice cream gets melted. Therefore, the mass you use when you multiply by deltaHfus should be 125/2 g! However, the first mass you use in the mc(deltaT) term is sti...
by Chem_Mod
Thu Mar 11, 2021 1:46 pm
Forum: Calculating Work of Expansion
Topic: Michael Nguyen
Replies: 1
Views: 72

Re: Michael Nguyen

Hi Claire,

Feel free to email me at micngu@ucla.edu if you have a specific question you want to ask me! Also, I have all of my sessions in my Google Drive folder, and you might be able to find what you are looking for in those files as well!

-Michael
by Chem_Mod
Thu Mar 11, 2021 11:41 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Lecture 26 Question [ENDORSED]
Replies: 1
Views: 31

Re: Lecture 26 Question [ENDORSED]

From the balanced chemical equation: unique rate = 1/2 (d[P]/dt) In class I wrote it as the rate of formation of product (d[P]/dt). I could have left it as the unique rate and not multiplied by 2. They both match the experimentally determined rate law. The factor of 2 is the difference between writi...
by Chem_Mod
Thu Mar 11, 2021 11:08 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Sapling Learning Week 9 and 10 Homework Question 13
Replies: 1
Views: 37

Re: Sapling Learning Week 9 and 10 Homework Question 13

Start by writing the slow step rate law, which would be rate=k[HClO][I-]. [HClO] needs to be substituted because intermediates do not belong in the rate law. The first step can be used to achieve this. Write the rate forward and reverse for step 1. Then, rearrange and isolate [HClO]. Substitute this...
by Chem_Mod
Thu Mar 11, 2021 11:08 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Book 6L.9
Replies: 1
Views: 15

Re: Book 6L.9

In order to produce the cell diagram, you need to write the two half reactions. Start with MnO4- to Mn+2, then balance the oxygens, hydrogens, and electrons. The second half reaction is Fe+2 to Fe+3, which only requires the addition of electrons to one side. Coefficients are not necessary in the cel...
by Chem_Mod
Thu Mar 11, 2021 11:03 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook 6.43 (a)
Replies: 2
Views: 15

Re: Textbook 6.43 (a)

Think about this in terms of the equation E= Ecell - RT/nF ln Q. In this way, you can see that Ecell does not change as the reaction proceeds. Whereas, E is related to the equilibrium progression of the reaction through Q.
by Chem_Mod
Thu Mar 11, 2021 10:01 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Textbook 6.57
Replies: 1
Views: 22

Re: Textbook 6.57

The F2 half reaction is given, so you know that this is one of the half reactions. We now need an expression that described HF. Write the HF half reaction in the reduction direction to compare the two reduction potentials and determine which is the anode and which is the cathode.
by Chem_Mod
Thu Mar 11, 2021 9:58 am
Forum: General Rate Laws
Topic: Textbook 7.11A
Replies: 2
Views: 18

Re: Textbook 7.11A

Because the rate law is given, write the rate law in different scenarios to determine which step is slow. For example, write if step 1 were slow, step 2 were slow, or step 3 were slow. Then see which matches the proposed rate law.
by Chem_Mod
Thu Mar 11, 2021 9:56 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7.11 Textbook
Replies: 2
Views: 16

Re: 7.11 Textbook

The goal is to determine which is the slow step based on the proposed mechanism. Try writing the rate law if step 1 was slow, step 2 was slow, or if step 3 was slow. Then determine which scenario matches the given rate law.
by Chem_Mod
Thu Mar 11, 2021 9:54 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Week 10 Sapling #13
Replies: 2
Views: 33

Re: Week 10 Sapling #13

You are right that HClO is an intermediate. Start by writing the slow step rate law, which would be rate=k[HClO][I-]. [HClO] needs to be substituted because intermediates do not belong in the rate law. The first step can be used to achieve this. Write the rate forward and reverse for step 1. Then, r...
by Chem_Mod
Thu Mar 11, 2021 8:47 am
Forum: Administrative Questions and Class Announcements
Topic: Matthew's notes?
Replies: 1
Views: 59

Re: Matthew's notes?

Hi Garmani,

There seemed to be an issue uploading that last night; I think I fixed it now!

-Matt
by Chem_Mod
Thu Mar 11, 2021 7:34 am
Forum: Administrative Questions and Class Announcements
Topic: Acids and Bases Review- Ty
Replies: 1
Views: 114

Acids and Bases Review- Ty

Hi everyone,

Here are the slides I went over in my review session on Tuesday. Hope they help in your studying!

-Ty
by Chem_Mod
Wed Mar 10, 2021 11:55 pm
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 10
Replies: 1
Views: 783

Re: Matthew's Workshop - Week 10

Hi everyone, My session notes/answers are posted! I also included an extra explanation for 4(d) post-workshop using kinetics, so hopefully the answer is doubly clear :). Thank you again for being such amazing students; it's been a pleasure being one of your UAs for the past two quarters. Good luck o...
by Chem_Mod
Wed Mar 10, 2021 8:47 pm
Forum: General Rate Laws
Topic: Final Lecture Clarification
Replies: 1
Views: 20

Re: Final Lecture Clarification

In class I wrote it as the rate of formation of product. I could have left it as the unique rate and not multiplied by 2. They both match the experimentally determined rate law. The factor of 2 is the difference between writing the unique rate versus the rate of change of product concentration. K = ...
by Chem_Mod
Wed Mar 10, 2021 7:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Question about Today's Lecture - Why multiply by 2? [ENDORSED]
Replies: 1
Views: 236

Re: Question about Today's Lecture - Why multiply by 2? [ENDORSED]

In class I wrote it as the rate of formation of product.

I could have left it as the unique rate and not multiplied by 2.

They both match the experimentally determined rate law.

The factor of 2 is the difference between writing the unique rate versus the rate of change of product concentration.
by Chem_Mod
Wed Mar 10, 2021 5:25 pm
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 10
Replies: 1
Views: 783

Matthew's Workshop - Week 10

Hi everyone! We've finally made it to Week 10! :D Here's the worksheet for today's session. We will be covering the rest of kinetics, but of course since the final is on Sunday I'll try to have some time to answer questions about any previous material. *Session Work and Answers were posted Thursday ...
by Chem_Mod
Wed Mar 10, 2021 3:43 pm
Forum: General Rate Laws
Topic: intermediates in rate laws
Replies: 5
Views: 18

Re: intermediates in rate laws

Typically, the concentration of an intermediate is not something you have control over or even have an ability to measure throughout a reaction. Thus in a rate law, it is not useful to have the concentrations of intermediates. The concentrations of the reactants are what you can control and change i...
by Chem_Mod
Wed Mar 10, 2021 3:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Memorizing an Equation
Replies: 4
Views: 41

Re: Memorizing an Equation

This equation can be easily derived from the Arrhenius equation (which is on the formula sheet). k = Ae^{-E_{a}/RT} If you have two different rate constants at two different temperatures for the same reaction, their ratio is given by \frac{k_{2}}{k_{1}} = \frac{Ae^{-E_{a}/RT_{2}}}{Ae^{-E_{a}/RT_{1}}...
by Chem_Mod
Wed Mar 10, 2021 3:28 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 6D.15
Replies: 2
Views: 25

Re: 6D.15

Correct- to solve these problems, you will need to refer to the table to find the K a or K b values. In this case specifically, for something like NH 4 Cl, this is actually a salt of NH 4 + and Cl - . Thus you'll have to look up the K a of NH 4 + , but you won't actually find this in the table. You ...
by Chem_Mod
Wed Mar 10, 2021 11:58 am
Forum: Administrative Questions and Class Announcements
Topic: Acid and Base Review (Julia's Step-Up Session)
Replies: 1
Views: 98

Acid and Base Review (Julia's Step-Up Session)

Hello! As requested, I have attached the answer key from today's review on acids and bases. The link to the worksheet is also included in the beginning of the document. Please let me know if you have any questions about the worksheet. I wish you all the best on the final and the rest of your classes...
by Chem_Mod
Wed Mar 10, 2021 11:54 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equilibrium approach [ENDORSED]
Replies: 3
Views: 26

Re: Pre-equilibrium approach [ENDORSED]

If the 1st step is slow then no need for any approximation. Rate law won't have intermediate in it.
by Chem_Mod
Wed Mar 10, 2021 11:52 am
Forum: General Rate Laws
Topic: Textbook Question 7A. 17
Replies: 4
Views: 23

Re: Textbook Question 7A. 17

You can use experiments 1 and 3 to find that the reaction is second order with respect to B. When you compare the rate law expressions of the two experiments, you end up simplifying it to 0.4139^n = 0.171. You can then solve for n by taking the log of both sides to get nlog(0.4139) = 0.171, which ge...
by Chem_Mod
Wed Mar 10, 2021 11:52 am
Forum: Experimental Details
Topic: Fast step at equilibrium [ENDORSED]
Replies: 4
Views: 53

Re: Fast step at equilibrium [ENDORSED]

As I discussed in class step 2 is slow. Therefore product formed in step 1 builds up. Product can go back to reactant in step 1. Since forward and reverse reactions are occurring and step 1 is treated as approximately at equilibrium.
by Chem_Mod
Wed Mar 10, 2021 11:46 am
Forum: General Rate Laws
Topic: textbook problem 7.A. 15 part a
Replies: 4
Views: 15

Re: textbook problem 7.A. 15 part a

If you compare experiments 1 and 4, you'll find that the reaction is 0th order with respect to C. This means that when solving for the rest of the reaction orders, we can omit C because the concentrations of C will just equal 1.

Hope this helps!
by Chem_Mod
Wed Mar 10, 2021 11:17 am
Forum: Administrative Questions and Class Announcements
Topic: Suggestion for future
Replies: 1
Views: 41

Re: Suggestion for future

Thanks for the useful suggestion. Note that the UAs did do review the week of midterm 1, the week of midterm 2, and the week of the final. So those three weeks do a lot of review. There are pros and cons. Some students cannot attend specific times covering review of topic X. They then request that t...
by Chem_Mod
Wed Mar 10, 2021 11:01 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: textbook 6N.3 [ENDORSED]
Replies: 2
Views: 88

Re: textbook 6N.3 [ENDORSED]

I had questions for parts (a) and (c). The problem states: Predict the potential of each of the following cells: (a) Pt(s)|H2(g, 1.0 bar)|HCl(aq, 0.075 mol/L)||HCl(aq, 1.0 mol/L)|H2(g, 1.0 bar)|Pt(s) For this one, when finding the standard potential first, does the Cl in HCl not matter and that's w...
by Chem_Mod
Wed Mar 10, 2021 11:00 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Writing Out Cell Diagrams
Replies: 3
Views: 35

Re: Writing Out Cell Diagrams

An inert conductive electrode (such as Pt) must be added to a cell when there is no other way of conducting electrons. Electrons need to get from one side of the cell to the other, and this is done by first conducting through one electrode, then the wire, then conducting through the other electrode....
by Chem_Mod
Wed Mar 10, 2021 10:44 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Is there a catalyst in this mechanism? [ENDORSED]
Replies: 6
Views: 67

Re: Is there a catalyst in this mechanism? [ENDORSED]

Thanks. I wanted to check question was correct.

Yes water is the catalyst in this reaction.
Without water the reaction does not occur.
by Chem_Mod
Wed Mar 10, 2021 10:38 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Focus Problem 7.21
Replies: 2
Views: 21

Re: Focus Problem 7.21

(f) initial rate against [A] for a reaction that is 1st order in A = a graph that shows how initial rate of a reaction varies with different values of [A]. The corresponding formula would be rate = k[A]^1, which k being a constant. [A] is raised to the first because it is a first order reaction. Thi...
by Chem_Mod
Wed Mar 10, 2021 10:32 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Focus Problem 7.11 [ENDORSED]
Replies: 1
Views: 50

Re: Focus Problem 7.11 [ENDORSED]

Step 1 cannot be the slow step as it does not match the given rate law.

Therefore, look at next step.

In Step 2 one needs to substitute out the intermediate, and when you do it matches the given rate law.

Answer is Step 2 is the slow step.

I will do a very similar example today in class.
by Chem_Mod
Wed Mar 10, 2021 10:24 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Textbook 7D.5 [ENDORSED]
Replies: 1
Views: 21

Re: Textbook 7D.5 [ENDORSED]

It can solved using either ratio.
by Chem_Mod
Wed Mar 10, 2021 10:05 am
Forum: First Order Reactions
Topic: Sapling Week 9/10 #11, Part 2 [ENDORSED]
Replies: 3
Views: 62

Re: Sapling Week 9/10 #11, Part 2 [ENDORSED]

Thanks Sid.
Good Chemistry.
:-)
by Chem_Mod
Wed Mar 10, 2021 10:01 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Initial Rates = Maximum rates [ENDORSED]
Replies: 9
Views: 123

Re: Initial Rates = Maximum rates [ENDORSED]

Good answers. Good Chemistry. :-)
by Chem_Mod
Wed Mar 10, 2021 9:54 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Intermediates? [ENDORSED]
Replies: 4
Views: 47

Re: Reaction Intermediates? [ENDORSED]

Intermediates are species that are in the mechanism, but not in the overall rate law. The way to distinguish intermediates and catalysts is that intermediates are always produced by a reaction, and then consumed immediately after in the next reaction. On the other hand, catalysts are consumed first...
by Chem_Mod
Wed Mar 10, 2021 7:36 am
Forum: Administrative Questions and Class Announcements
Topic: trick
Replies: 6
Views: 103

Re: trick

Click on chem_mod post number and you can see all chem_mod posts.
by Chem_Mod
Wed Mar 10, 2021 7:28 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Exergonic vs Exothermic [ENDORSED]
Replies: 4
Views: 64

Re: Exergonic vs Exothermic [ENDORSED]

Exergonic and endergonic usually refer to Gibbs free energy. Endothermic & exothermic refer to enthalpy. I remember it because exergonic & endergonic have "g" like Gibbs while endothermic & exothermic have "th" like enthalpy. Good one. Thanks for sharing. I should us...
by Chem_Mod
Wed Mar 10, 2021 7:08 am
Forum: Administrative Questions and Class Announcements
Topic: [CHEM 14B KARAOKE]
Replies: 68
Views: 2267

Re: [CHEM 14B KARAOKE]

Well Done!

Go to advanced search