Search found 108 matches
- Sun Mar 07, 2021 8:49 pm
- Forum: Student Social/Study Group
- Topic: Almost through!
- Replies: 8
- Views: 750
Re: Almost through!
Thanks Brianna! I'm proud of myself for putting myself out there to meet new people this quarter, which has been tough to do online. One example of that was through the chem karaoke we had yesterday! :) I hope the quarter has gone well for you too!
- Sun Mar 07, 2021 8:39 pm
- Forum: Balancing Redox Reactions
- Topic: Lecture 18 Minute 30
- Replies: 3
- Views: 196
Re: Lecture 18 Minute 30
No, in this method you just combine the E of the cathode and the anode, which is why you make the E of the anode -0.34. In the previous example in that lecture, you subtract the anode value from the cathode value, but you do not make it negative, as the subtraction does that for you. Essentially, by...
- Sun Mar 07, 2021 8:35 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Galvanic Cells
- Replies: 3
- Views: 260
Re: Galvanic Cells
Hi! I haven't watched this all the way through, but if you're a fan of Crash Course videos, I found one on electrochemistry that seems pretty helpful! Here's the link: https://youtu.be/IV4IUsholjg
- Sun Mar 07, 2021 8:28 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Delta H and Delta S both positive
- Replies: 31
- Views: 8084
Re: Delta H and Delta S both positive
When Delta H and Delta S are both positive, the reaction is spontaneous at high temperatures and not spontaneous at lower temperatures. The exact temperature at which the reaction will start to react spontaneously can be determined by using the equation Delta G=Delta H-T(Delta S).
- Sun Mar 07, 2021 8:26 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridges
- Replies: 12
- Views: 536
Re: Salt Bridges
Hi! Salt bridges connect the anode and cathode and are significant because they neutralize both the oxidation and reduction solutions. Without a salt bridge, the oxidation side would build up a negative charge and the reduction side would build up a positive charge.
- Sun Feb 28, 2021 12:36 pm
- Forum: Student Social/Study Group
- Topic: How to Reduce Nervousness before getting results
- Replies: 63
- Views: 4733
Re: How to Reduce Nervousness before getting results
Hi! A lot of times after a midterm, I will go through and trying to double-check my answers on the test and give myself an idea of how many I got right or wrong. I've personally had to stop doing this because of stress, but if it worries you to not remember what you did on the test, this can be a go...
- Sun Feb 28, 2021 12:29 pm
- Forum: Calculating Work of Expansion
- Topic: Finding Reversibility
- Replies: 8
- Views: 468
Re: Finding Reversibility
I believe that one way to tell is to see if the reaction is at equilibrium; in my notes for Week 4 Lecture 2, I have that if the reaction is at equilibrium, then it is a reversible process.
- Sun Feb 28, 2021 12:25 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Gibbs Free Energy Equation and n
- Replies: 13
- Views: 575
Re: Gibbs Free Energy Equation and n
In this equation, n is the moles of electrons transferred per one mole of reaction. Make sure that your redox reaction is balanced in order to get the correct number of moles of e-.
- Sun Feb 28, 2021 12:21 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Sapling Week 7/8 #19
- Replies: 3
- Views: 255
Re: Sapling Week 7/8 #19
I believe you would use the equation ΔG∘=-nFE and rearrange it so that you are solving for E. If you click on the 'hint' button on Sapling, it should tell you the number of moles of electrons transferred, which you can plug in for n.
- Sun Feb 28, 2021 11:35 am
- Forum: Administrative Questions and Class Announcements
- Topic: [CHEM 14B KARAOKE]
- Replies: 68
- Views: 5728
Re: [CHEM 14B KARAOKE]
Can’t wait to see everyone there!! It’s going to be a blast!
- Sun Feb 21, 2021 11:53 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy value
- Replies: 17
- Views: 821
Re: Entropy value
Entropy is the measure of how disordered a system is. The numerical value is significant; a larger negative value will mean a greater change in entropy than a smaller negative value, as will a larger positive entropy than a smaller positive one. At equilibrium, the total entropy of a reaction will b...
- Sun Feb 21, 2021 11:51 pm
- Forum: Student Social/Study Group
- Topic: Winter GEs?
- Replies: 33
- Views: 2503
Re: Winter GEs?
If Musicology 5 is offered, I would highly recommend taking it (especially with Professor Holmes)! It fills the Visual & Performing Arts GE and is super easy and fun.
- Sun Feb 21, 2021 5:39 pm
- Forum: Calculating Work of Expansion
- Topic: Work Formula
- Replies: 15
- Views: 753
Re: Work Formula
You only consider moles of gas for delta n because you are working with the ideal gas equation. Also, if you are finding the work of expansion, then a gas is the only thing that expand considerably, so it makes sense to only use moles of gas.
- Sun Feb 21, 2021 5:37 pm
- Forum: Balancing Redox Reactions
- Topic: Anode and Cathode
- Replies: 11
- Views: 482
Re: Anode and Cathode
Yes, the anode will always be the oxidation side of the reaction, because the electrons leave the anode and flow towards the positively charged cathode.
- Sun Feb 21, 2021 5:31 pm
- Forum: Calculating Work of Expansion
- Topic: Value of Q
- Replies: 20
- Views: 911
Re: Value of Q
You calculate Q in the same way you calculate K; it is the concentration of the products, to the power of their stoichiometric coefficient, over the concentration of the reactants to their stoichiometric coefficients.
- Sun Feb 21, 2021 5:25 pm
- Forum: Van't Hoff Equation
- Topic: Celcius vs Kelvin for T1 and T2
- Replies: 84
- Views: 6453
Re: Celcius vs Kelvin for T1 and T2
It is always better to use Kelvin since it is the SI unit for temperature. Also, since R is units of J/mol*K, you want to use Kelvin so that the units cancel out.
- Sun Feb 21, 2021 5:22 pm
- Forum: Student Social/Study Group
- Topic: Post Midterm 2 De-stressing
- Replies: 92
- Views: 6122
Re: Post Midterm 2 De-stressing
I watched WandaVision right after I finished the test—it was the perfect way to de-stress! I also treated myself to a fun weekend with my roommates (though now I have to kick it back into gear for Week 8). :)
- Sun Feb 14, 2021 11:43 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Internal Energy, When Q is zero?
- Replies: 4
- Views: 301
Re: Internal Energy, When Q is zero?
Hi! I believe that all of your statements are correct. When q is zero, that definitely means that no heat is being transferred.
- Sun Feb 14, 2021 11:39 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Kelvin conversion
- Replies: 40
- Views: 2897
Re: Kelvin conversion
You add 273 to any Celsius temperature to get the temperature in Kelvin. For example, 25 C + 273 = 298 K.
- Sun Feb 14, 2021 11:37 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated System
- Replies: 6
- Views: 324
Re: Isolated System
Isolated systems are incredibly hard to obtain because there will almost always be some form of energy or matter exchange between the system and the surroundings. However, we can study systems that are extremely close to be pure isolated systems. Isolated systems are important to study because they ...
- Sun Feb 14, 2021 11:31 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Units for Gibbs Free Energy Calculations
- Replies: 6
- Views: 368
Re: Units for Gibbs Free Energy Calculations
G is typically answered in kJ, and H is usually given in kJ. However, S is usually given in J/K instead of kJ/K, so be sure to convert the J to kJ before plugging it into the equation. Hope this helps!
- Sun Feb 14, 2021 9:05 pm
- Forum: Ideal Gases
- Topic: Chem BL
- Replies: 107
- Views: 7139
Re: Chem BL
I am planning on taking 14BL next quarter so that I flow right from 14B into 14BL. I've heard it's good to take over the summer as well!
- Sun Feb 14, 2021 9:03 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: What are the three ways to find Delta H?
- Replies: 7
- Views: 12326
Re: What are the three ways to find Delta H?
Hi! I remember Dr. Lavelle stating that some of these are more reliable than the others, and I was wondering which ones are more accurate and why. Thank you! Hi! Out of the three methods (Hess's Law, Bond Enthalpies, and Standard Enthalpies of Formation), using bond enthalpies is the least accurate...
- Sun Feb 07, 2021 11:57 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Study Approach thermodynamics
- Replies: 8
- Views: 377
Re: Study Approach thermodynamics
My strategy is to work through a lot of textbook problems that use different formulas and set-ups. There are so many different equations, variables, and units used in this section that I think working through actual examples is going to be the best way to learn them all.
- Sun Feb 07, 2021 11:50 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work
- Replies: 39
- Views: 1395
Re: Work
Yes, -344 J is more work than -122 J because the system has lost more energy by doing work on its surroundings. A larger negative means more work done to the surroundings. You can use the absolute value of the J of work to compare how much work is being done if it's more helpful to think of it in po...
- Sun Feb 07, 2021 11:47 pm
- Forum: Student Social/Study Group
- Topic: Post Midterm 1...
- Replies: 39
- Views: 1586
Re: Post Midterm 1...
I am really going to focus on doing the textbook problems leading up to this next midterm, as I feel like not doing all of those messed me up on Midterm 1. I'm also going to review Midterm 1 with my TA to try and fix my mistakes for the final. Other than that, I'll be attending Justin's UA sessions,...
- Sun Feb 07, 2021 11:45 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sapling week 3&4 #14
- Replies: 3
- Views: 222
Re: Sapling week 3&4 #14
Hi! So the steps you commented about knowing how to do (using the PV=nRT and w=-nRTln(Vf/Vi) will give you your answer for part A. Then, for part B, the process occurs in two steps, so the work done by path B is a sum of the work in each step. The work done in these steps is calculated using w=-P(de...
- Sun Feb 07, 2021 6:21 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: using the q=mC(Tfinal - Tinitial) formula
- Replies: 4
- Views: 301
Re: using the q=mC(Tfinal - Tinitial) formula
Hopefully I'm not misunderstanding your question, but I substituted both T finals for x and then just solved for x algebraically by distributing. I think it might be easier for you to set the problem as one equation instead of multiple. This is how I did it: heat to melt ice + heat to warm melted i...
- Sun Jan 31, 2021 1:52 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Exothermic vs Extothermic
- Replies: 13
- Views: 405
Re: Exothermic vs Extothermic
Exothermic reactions release energy into their surroundings, which causes their environment to heat up. Endothermic reactions require energy, so they absorb it from their environment, thus causing their surroundings to get colder. I hope this helps!
- Sun Jan 31, 2021 1:50 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Exothermic Determined
- Replies: 6
- Views: 336
Re: Exothermic Determined
Kaleb Tuliau 3E wrote:So going from Cl2 to 2Cl would be endothermic?
Yes, this would be endothermic. The only bond change occurring is that a bond is being broken, which requires energy, thus making it endothermic.
- Sun Jan 31, 2021 1:43 pm
- Forum: Administrative Questions and Class Announcements
- Topic: midterm
- Replies: 16
- Views: 530
Re: midterm
I'd expect the scores to be posted in about a week. In 14A, Dr. Lavelle usually checked in about the midterm during the week and announced the average, and the scores were posted soon after that.
- Sun Jan 31, 2021 1:40 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: sapling week 3 and 4
- Replies: 9
- Views: 477
Re: sapling week 3 and 4
So we create our own numbers in consideration of the size/amounts? When I was doing the problem, I did use my own stand-in numbers to help me visualize and calculate the theoretical delta H. Just make sure that your numbers line up with the order of the strongest to weakest bonds present in the pro...
- Sun Jan 31, 2021 1:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K vs. Kc
- Replies: 36
- Views: 1215
Re: K vs. Kc
K and Kc are essentially the same thing; both are the equilibrium constants for reactions, but K is more of an umbrella term, whereas Kc is specifically an equilibrium constant that is calculated using concentrations.
- Sun Jan 24, 2021 1:16 pm
- Forum: Student Social/Study Group
- Topic: Midterm
- Replies: 21
- Views: 805
Re: Midterm
Our first midterm last quarter was about 12 questions, I believe. I wouldn't be surprised if this first exam was about the same length. Hope this helps!
- Sun Jan 24, 2021 1:13 pm
- Forum: Phase Changes & Related Calculations
- Topic: Steam
- Replies: 33
- Views: 1805
Re: Steam
The steam causes more severe burns because of the large amount of energy it takes to turn liquid water into steam. If you think about the steam as condensing when it hits your skin, then the steam must release all the energy it took to phase change into vapor, and therefore it releases a lot of heat...
- Sun Jan 24, 2021 1:09 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm Timing
- Replies: 15
- Views: 404
Re: Midterm Timing
I found the first midterm in Chem 14A to have plenty of time, but midterm 2 and particularly the final were definitely time crunches. As other commenters have said, Dr. Lavelle usually tells us the number of questions on the exams beforehand, which is helpful to plan for timing. I wouldn't worry too...
- Sun Jan 24, 2021 12:54 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Units for Standard Reaction Enthalpy
- Replies: 3
- Views: 100
Re: Units for Standard Reaction Enthalpy
I always thought that the "per mole" in the unit for enthalpy was implied, similarly to how the number of atoms per mole being Avagadro's number was implied as being "per mole". Therefore, I'd assume that the kJ and kJ/mol would mean the same thing, and would only be written with...
- Sun Jan 24, 2021 12:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling Homework #7
- Replies: 10
- Views: 311
Re: Sapling Homework #7
705512695 wrote:This was very helpful but I just have a question when you say you ignored the "-x" how do you know when to ignore it? How small does Kb have to be ?
I believe the rule is that if the Kb is smaller than 10^-4, then you know that the changes will be small enough to ignore.
- Fri Jan 22, 2021 7:45 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: bonds broken and formed for bond enthalpy method [ENDORSED]
- Replies: 2
- Views: 56
Re: bonds broken and formed for bond enthalpy method [ENDORSED]
Hi! I find it helpful to write out the balanced equation first, and then, if needed, to draw the Lewis structures for the molecules involved on each side. The bonds broken will be all the bonds in the molecules on the left/reactants side of the equation, and the bonds formed will be all of those in ...
- Sat Jan 16, 2021 7:33 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Identifying Acids, Bases, and salts
- Replies: 8
- Views: 442
Re: Identifying Acids, Bases, and salts
Hi! For help on determining whether a molecule is an acid or a base, here are some tips. An acid will contain an H atom somewhere in its formula that it can lose to form H3O+ when combined with water. For example, when combined with H2O, H2SO4 can lose an H to form HSO4- and H3O+. Other acids that f...
- Fri Jan 15, 2021 7:34 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Gas
- Replies: 16
- Views: 574
Re: Gas
Typically, the units of the gas will be given in the equation. Bar is the SI unit for gas, so if it does not say a unit, it may be safe to assume that the gas is measured in bar. However, atm and bar are so close that the professor said we can typically trade them out without consequence.
- Fri Jan 15, 2021 7:31 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: q and K
- Replies: 11
- Views: 289
Re: q and K
The difference between Q and K is that K is only measured at equilibrium, and, if the reaction quotient is calculated at any other point during the reaction, it is called Q. K can come at different temperatures, because equilibrium occurs at different temperatures, but K will vary from temperature t...
- Fri Jan 15, 2021 7:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: When x is negligible in Equilibrium constant
- Replies: 34
- Views: 1382
Re: When x is negligible in Equilibrium constant
Dr. Lavelle said that x must be smaller than 10^-3, but, to be safe, you should make sure that x is significantly smaller than the molar concentrations- as other commenters have said, 5% is a really good benchmark to use (because 10^-3, in some situations, could be large enough to not be negligible).
- Fri Jan 15, 2021 7:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Strong Acid and Base
- Replies: 4
- Views: 234
Re: Strong Acid and Base
Hi! As the commenter above said, the H+ or OH- comes from the dissociation of the strong acid or the strong base. Just like the dissociation of NaCl in water would cause both Na+ and Cl- ions to form, when a strong acid like HCl dissociates in water, both H+ and Cl- ions are formed, so H+ has a mola...
- Fri Jan 15, 2021 7:17 pm
- Forum: Ideal Gases
- Topic: Units of Temperature
- Replies: 82
- Views: 3356
Re: Units of Temperature
We should use Kelvin for all of chemistry. Many temperatures will be given in Celsius, so to convert from Celsius to Kelvin, you add 273 to the Celsius temperature.
- Sun Jan 10, 2021 10:50 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: sapling week 1 #9
- Replies: 15
- Views: 678
Re: sapling week 1 #9
Taylor Newville 1C wrote:You can use either K or 1/K for this question and get the same answer. If you use K, make sure you set it equal to [NO]^2/[N2][O2]. And if you use 1/K, make sure you set it equal to [N2][O2]/[NO]^2.
Thank you so much! I'll try again, this time with 1/K, and hopefully it'll work.
- Sun Jan 10, 2021 10:47 pm
- Forum: Student Social/Study Group
- Topic: Favorite TV shows
- Replies: 277
- Views: 34354
Re: Favorite TV shows
Some of my favorite TV shows at the moment are Schitt's Creek and Community (which are both on Netflix) and Psych (which is on Amazon Prime)! Also, if you're into history, Band of Brothers is a really great miniseries about a troop throughout World War 2, and that is also on Amazon Prime. I'll defin...
- Sun Jan 10, 2021 10:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling System of Equations
- Replies: 2
- Views: 97
Re: Sapling System of Equations
Hi! For this problem, you only need to include equations that involve the reactants and products in some way. If there is a reaction mechanism that does not include the products and reactants, it will not be useful for you, so you can disregard it. For my problem, I only used two of the intermediate...
- Sun Jan 10, 2021 10:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling #3
- Replies: 4
- Views: 174
Re: Sapling #3
Hi! Can you post the specific reaction that you have for question #3? That would make it easier to describe and help you!
- Sun Jan 10, 2021 10:36 pm
- Forum: Ideal Gases
- Topic: Pressure and partial pressure
- Replies: 12
- Views: 426
Re: Pressure and partial pressure
Hi! The total pressure is the combined pressure of all of the gases in the mixture within the vessel. The partial pressure of each gas is the portion of this pressure associated with each gas in the mixture. So, if the partial pressure of one gas was 0.75 atm, and another gas had a partial pressure ...
- Sun Jan 10, 2021 5:08 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling hw 5
- Replies: 14
- Views: 490
Re: Sapling hw 5
Hi! You want to pick only the equations that allow you to end up at the overall reaction at the top. Therefore, you only need the equations involving the products and/or reactants of the overall reaction in some form. For example, in this problem, you would not need to use the reaction with Kd at al...
- Sun Jan 10, 2021 4:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: sapling week 1 #9
- Replies: 15
- Views: 678
Re: sapling week 1 #9
Hi! I'm really struggling on this question. I swear I've followed all the correct steps, and I've redone the problem completely just to double check, and somehow I just keep coming up with the wrong answer. Just to clarify, as I have seen it both ways on here: should I be setting the new Kc equation...
- Wed Dec 16, 2020 1:36 pm
- Forum: Student Social/Study Group
- Topic: Curve
- Replies: 33
- Views: 2247
Re: Curve
There is definitely no curve in terms of a 'bell curve', which I am very grateful for. As the other commenters have said, though, he did kind of 'curve' our final by adding points.
- Wed Dec 16, 2020 1:34 pm
- Forum: Conjugate Acids & Bases
- Topic: Strong acid / base conjugates
- Replies: 3
- Views: 300
Re: Strong acid / base conjugates
No, which is why strong acids have extremely weak conjugate bases and strong bases have very weak conjugate acids. It is very difficult for conjugate bases of strong acids to accept a proton or donate a lone pair because of the high dissociation of the strong acid.
- Wed Dec 16, 2020 1:32 pm
- Forum: *Indicators
- Topic: Which indicator?
- Replies: 2
- Views: 746
Re: Which indicator?
I would say that an indicator with a smaller range that includes the predicted pH would be the best to use. I assume that because the range is more narrow, it would be easier to find if the predicted pH really does fall into that range. Like Gwendolyn said, though, it would also be good to run the e...
- Wed Dec 16, 2020 1:26 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Strong acid / base ion
- Replies: 8
- Views: 406
Re: Strong acid / base ion
Yes, the ions in the strong acids and bases will completely dissociate and the pH of the end solution will be neutral. As Brandon said, you can basically think of it as the two cancelling each other out.
- Wed Dec 16, 2020 1:22 pm
- Forum: Student Social/Study Group
- Topic: Winter Break
- Replies: 44
- Views: 2035
Re: Winter Break
I might rewatch the video modules from some of the earlier concepts in 14A because I feel like I won't retain that information as well since we learned it a while ago (although, knowing me, I'll likely forget to do that). Other than that, I'll probably just keep my 14A notebook handy as we start 14B.
- Sun Dec 13, 2020 2:12 am
- Forum: Student Social/Study Group
- Topic: Upcoming Finals
- Replies: 7
- Views: 505
Re: Upcoming Finals
Well, you can see from my post time that I'm not doing too well on the "get some sleep" thing... oops! I really appreciate these words of encouragement, Aliya! Good luck everyone. We've got this!
- Sun Dec 13, 2020 2:09 am
- Forum: Bronsted Acids & Bases
- Topic: Fundamentals J #9b
- Replies: 2
- Views: 165
Re: Fundamentals J #9b
I assumed that the reason for writing out the dissociated version of H3PO4 was to see where the H+ goes when it becomes a product- basically, to help us visualize it better. However, looking at it now, I see that the H+ transfers from HBrO2 to H2O in part (c), but the HBrO2 is not written out in a w...
- Sun Dec 13, 2020 2:03 am
- Forum: Bronsted Acids & Bases
- Topic: Strong bases oxides vs hydroxides
- Replies: 4
- Views: 578
Re: Strong bases oxides vs hydroxides
I believe that the more moles of OH- produced, the stronger a base will be. I remember that being alluded to on the Sapling for this week; when we had to order bases in order of strength, it told me that the more OH- produced, the stronger of a base it is. Therefore, I think you're right in saying t...
- Sun Dec 06, 2020 1:26 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Determining Oxidation Numbers
- Replies: 4
- Views: 97
Re: Determining Oxidation Numbers
I do think it's best to know oxidation numbers of common atoms and the overall way of assigning them, simply because it will make answering questions involving oxidation numbers a lot faster. Some key oxidation number trends to remember are that elements in the first column of the periodic table hav...
- Sun Dec 06, 2020 1:18 am
- Forum: Student Social/Study Group
- Topic: Studying for Final Exam
- Replies: 57
- Views: 2433
Re: Studying for Final Exam
Hi! I also tend to lack organization while studying, so I'm going to attend lots of review sessions for this final so that the studying is structured for me! I also plan on completing all the textbook questions before the final, which is a lot of work, but has proven to be worth it on the two midter...
- Sun Dec 06, 2020 1:14 am
- Forum: Student Social/Study Group
- Topic: How are you?
- Replies: 154
- Views: 12370
Re: How are you?
I can't believe it's the end of Week 9. I feel like the quarter has flown by. I'm hoping for the best for this last week of class and for the final. Good luck everyone! Hope you're doing alright!
- Sun Dec 06, 2020 1:08 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Sapling W9 #3
- Replies: 6
- Views: 320
Re: Sapling W9 #3
If you think about it, the points on a hexagon are much closer to each other than the points on a three-dimensional figure with 6 vertices (I can't remember what that shape is called) Just to clarify this, this shape for a molecule with six bonded atoms is an octahedral structure. To add on to what...
- Sun Dec 06, 2020 1:01 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: ligands
- Replies: 11
- Views: 438
Re: ligands
NH3 is a neutral molecule on its own; therefore, it acts as a neutral ligand. I had this same question, and I found that drawing out the Lewis structure and calculating the formal charge on each atom (which will all be 0) to be helpful in determining an answer, as it made it easy to see that NH3 has...
- Sun Nov 29, 2020 10:01 pm
- Forum: Student Social/Study Group
- Topic: Tips for Staying Focused
- Replies: 64
- Views: 3579
Re: Tips for Staying Focused
One of the few focusing tips that I have is to drink lots of water as you're studying. A lot of times when we are feeling sleepy or cloudy-headed, it is because we are dehydrated, so drinking water can help you wake up/stay alert! Plus, getting up to go to the bathroom after you drink a ton of water...
- Sun Nov 29, 2020 9:57 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: AsO43-
- Replies: 9
- Views: 424
Re: AsO43-
AsO43- has a symmetric distribution of O around the central As, and all four atoms surrounding As are the same and thus will have the same electronegativity (and the same dipole moment with As). Therefore, the dipole moments between the As and each O will cancel out. Drawing the dipole arrows on the...
- Sun Nov 29, 2020 9:53 pm
- Forum: Electronegativity
- Topic: Be vs Cl
- Replies: 49
- Views: 2669
Re: Be vs Cl
Hi Karina! I look at this when looking at electronegativity: Cl is much further right on the periodic table than Be, but Be is only one row higher than Cl. Therefore, it makes sense that Cl has a higher electronegativity than Be. Hope this helps!
- Sun Nov 29, 2020 9:48 pm
- Forum: Student Social/Study Group
- Topic: Final Exam Partial Credit
- Replies: 1
- Views: 167
Re: Final Exam Partial Credit
Hi Claire! I'm not sure if Dr. Lavelle has said whether or not there will be partial credit for the final yet. I'll ask my TA during my discussion this week. This also would be a good question to ask at Dr. Lavelle's office hours. I hope we can get the answer to this soon!
- Sun Nov 29, 2020 9:45 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: sigma vs pi bonds
- Replies: 33
- Views: 1989
Re: sigma vs pi bonds
Single bonds are sigma bonds. Double bonds contain a pi and a sigma bond, and a triple bond has one sigma and two pi bonds. Therefore, all three contain sigma bonds. Something that helps me remember the number of pi bonds in a bond type is that for double and triple bonds, the number of pi bonds is ...
- Sun Nov 29, 2020 9:38 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: London Dispersion
- Replies: 33
- Views: 1686
Re: London Dispersion
what determines how strong london dispersion forces are again? Large, heavy atoms have stronger London Dispersion forces than smaller, lighter atoms because they are more polarizable and have more electrons. On a related note, the larger the surface area of an atom, the stronger its London Dispersi...
- Sat Nov 21, 2020 7:52 pm
- Forum: Ionic & Covalent Bonds
- Topic: Covalent Character
- Replies: 33
- Views: 1432
Re: Covalent Character
As other commenters have mentioned, looking at the difference in electronegativity is a great way to determine covalent vs. ionic character. I'd also like to point out that highly polarizable ions that are large and rich in electrons (such as I-) lead to more covalent bond character, which is why th...
- Sat Nov 21, 2020 7:45 pm
- Forum: Ionic & Covalent Bonds
- Topic: Polar Bonds [ENDORSED]
- Replies: 26
- Views: 1212
Re: Polar Bonds [ENDORSED]
If a molecule has a symmetric structure with all the same atoms around the central atom (for example, SF6), you can immediately tell that the molecule is non-polar, With molecules that have an asymmetric structure, you can look at the atoms within the molecule and use periodic trends to help you det...
- Sat Nov 21, 2020 7:37 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron configuration exceptions
- Replies: 7
- Views: 1585
Re: Electron configuration exceptions
Ni should be written [Ar] 3d8 4s2 and not [Ar] 3d10. The reason that Cu and Cr are exceptions is that they are only 1 electron away from filling the d-orbital, and thus it makes them more stable to fill up that one electron in the d-orbital rather than the s-orbital. However, I strongly believe that...
- Sat Nov 21, 2020 6:17 pm
- Forum: Student Social/Study Group
- Topic: Post Midterm Blues
- Replies: 71
- Views: 3214
Re: Post Midterm Blues
I definitely realized some mistakes I made right after I submitted my midterm, but hopefully what we learn from this midterm's mistakes will help us succeed on the final (fingers crossed!).
- Sat Nov 21, 2020 6:13 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Charge of a Molecule / Distribution of Charge
- Replies: 5
- Views: 322
Re: Charge of a Molecule / Distribution of Charge
The positive and negative identifiers that Dr. Lavelle used in his lectures for charge distribution seemed to be based more off of the electronegativity of an atom than the formal charges found in Lewis structures. For example, in KCl, Cl would carry the partial negative charge because it has a high...
- Sun Nov 15, 2020 10:58 pm
- Forum: Octet Exceptions
- Topic: octet rule exceptions
- Replies: 6
- Views: 185
Re: octet rule exceptions
Hydrogen is an exception to the octet rule, as it only needs 2 electrons to be satisfied. Atoms in the 3rd row of the periodic table and below can sometimes take on extra electrons and therefore exceed the octet rule. I read this in the textbook, but wasn't sure if it mean only p-block elements bel...
- Sun Nov 15, 2020 10:56 pm
- Forum: Lewis Structures
- Topic: Sapling Week 5/6 HW #3
- Replies: 7
- Views: 212
Re: Sapling Week 5/6 HW #3
Hi! My TA said that because we have not gotten to the naming section of this class yet, we should not be expected to know the names of the various ions for this midterm, but we will likely need to know it for the final. However, as the other commenters have said, it definitely wouldn't hurt to revie...
- Sun Nov 15, 2020 10:53 pm
- Forum: Bond Lengths & Energies
- Topic: Hydrogen Bond Length
- Replies: 3
- Views: 79
Re: Hydrogen Bond Length
The bonds do not have to be the same length because the bond length is dependent on whether H is bonding with N, O, or F. From a table on chemistryreference.com, I found that the typical H-F bond length is 92 pm, whereas O-H is 96 pm and N-H is 101 pm. Therefore, I believe that even if two molecules...
- Sun Nov 15, 2020 10:45 pm
- Forum: Lewis Structures
- Topic: Lewis Acids and Bases VS Cations and Anions
- Replies: 3
- Views: 258
Re: Lewis Acids and Bases VS Cations and Anions
From Dr. Lavelle's lecture, it seemed like Lewis Acids and Lewis Bases are different from cations and anions. For example, BF3 was considered a Lewis acid, but it does not have a positive or negative charge, so it is not a cation or anion. I believe the important distinction to make is that cations ...
- Sun Nov 15, 2020 10:42 pm
- Forum: Bond Lengths & Energies
- Topic: Sapling Question 11
- Replies: 5
- Views: 1206
Re: Sapling Question 11
H is a smaller atom than O, which means that the bond between it and N will be shorter. In addition, there is a higher difference in electronegativity between N and H than N and O, which means that N and H will pull closer together.
- Sun Nov 15, 2020 10:39 pm
- Forum: Ionic & Covalent Bonds
- Topic: London (Dispersion) Force
- Replies: 3
- Views: 170
Re: London (Dispersion) Force
Hi! In addition to the size of the atoms, the size of the overall molecule will affect the LDF; the larger the molecule, the stronger the LDF. This typically means that molecules with longer chains of atoms will have stronger London Dispersion Forces than molecules with shorter chains. In addition, ...
- Sun Nov 15, 2020 10:35 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 3d and 4s orbitals
- Replies: 4
- Views: 1211
Re: 3d and 4s orbitals
I believe that in our class, we will write 3d before 4s in all circumstances. As a previous commenter pointed out, it is important to remember that the 4s orbital should always be filled before the 3d, even though the 3d orbital is written first. The 3d and 4s orbitals are very close in energy, whic...
- Mon Nov 09, 2020 1:02 am
- Forum: Octet Exceptions
- Topic: octet rule exceptions
- Replies: 6
- Views: 185
Re: octet rule exceptions
Hydrogen is an exception to the octet rule, as it only needs 2 electrons to be satisfied. Boron is another exception that can have less than 8 electrons around it (typically, it works with 6 electrons). Beryllium can also be satisfied with less than 8. Atoms in the 3rd row of the periodic table and ...
- Mon Nov 09, 2020 12:53 am
- Forum: Ionic & Covalent Bonds
- Topic: resources
- Replies: 7
- Views: 129
Re: resources
Hi! I really enjoy Crash Course videos on YouTube. Here's the link for a playlist with a ton of their chemistry videos: https://www.youtube.com/watch?v=uVFCOfS ... aX9mQQ8oGr.
- Mon Nov 09, 2020 12:46 am
- Forum: Lewis Structures
- Topic: Resonance structure
- Replies: 3
- Views: 74
Re: Resonance structure
Hi! A molecule with resonance structures has more than one valid Lewis structure that can represent that molecule. For example, NO3-, the nitrate ion, has 3 valid structures that can represent it. These are called the resonance structures. The resonance hybrid can be thought of as the average of the...
- Mon Nov 09, 2020 12:38 am
- Forum: Lewis Structures
- Topic: Lewis Structure Drawing
- Replies: 2
- Views: 89
Re: Lewis Structure Drawing
Hi! Most atoms want to have 8 electrons attached to them in some ways, either through lone pairs of electrons on the atom or through bonds, in order to get a full octet. There are some exceptions, such as H, which needs only 2 electrons. Single bonds (one line) mean 2 electrons are being shared, dou...
- Mon Nov 09, 2020 12:24 am
- Forum: Trends in The Periodic Table
- Topic: Atomic radius
- Replies: 4
- Views: 226
Re: Atomic radius
Hi! I would guess that we would use the periodic trend concerning atomic radii to determine which atom has the larger radius. It seems that the atomic radii trend tends to be very consistent across the periodic table, which would probably make it easier to use than looking at the number of valence e...
- Fri Oct 30, 2020 6:41 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Units for Uncertainty in Position
- Replies: 6
- Views: 183
Re: Units for Uncertainty in Position
Mathematically, the units of uncertainty in position must be meters in order for the other units in the Heisenberg equation to cancel out correctly while you are solving for a value. Conceptually, the reason that m is to the first power and is not m^3 is because we assume that the electron's possibl...
- Thu Oct 29, 2020 12:32 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Sapling HW #11
- Replies: 2
- Views: 99
Re: Sapling HW #11
Hi Marco! I didn't have this exact question, but the steps should be the same from the one I had. Step 1: Find the frequency that corresponds to 434.0 nm by using v=c/wavelength. (Remember to convert the wavelength from nm to m.) Step 2: Using the Rydberg equation, plug the calculated frequency in f...
- Thu Oct 29, 2020 12:19 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Rydberg Equation
- Replies: 9
- Views: 283
Re: Rydberg Equation
n2 represents the excited state the electron is in, while n1 represents the energy level that the electron returns to. n2 is always greater than n1. I may be wrong, but that's the way I think about the Rydberg Equation. Thank you so much for this explanation! I have been confused about what n1 and ...
- Wed Oct 28, 2020 1:06 am
- Forum: Properties of Light
- Topic: rydberg's constant
- Replies: 11
- Views: 900
Re: rydberg's constant
Hi! The 3.29e15 Hz is the version of the Rydberg constant that is on Dr. Lavelle's Constants and Equations sheet, so I'd say that at least for now, that is definitely the more convenient/recommended version of the constant to use for this class. It is also the constant that I assume works with the v...
- Tue Oct 27, 2020 12:00 am
- Forum: Properties of Light
- Topic: increasing intensity
- Replies: 5
- Views: 212
Re: increasing intensity
I think that the reason that it is not outright false is because in a traditional wave model, increasing the intensity (amplitude) would result in an increase in energy. It's like the analogy Dr. Lavelle gave of standing in the ocean and being hit by a 2-foot wave versus a 10-foot wave. Even at the ...
- Sun Oct 25, 2020 5:08 pm
- Forum: SI Units, Unit Conversions
- Topic: Textbook Practice Problem Answers
- Replies: 4
- Views: 191
Re: Textbook Practice Problem Answers
Hi! This happens to me quite frequently, too. Sometimes, the big numbers with scientific notation just don't load in the answer key. I know that Sachi has already provided the answer key PDF, which is awesome; I just wanted to add this for anyone else who has this issue, because I don't think the lo...
- Sun Oct 25, 2020 5:02 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Clarification on the "uncertainty" part of this equation
- Replies: 7
- Views: 362
Re: Clarification on the "uncertainty" part of this equation
The main takeaway from the Heisenberg Indeterminacy Equation is that we can never measure an electron's exact momentum and position because, by measuring these values, we change them. Therefore, there is always some element of uncertainty in an electron's measured position and momentum. Heisenberg's...
- Sun Oct 25, 2020 4:50 pm
- Forum: Photoelectric Effect
- Topic: Calculations
- Replies: 18
- Views: 592
Re: Calculations
I always try to keep all the digits throughout the calculation to the best of my ability, but I know that on a previous post on Chem Community, Dr. Lavelle said that a little bit of rounding is okay- for example, if the final answer has 2 sig figs, then it's okay to only keep 4 sig figs throughout y...
- Sun Oct 25, 2020 1:48 pm
- Forum: Significant Figures
- Topic: Midterm
- Replies: 9
- Views: 512
Re: Midterm
On the practice quiz that I did with my TA, there was a question that had us choose between two answers with different sig figs, but that doesn’t necessarily mean a question like that will be on the midterm. If the other commenters’ TA’s have said that sig figs won’t be on the midterm, I’d go with t...
- Sun Oct 25, 2020 10:44 am
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Question about the Delta X and what it stands for
- Replies: 6
- Views: 500
Re: Question about the Delta X and what it stands for
Hi! To echo what the other commenters have said, delta X stands for the uncertainty in position. There are many different ways this uncertainty can be shown. If the diameter of the electron's "container" is given, then that will be the uncertainty in position. For example, in a problem tha...
- Sun Oct 18, 2020 2:05 am
- Forum: Student Social/Study Group
- Topic: How do you study?
- Replies: 19
- Views: 639
Re: How do you study?
Hi Nicolette! I'm also a freshman, and definitely having trouble adjusting to the online college set up/workload. I wanted to pass along some study advice I got from my New Student Mentor, which I am trying to put into practice myself. My mentor suggested starting homework as soon as you are done wa...
- Sun Oct 18, 2020 1:47 am
- Forum: Significant Figures
- Topic: When should I start looking at sig figs?
- Replies: 31
- Views: 1394
Re: When should I start looking at sig figs?
Hi! As many other commenters under this post have said, I think it is best to try and keep as many places after the decimal as possible while you are doing your work, and then round for sig figs only at the end. However, I also saw a post by Dr. Lavelle on Chem Community about how many digits to kee...