Search found 123 matches
- Thu Mar 11, 2021 5:15 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Potentials as State Functions
- Replies: 1
- Views: 124
Cell Potentials as State Functions
There has been conversation in multiple review sessions about whether E/E0 are state functions. Some people are saying that are for redox reactions so you can add E0 values together, but if the reaction is not a redox then you have not to convert E0 to deltaG0, add those to values together and then ...
- Wed Mar 10, 2021 11:31 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Units for Activation Energy
- Replies: 28
- Views: 1854
Units for Activation Energy
What are the units for activation energy?
- Wed Mar 10, 2021 11:21 pm
- Forum: General Rate Laws
- Topic: Matthew's Week 10 WS Question
- Replies: 1
- Views: 163
Matthew's Week 10 WS Question
Hey guys.
I was wondering if anybody who went to Matthew's workshop could explain how they found the rate law and the value of the rate constant. Thanks :)
I was wondering if anybody who went to Matthew's workshop could explain how they found the rate law and the value of the rate constant. Thanks :)
- Tue Mar 09, 2021 10:42 am
- Forum: Balancing Redox Reactions
- Topic: Reducing/Oxidizing/ Reducing Agents / Oxidizing Agents
- Replies: 1
- Views: 132
Reducing/Oxidizing/ Reducing Agents / Oxidizing Agents
Hey everyone! I'm a little bit confused about the wording around some of these terms. I just wanted some confirmation. Reducing Agent: Does the reducing so is being oxidized by giving up electrons Oxidizing Agent: Does the oxidizing so is being reduced and readily accepts electrons Reducing Metal: ?...
- Sun Mar 07, 2021 8:07 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Textbook Question 6L.3
- Replies: 2
- Views: 167
Textbook Question 6L.3
Hey guys, I was wondering how you guys went about solving these questions. I'm having a hard time reading the diagrams and understanding how to derive the half reactions from them. Also, the answer question was mentioning flipping reactions for anodes, and I don't really understand that part either....
- Sun Mar 07, 2021 1:06 am
- Forum: Administrative Questions and Class Announcements
- Topic: Sapling Not Working??
- Replies: 7
- Views: 407
Re: Sapling Not Working??
UPDATE: it's working now!
- Sat Mar 06, 2021 9:23 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Sapling Not Working??
- Replies: 7
- Views: 407
Sapling Not Working??
Hi everyone! I'm currently trying to do the week 9/10 homework but it's not loading. There's an error message about network problems and stuff. I was able to log in originally and do like the first 3 problems but when I clicked to go to the next one, it pooped out and said something about network er...
- Sat Mar 06, 2021 12:03 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cathode in Diagrams
- Replies: 6
- Views: 365
Cathode in Diagrams
I just wanted to confirm that the cathode is always on the right side of a diagram. I believe in the textbook it said that if the cell potential is negative, that the cathode is on the left. Can someone please confirm this detail? :) Thanks!
- Fri Mar 05, 2021 1:07 pm
- Forum: First Order Reactions
- Topic: Order Graphs
- Replies: 8
- Views: 433
Order Graphs
I am a little bit confused about how to use the graphs. Are we ever going to have to graph the rate plots or will they be given to us? Also, if we are suppose to graph them ourselves, is kind of like trial and error. So for example, you graph ln[A] vs time and it does NOT give you a straight line, t...
- Wed Mar 03, 2021 2:29 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Order part II
- Replies: 3
- Views: 250
Order part II
Hey all, I feel like I missed a massive chunk of the kinetic sections when it comes to order. I had a previous post about what order it. If a reaction has 1 reactant, that makes it a first-order? If it has two does that make it a second-order? How do we determine if a reaction is dependent upon 1 re...
- Mon Mar 01, 2021 1:57 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: First - Order/Order
- Replies: 10
- Views: 502
First - Order/Order
Can someone PLEASE explain what is meant by "order" in this unit. What is meant by first-order, second-order, etc? Thank you :)
- Mon Mar 01, 2021 1:55 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: First - Order/Order
- Replies: 7
- Views: 430
First - Order/Order
Can someone PLEASE explain what is meant by "order" in this unit. What is meant by first-order, second-order, etc? Thank you :)
- Sat Feb 27, 2021 7:49 pm
- Forum: Balancing Redox Reactions
- Topic: Monoatomic Ions
- Replies: 2
- Views: 217
Monoatomic Ions
In sapling question 1, the solution says that K in both KClO4 and KCl is a monoatomic ion, but Cl is only a monoatomic ion in KCl and not in KClO4. I was wondering why that is?
- Sat Feb 27, 2021 7:44 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Concentration Cell
- Replies: 1
- Views: 122
Concentration Cell
In the Applications lecture, Lavelle went over this example of 0.1M of Ag+ being in 0.1M NO3 - separated by a porous disc with 1M Ag+ in 1M of NO3-. He had mentioned that the concentration of Ag one the 0.1M side would begin to increase but I was wondering how that would be. Is the porous disc open ...
- Sat Feb 27, 2021 7:39 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Sapling Question #7
- Replies: 4
- Views: 1837
Re: Sapling Question #7
The shorthand is done based on what comes in contact with what first. So for this one, the shorthand is Pb l PbCl2 l Cl- ll Cl- l AgCl l Ag. The anode is on the left and the cathode is on the right.
- Sat Feb 27, 2021 7:36 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Standard Hydrogen Electrode
- Replies: 3
- Views: 215
Standard Hydrogen Electrode
Can someone explain why the S.H.E has an Enaught value of 0, please? Thanks!
- Sat Feb 27, 2021 5:23 pm
- Forum: Balancing Redox Reactions
- Topic: Sapling Week 7/8 - Question #5
- Replies: 3
- Views: 231
Sapling Week 7/8 - Question #5
Hey everyone!
I've seen this problem a lot on Chemistry Community and I've followed everyone's instructions and I'm still getting the wrong answer. I'm on my 11th attempt, so if anyone can tell me what's up, I would very much appreciate it!
I've seen this problem a lot on Chemistry Community and I've followed everyone's instructions and I'm still getting the wrong answer. I'm on my 11th attempt, so if anyone can tell me what's up, I would very much appreciate it!
- Thu Feb 18, 2021 10:15 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4D9 Explanation
- Replies: 1
- Views: 121
Re: 4D9 Explanation
Hello! This question was kinda tricky. To begin, you use the enthalpies of formation to get the total enthalpy for the reaction. Then you have to take 1/4 of that to find the enthalpy for the TNT, which is done because there is 4 moles. This is the amount of energy released by the reaction as the TN...
- Wed Feb 17, 2021 11:40 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Order and Stability
- Replies: 4
- Views: 226
Re: Order and Stability
Stability is based on Gibbs free energy and not just entropy. For example, lets use the reaction A --> B + C. If the Gibbs free energy is negative, A is not stable: When Gibbs free energy is negative, the reaction is spontaneous. Therefore, A will turn into B and C without the help of an outside fo...
- Wed Feb 17, 2021 11:36 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Order and Stability
- Replies: 4
- Views: 226
Re: Order and Stability
Higher entropy means higher disorder and more possible arrangements. The entropy of gases > the entropy of liquids > the entropy of solids. However, when looking at whether a molecule is likely to form, we also need to take into account enthalpy and the temperature of the reaction to see if the for...
- Wed Feb 17, 2021 11:19 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Order and Stability
- Replies: 4
- Views: 226
Order and Stability
This is more of a confirmation question that I deduced while doing the textbook problems.
A more negative entropy means more disorder, which suggests less stability.
A more positive entropy means more order, which suggests more stability.
Please correct me if I'm wrong :). Thanks!
A more negative entropy means more disorder, which suggests less stability.
A more positive entropy means more order, which suggests more stability.
Please correct me if I'm wrong :). Thanks!
- Wed Feb 17, 2021 11:02 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Why are there fractional coefficients?
- Replies: 1
- Views: 203
Why are there fractional coefficients?
Hey everybody! I have a question about two types of problems. Question 4J.5 gives this problem and how I tend to solve this problem is to write a balanced equation and solve from there. However, the solution manual seems to have fractional coefficient and calculates the delta H/S per 1 mole when the...
- Wed Feb 17, 2021 9:44 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Textbook Question 4H.9
- Replies: 2
- Views: 226
Textbook Question 4H.9
Question: Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The conta...
- Tue Feb 16, 2021 12:38 pm
- Forum: Student Social/Study Group
- Topic: Students Who Have a Job
- Replies: 103
- Views: 8980
Re: Students Who Have a Job
Hey! I also have a part-time job. I work for UCLA IT Support Center and I work about 12 hours a week. The most important thing is to give yourself time to relax and decompress, especially with a class like Chem that is really stressful. I've started going on walks with my roommate and weekend hikes ...
- Sat Feb 13, 2021 5:52 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Homework Question #3
- Replies: 3
- Views: 147
Homework Question #3
Hey all! I was doing the homework yesterday and came across this problem. I was wondering if there were any situations that would fit into the middle two boxes. Thanks!
- Sat Feb 13, 2021 5:50 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Sapling question 4
- Replies: 9
- Views: 411
Re: Sapling question 4
Hello! First step is determining the right equation. The only thing that is mentioned here really is the volume change so the right equation would be delta S = nRlnV2/V1. You're indirectly given the moles as 1 and you know the R constant. For problems like these, I would recommend assigning random v...
- Sat Feb 13, 2021 5:42 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta S dominates vs delta H dominates
- Replies: 5
- Views: 278
delta S dominates vs delta H dominates
In class, we did that example of Br2 (l) --> Br2 (g). Part of the explanation said that when T > 333K that the delta S dominates but when T < 333K that delta H dominates. I was wondering if someone could explains what it means for these two terms to dominate? Thanks!
- Wed Feb 10, 2021 5:18 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy
- Replies: 5
- Views: 298
Gibbs Free Energy
This may be a dumb question, but what exactly does G represent? I know that, for example, q is heat and H is enthalpy, but I'm not sure how to summarize G inn a similar fashion. Thank you! :)
- Wed Feb 10, 2021 5:14 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Thermo Equilibrium like Chemical Equilibrium?
- Replies: 4
- Views: 229
Thermo Equilibrium like Chemical Equilibrium?
In class today, Dr. Lavelle mentioned that at thermo equilibrium there is no transfer of heat. I was wondering if this means no NET transfer of heat, but rather just an equal movement of heat (kinda like in chemical equilibrium, or no transfers of heat at all. Thanks!
- Wed Feb 10, 2021 5:11 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Thermo Equilibrium
- Replies: 4
- Views: 253
Thermo Equilibrium
Hello! Can someone explain what it means for a system to be at thermo equilibrium please? How can you tell if a system is at thermo equilibrium? Thank you!
- Fri Feb 05, 2021 10:51 pm
- Forum: Student Social/Study Group
- Topic: Study tips for thermo
- Replies: 14
- Views: 722
Re: Study tips for thermo
Hello! Something I find really helpful is really just going through the textbook and assigned readings. The textbook really breaks down the different equations, which is something I struggle with. Going through the example boxes and making sure you understand everything that is being done is super h...
- Fri Feb 05, 2021 4:48 pm
- Forum: Student Social/Study Group
- Topic: Any cool clubs?
- Replies: 12
- Views: 618
Any cool clubs?
Hey guys!
I was wondering if anybody knows or is a part of any cool clubs? I'm looking for some ways to keep busy for the time being. Feel free to drop any kind of club, thanks! :D
I was wondering if anybody knows or is a part of any cool clubs? I'm looking for some ways to keep busy for the time being. Feel free to drop any kind of club, thanks! :D
- Fri Feb 05, 2021 4:40 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: energy replaced by heat
- Replies: 3
- Views: 163
Re: energy replaced by heat
Based on the diagram he had at the beginning of the lecture, it looks like the heat comes from the surrounding. So the surroundings serve as a heat reservoir.
- Wed Feb 03, 2021 3:32 pm
- Forum: Phase Changes & Related Calculations
- Topic: Sapling #4 Question 10 - Temperature
- Replies: 19
- Views: 12484
Re: Sapling #4 Question 10 - Temperature
Hello! I think your setup would look a little something like this. Using the q = mCsdeltaT equation you can input the information that you know from both the ice cube and the water and set them equal to each other. (53.0g)(4.184 J/g*C)(Tf - 0C) = - (444g)(4.184 J/g*C)(Tf - 45C) You then multiple the...
- Tue Feb 02, 2021 10:49 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Reaction at Constant Pressure Involving Solids and Liquids
- Replies: 4
- Views: 78
Reaction at Constant Pressure Involving Solids and Liquids
In Monday's lecture, it was said that reactions at constant pressure that involve solids and liquids, the PdeltaV is insignificant, so deltaU = to enthalpy. Can someone explain why that is? Why is PdeltaV insignificant in this circumstance? Thanks!
- Thu Jan 28, 2021 1:01 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Homework number 6
- Replies: 2
- Views: 107
Re: Homework number 6
This chemical equation is an example of the enthalpy of combustion of CH4. You know this because CH4 is reacting with water to form CO2 and H2O, which are standard productions of a combustion reaction. Does that answer your question? I hope it does!
- Thu Jan 28, 2021 12:53 pm
- Forum: Student Social/Study Group
- Topic: Midterm 1
- Replies: 3
- Views: 183
Re: Midterm 1
The midterm covers up to the Friday lecture on the 22nd.
- Wed Jan 27, 2021 8:00 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: partial pressure units
- Replies: 3
- Views: 102
Re: partial pressure units
I'm pretty sure the equilibrium constant K does not have units, but for pressure the units are either barr or atm.
- Wed Jan 27, 2021 7:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Polyprotic Acids
- Replies: 1
- Views: 105
Re: Polyprotic Acids
I'm not sure but there were textbook problems about the deprotonation of acids like H2SO4 and others that have two protonations, meaning you would have to do two ice tables. I would know how to tackle these types of problems!
- Wed Jan 27, 2021 7:29 pm
- Forum: Polyprotic Acids & Bases
- Topic: Second deprotonation
- Replies: 2
- Views: 147
Re: Second deprotonation
I had the same question. When I was doing the textbook problems, I read that you ignore the second protonation when the Ka value of the second protonation is less than the first. So basically when KA2 < than KA1.
- Sun Jan 24, 2021 12:29 am
- Forum: Administrative Questions and Class Announcements
- Topic: Resources on Midterm 1
- Replies: 2
- Views: 98
Re: Resources on Midterm 1
I'm sure they will be provided, as the list is very long. My guess is that they will provide the resources on a problem-by-problem basis, meaning that for a midterm on the exam there will be a table with the information needed for that particular problem. Or we will be allowed to print out the table...
- Fri Jan 22, 2021 3:16 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Selecting a Method + Using the Tables
- Replies: 1
- Views: 38
Selecting a Method + Using the Tables
Hello! I was wondering if there is a particular way to decide which method to use for solving enthalpies. Are there key words that we should look out for? Also, will we be allowed to print out the tables with all the bond enthalpies and all that good information for the exams or will we be given the...
- Fri Jan 22, 2021 3:08 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm 2 Content
- Replies: 18
- Views: 642
Re: Midterm 2 Content
I heard from people in a UA session that today, Friday, is the last lecture that covers content in Midterm I. So there's a little bit of thermodynamics on the midterm, in addition to Acids and Bases and Chemical Equilibrium.
- Wed Jan 20, 2021 4:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Solids In Reaction
- Replies: 4
- Views: 118
Solids In Reaction
This is a long one boys! In a textbook problem 5.61 it gives the photosynthesis reaction 6 CO2 (g) + 6H2O (l) ---> C6H12O6 (aq) + 6O2 (g). For this problem, it asked what affect the addition of water would have on the overall reaction, to which I said it would have no effect because water is already...
- Wed Jan 20, 2021 4:28 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 5.39
- Replies: 1
- Views: 65
Textbook Problem 5.39
Hello! I was doing this textbook problem and had a question. When finding the Kc value for the reaction at 298K, the table says 6.1x10^23. Because the table gives the reaction for N2O4 -> 2NO2, I realized to do 1/(6.1x10^23); however the textbook goes the inverse of (6.1x10^-3) and was wondering if ...
- Sat Jan 16, 2021 3:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Week 2 Homework, Question #10
- Replies: 1
- Views: 66
Week 2 Homework, Question #10
Hello!
Last quarter we learned that if the pH < pKA then it'll be neutral predominant species and if the pH > pKA then there will be a charged predominant species. This may not make sense, but can someone explain this same concept in terms of pOH and pKB. I struggle a lot with bases :/. Thanks!
Last quarter we learned that if the pH < pKA then it'll be neutral predominant species and if the pH > pKA then there will be a charged predominant species. This may not make sense, but can someone explain this same concept in terms of pOH and pKB. I struggle a lot with bases :/. Thanks!
- Sat Jan 16, 2021 3:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Week 2 Homework, Problem#8
- Replies: 4
- Views: 104
Week 2 Homework, Problem#8
Hello! I wanted to confirm how to approach all types of these questions? When we first started doing these kinds of problems, I struggled with deciding if I should write the equilibrium starting with NH3 in water or NH4Cl in water. Is it safe to assume that we should write the equilibrium for the ac...
- Thu Jan 14, 2021 1:07 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pKA, pKB, KA, KB
- Replies: 7
- Views: 348
pKA, pKB, KA, KB
Hello!
I had a clarifying question. It's my understanding that high KA values and lower pKA values indicate a stronger acid. I was wondering if someone could explain that same concept for bases. Does a higher KB and lower pKB suggest a stronger base? Thanks!
I had a clarifying question. It's my understanding that high KA values and lower pKA values indicate a stronger acid. I was wondering if someone could explain that same concept for bases. Does a higher KB and lower pKB suggest a stronger base? Thanks!
- Wed Jan 13, 2021 7:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Net Ionic Equation
- Replies: 3
- Views: 110
Net Ionic Equation
Hello!
This was discussed in 14A, but I need a refresher. I was wondering if someone could explain how they get to that answer (bottom right corner). Thanks!
This was discussed in 14A, but I need a refresher. I was wondering if someone could explain how they get to that answer (bottom right corner). Thanks!
- Wed Jan 13, 2021 2:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Conjugate Seesaw
- Replies: 3
- Views: 146
Conjugate Seesaw
Hello! In lecture, Lavelle said that stronger acids have weak conjugate bases and stronger bases have weak conjugate acids. I was wondering if this is true for the inverse, so if there is a weak acid, is the conjugate base stronger? And if so, they are not considered strong bases like the hydroxides...
- Fri Jan 08, 2021 3:56 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: sapling week 1 #9
- Replies: 15
- Views: 677
Re: sapling week 1 #9
I would also like to add that when setting up the equation after the ICE table, to set it equal to 1/Kc, since you are now using the reverse reaction. I think this applies for number 10 as well!
- Fri Jan 08, 2021 2:20 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Endothermic vs Exothermic
- Replies: 1
- Views: 94
Endothermic vs Exothermic
This may be a non-brainer for some people, but why are endothermic reactions favored? Or did I misunderstand what was said in lecture today? Thanks!
- Wed Jan 06, 2021 10:12 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Honors Program
- Replies: 1
- Views: 126
Re: Honors Program
Hello! There are a couple of places to look for the Honors Program! I found this website with information about the application and requirements, as well as an email that you can contact with any questions. I hope this helps! http://www.honors.ucla.edu/college-honors-program/joining-the-program/ (P....
- Wed Jan 06, 2021 10:07 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Intermediate Values of K
- Replies: 6
- Views: 131
Intermediate Values of K
Hello!
This may be a very nuanced question, but I know intermediate values of K suggest that neither reactants or products are STRONGLY favored in the reaction. In these situations, are the products or reactants favored at all, even if weakly or is that not the case? Thanks!
This may be a very nuanced question, but I know intermediate values of K suggest that neither reactants or products are STRONGLY favored in the reaction. In these situations, are the products or reactants favored at all, even if weakly or is that not the case? Thanks!
- Wed Jan 06, 2021 10:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How do you know when to use Kc vs Kp?
- Replies: 9
- Views: 523
How do you know when to use Kc vs Kp?
In lecture today, Dr. Lavelle said that most problems should specific whether they want Kc or Kp; however, none of the Module problems specified whether they wanted use to solve Kc or Kp. I understand that the problem will hint at whether it's Kc or Kp when giving partial pressure or concentration, ...
- Fri Dec 11, 2020 11:32 am
- Forum: Significant Figures
- Topic: Things to remember for final?
- Replies: 20
- Views: 1207
Re: Things to remember for final?
Do we need to memorize the strong/weak acids and bases. For the most part I have em down, but I just want to make sure. Thanks Hey! I learned a way to memorize the strong acids from the UA sessions. Its as follows: "SO I BRought NO CLean CLOthes" SO refers to H2SO4, I refers to HI, BR ref...
- Thu Dec 10, 2020 2:21 pm
- Forum: Balancing Chemical Reactions
- Topic: Diatomic Molecules
- Replies: 7
- Views: 776
Re: Diatomic Molecules
Diatomic molecules are molecules composed of two atoms that are the same. Some examples are H2, O2, N2, F2, I2, Cl2, Br2.
- Wed Dec 09, 2020 1:07 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH>pKA
- Replies: 3
- Views: 196
Re: pH>pKA
Hello! I was taught this in a UA session last night. When the pH < pKa, it means the environment is acidic, so the molecule has no reason to give a proton and make the solution more acidic, so it will make the acid neutral. When the pH > the pKa, it means the environment is basic. If the environment...
- Wed Dec 09, 2020 1:00 pm
- Forum: Polyprotic Acids & Bases
- Topic: CO2 + H2O
- Replies: 7
- Views: 948
Re: CO2 + H2O
Hello! CO2 reacts with water to make carbonic acid , H2CO3. Carbonic acid is a strong acid, meaning it gives off H+ protons very readily. Carbonic acid will give off an H+ proton, making it HCO3-, which is bicarbonate, a weaker acid than carbonic acid. Once the carbonic acid has given off a proton, ...
- Wed Dec 09, 2020 11:48 am
- Forum: Bronsted Acids & Bases
- Topic: Strong vs weak acid/base
- Replies: 2
- Views: 131
Re: Strong vs weak acid/base
Hey! The best method is unfortunately memorization but the other day I found a pneumonic for remembering the strong acids. Its "SO I BRought NO CLean CLOthes" SO refers to H2SO4, I refers to HI, BR refers to HBR, NO refers to HNO3, CL refers to HCl, and CLO refers to HClO4/HClO3. I hope th...
- Mon Dec 07, 2020 4:26 pm
- Forum: Bronsted Acids & Bases
- Topic: Telling whether something is an acid or a base
- Replies: 3
- Views: 224
Telling whether something is an acid or a base
I am having an incredibly hard time identifying whether something is an acid or a base just by either 1) looking at it or 2) using methods that were talked about in class. I understand compounds with (OH) attached tend to be bases, but for example LiClO4 (Li being an ion just floating around and ClO...
- Thu Dec 03, 2020 3:55 pm
- Forum: Naming
- Topic: Naming Order
- Replies: 16
- Views: 616
Naming Order
Hello! I understand that when writing the name, the ligands are in alphabetical order, but how about when writing the formula? For example (just making this up), [Co(OH)3(NH3)4]. In this case, ammine would go first, but what if we were given the name first and had to work backgrounds to write the fo...
Re: Naming
Usually the name would be smashed all together and usually the textbook and other people separate it with hyphens to make it more clear. I don't think either one is incorrect, but I would be comfortable with reading both. The long, smashed ones tend to be harder to read, but I would just be okay wit...
- Wed Dec 02, 2020 12:30 pm
- Forum: Naming
- Topic: Sapling wk 9 question 1
- Replies: 4
- Views: 225
Re: Sapling wk 9 question 1
I have yet to start the homework, but just by looking at your answer I worked backwards to get the formula. [Co(NH3)5Cl]Cl. The Cl inside and outside both have a -1 charge, and ammine has no charge. Adding the two -1 charges from the chlorine ions would make a -2 total charge, but since everything ...
- Wed Dec 02, 2020 12:29 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: oxidation number with outside bracket charge
- Replies: 4
- Views: 249
Re: oxidation number with outside bracket charge
Hello!
The -2 on the outside means that the molecule has an overall charge of -2. Because you have 6 Chlorines, each with a -1 charge, that makes -6. Because the molecule has a -2 overall charge, you now know that Pt has an oxidation number of +4. I hope this makes sense!
The -2 on the outside means that the molecule has an overall charge of -2. Because you have 6 Chlorines, each with a -1 charge, that makes -6. Because the molecule has a -2 overall charge, you now know that Pt has an oxidation number of +4. I hope this makes sense!
- Wed Dec 02, 2020 12:07 pm
- Forum: Naming
- Topic: Sapling wk 9 question 1
- Replies: 4
- Views: 225
Re: Sapling wk 9 question 1
I have yet to start the homework, but just by looking at your answer I worked backwards to get the formula. [Co(NH3)5Cl]Cl. The Cl inside and outside both have a -1 charge, and ammine has no charge. Adding the two -1 charges from the chlorine ions would make a -2 total charge, but since everything i...
- Mon Nov 30, 2020 5:22 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Polydentate vs Monodentate
- Replies: 10
- Views: 642
Re: Polydentate vs Monodentate
Hello! We went over this today in Lavelle's office hours and he recommended drawing out the structures to see which have atoms with single bonds and lone pairs that could bond. If the ligand has more than one atom that has a single bond and a lone pair available to bond, then that ligand is polydent...
- Mon Nov 30, 2020 4:31 pm
- Forum: Biological Examples
- Topic: Effects of Partial Pressure
- Replies: 1
- Views: 118
Re: Effects of Partial Pressure
Hello! I am a little rusty on the 7 series information, but I'm sure others can add to this. Essentially, we know that gases like to naturally move from higher partial pressure to lower partial pressure. In the pulmonary capillaries, the partial pressure of oxygen is very high, causing oxygen to bin...
- Wed Nov 25, 2020 3:58 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: H2O VSEPR
- Replies: 27
- Views: 1211
Re: H2O VSEPR
H2O would actually be bent shape because the two electron pairs from the oxygen will push the bonds between hydrogens down, giving it a bent shape.
- Wed Nov 25, 2020 3:22 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polar and Nonpolar Bonds vs Molecules
- Replies: 2
- Views: 220
Re: Polar and Nonpolar Bonds vs Molecules
So polar/nonpolar bonds refer to the specific bonds within a molecule. Polar and nonpolar molecules refer to the overall molecule. So for example, H2O has polar bonds and is overall a polar molecule. On the other hand, CO2 also has polar bonds, but because the structure is linear and the dipoles can...
- Wed Nov 25, 2020 11:53 am
- Forum: Hybridization
- Topic: Unhybridized Orbitals
- Replies: 2
- Views: 174
Unhybridized Orbitals
Hello! I was having trouble how to find out if an orbital is unhybridized. In his Monday lecture, Professor Lavelle would point a some part of the molecule, explaining that it did not have a hybrid orbital, and I wanted to know how you can tell that when looking at a molecule? Thank you and happy ho...
- Tue Nov 24, 2020 9:09 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Sapling Question #18
- Replies: 2
- Views: 136
Sapling Question #18
Hello! I had a question on Sapling HW #8. The question was: "Select the correct statement about the relative positions of the hydrogen atoms in the three structures. a. The hydrogen atoms of H2CCCH2 and H2CCCCH2 lie in the same plane. b. The hydrogen atoms of H2CCH2 and H2CCCCH2 lie in the same...
- Tue Nov 24, 2020 5:45 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem 14B
- Replies: 9
- Views: 435
Re: Chem 14B
I think he means to not schedule a class at the same time as the Chem 14B lecture, because although it is recorded, he plans to have exams like midterms held during lecture time rather than discussion times. I heard some students were asking if they could double-schedule Chem 14B with another class ...
- Tue Nov 24, 2020 5:18 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Number of Questions on the Final
- Replies: 1
- Views: 75
Re: Number of Questions on the Final
I'm not entirely sure, but I do know that the final is 1 hour and 30 minutes instead of a typical 3 hour final. If the midterm of 50 minutes was 12-16 questions, I would assume that it would be in the mid-20 to low 20s for the amount of questions. Hopefully he'll drop info on the final soon!
- Tue Nov 24, 2020 2:08 pm
- Forum: General Science Questions
- Topic: Sapling #8
- Replies: 4
- Views: 292
Re: Sapling #8
Hello! BeCl2 has polar bonds but is non polar overall. Because Be does not have any lone pair electrons the shape will be linear, so the dipoles from the Cl will cancel out. H2O also has polar bonds because the oxygen will pull the electrons from the hydrogen. The shape of H2O is bent though because...
- Tue Nov 17, 2020 10:08 pm
- Forum: Resonance Structures
- Topic: Sapling #5
- Replies: 2
- Views: 134
Re: Sapling #5
First, you would want a negative charge on the most electronegative element in the molecule. Second, because carbon is the central atom, you do not want a charge on it (or any central atom for that matter) because it makes the molecule very unstable, making it unfavorable. Hope this helps!
- Tue Nov 17, 2020 5:53 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: Intermolecular Forces of CHI3 and CHF3
- Replies: 5
- Views: 1202
Re: Intermolecular Forces of CHI3 and CHF3
For this example you would have to think about the size of the electronegative atoms. Fluorine, although very electronegative, is relatively small compared to Iodine. Because iodine is much larger, it has more electrons and making it more polarizable. Because it is more polarizable and has more elec...
- Tue Nov 17, 2020 5:37 pm
- Forum: Ionic & Covalent Bonds
- Topic: matthew tran wkshop answer key
- Replies: 1
- Views: 278
Re: matthew tran wkshop answer key
Hello! Matthew doesn't post his answer key anywhere, he only gives out answers in the UA sessions. I'm not sure if you email him, he'll send you an answer key (as many UAs deal with past exam questions, they don't want those circulating). Regardless I found his email for you: mtran060@g.ucla.edu. I...
- Tue Nov 17, 2020 8:06 am
- Forum: Lewis Structures
- Topic: Lewis Acids and Bases
- Replies: 5
- Views: 155
Re: Lewis Acids and Bases
Jaclyn Dang 3A wrote:Are lewis acids and bases going to be on this exam?
I saw it on the Outline 3 as a guideline. "Identify Lewis acids and bases", so I suppose so.
- Mon Nov 16, 2020 10:12 pm
- Forum: Lewis Structures
- Topic: Lewis Acids and Bases
- Replies: 5
- Views: 155
Lewis Acids and Bases
Hello! Can someone help me by writing a general rulebook / guidelines for identifying Lewis acids and bases? I'm struggling with identifying them on the homework and UA sessions. Thank you in advance !
- Mon Nov 16, 2020 10:10 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic and Covalent Character
- Replies: 2
- Views: 130
Ionic and Covalent Character
In a UA Session, we learned that "covalent character increases going down a group". This makes sense because as you go down a group, atomic radius increases and electrons are further out, allowing them to be easily distorted. However, does this apply to Groups 1 and 2? I'm confused because...
- Mon Nov 16, 2020 4:22 pm
- Forum: Administrative Questions and Class Announcements
- Topic: MT 2 Material
- Replies: 4
- Views: 161
Re: MT 2 Material
Correct! The last lecture that covers Midterm II material was the one from last Wednesday.
- Mon Nov 16, 2020 4:19 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Textbook 1E.17 part b
- Replies: 3
- Views: 92
Re: Textbook 1E.17 part b
When writing the electron configuration for Mn, [Ar]3d^5 4s^2. Although 4s subshell is filled first, when writing the electron configuration, the 4s subshell comes after because it has higher energy. This means that the electron will come off the last subshell in the electron configuration, which wo...
- Thu Nov 12, 2020 7:57 pm
- Forum: Lewis Structures
- Topic: formal charges
- Replies: 2
- Views: 169
Re: formal charges
Hello! You are correct in saying that the overall formal charge is -2 as indicated by the molecular formula. When doing the Lewis structure you would want to avoid putting any charge on carbon since it is the central atom. You can do this by doing a double bond with one of the oxygens. This would be...
- Thu Nov 12, 2020 2:31 pm
- Forum: Lewis Structures
- Topic: Oxygen and Hydrogen
- Replies: 1
- Views: 87
Oxygen and Hydrogen
Hello! I was hoping someone could explain, when drawing a Lewis structure, how you know whether an OH/HO is going to be an O attached to the central atom and a hydrogen extending from the oxygen versus when the hydrogen and oxygen are both connected to the central atom. I've heard that OH means an o...
- Wed Nov 11, 2020 12:29 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 1E.25
- Replies: 1
- Views: 74
Re: 1E.25
Hello! The longer and probably the safest way is to write out the electron configuration for all the elements in the group it's asking for. This will probably take time, but it's good practice. When asking for the electron configuration, it's asking for the outermost electrons (including the electro...
- Tue Nov 10, 2020 4:51 pm
- Forum: Electronegativity
- Topic: Sapling #15
- Replies: 11
- Views: 527
Re: Sapling #15
Hello! I have been to Lavelle's office hours and many UA workshops. All of them have said that Hydrogen boding is possible when the hydrogen is bonded to Nitrogen, Oxygen, or Fluorine. I'm not entirely sure as to why, and hopefully someone can provide that insight, but the general rule of thumb is w...
- Tue Nov 10, 2020 4:24 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic v. Covalent Bonding
- Replies: 16
- Views: 765
Re: Ionic v. Covalent Bonding
I think something else to note is electronegativity. We know the trends for electronegativity looking at the periodic table. Ionic bonds happen between elements that have a very large electronegativity difference (so for example, opposite sides of the periodic table), but covalent bonds happen betwe...
- Mon Nov 09, 2020 4:26 pm
- Forum: Ionic & Covalent Bonds
- Topic: "Favorable"
- Replies: 4
- Views: 195
Re: "Favorable"
For a bond to be favorable, it means the bond has a very high negative energy (example, today in class with -250 kJ/mol). A very high negative energy means that the bond is releasing a lot of energy, rather than requiring a lot of energy, making it favorable.
- Mon Nov 09, 2020 3:57 pm
- Forum: Ionic & Covalent Bonds
- Topic: Hydrogen Bonds [ENDORSED]
- Replies: 9
- Views: 502
Re: Hydrogen Bonds [ENDORSED]
Chem_Admin wrote:Lily, I will go through this in my 3pm discussion section today.
I've included an imagine to clear it up!
- Mon Nov 09, 2020 3:44 pm
- Forum: Ionic & Covalent Bonds
- Topic: Hydrogen Bonds [ENDORSED]
- Replies: 9
- Views: 502
Re: Hydrogen Bonds [ENDORSED]
Can someone please explain what a dipole dipole bond is? We learned dipole moments however I have not heard dipole in any other context until this post. Hello! I am currently in Lavelle's office hours right now. He explained dipole dipole bonds in this manner. Suppose you have two water molecules. ...
- Wed Nov 04, 2020 11:09 am
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge and Stability
- Replies: 7
- Views: 174
Re: Formal Charge and Stability
Generally, Lewis Structures with a formal charge of 0 are more stable than others with a positive or negative charge. Hope this helps!
- Wed Nov 04, 2020 11:05 am
- Forum: Ionic & Covalent Bonds
- Topic: SO4 covalent bond
- Replies: 6
- Views: 173
Re: SO4 covalent bond
To add to the previous posts, Dr. Lavelle also mentioned a few elements have the ability to have an expanded octet, such as Sulfur, allowing it to have more electrons than the 8 that are inn the octet guideline, so keep an eye out for those when they are mentioned!
- Tue Nov 03, 2020 9:45 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Second Midterm Date
- Replies: 9
- Views: 379
Re: Second Midterm Date
Week 7 during discussion!
- Tue Nov 03, 2020 9:36 pm
- Forum: Lewis Structures
- Topic: How to find valence electrons of an element
- Replies: 6
- Views: 639
Re: How to find valence electrons of an element
I found this table that helps visualize it a little bit more clearly. I hope this helps!
- Tue Nov 03, 2020 4:29 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Textbook Topic 1E #17
- Replies: 1
- Views: 73
Re: Textbook Topic 1E #17
Hello! So, Dr. Lavelle touched it briefly, but he explained that for multi-electron atoms AFTER atomic number 20, the 4s state is higher in energy than 3d, meaning the electrons would first fill up the 3d orbital, and then the 4s. So the electron configuration for Mn would be [Ar]3d5 4s2. Because th...
- Thu Oct 29, 2020 2:52 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Participation Points [ENDORSED]
- Replies: 62
- Views: 3338
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? Hi! I think it's not directly on your name by right next to your name, on the left there is like a little paper followed by "by (insert name)". I think that means "Pos...
- Tue Oct 27, 2020 9:16 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Sapling Homework #8 - Which number do we assign to n(1) versus n(2)
- Replies: 4
- Views: 210
Re: Sapling Homework #8 - Which number do we assign to n(1) versus n(2)
From my understanding, the n1 and n2 are relatively arbitrary, meaning that yes you change them depending on whether you need a positive or negative answer, so absorption vs emission. I typically use the E= -hR/(n)^2 concept and just do final energy - initial energy. This may also be a way for you t...
- Tue Oct 27, 2020 5:32 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Participation Points [ENDORSED]
- Replies: 62
- Views: 3338
Re: Participation Points [ENDORSED]
Awesome! Thanks :D
- Tue Oct 27, 2020 12:25 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Participation Points [ENDORSED]
- Replies: 62
- Views: 3338
Participation Points [ENDORSED]
Is there any way to check to see if you're getting your participation points through Chemistry Community? I tend to post 5-7 times a week, but I'm not sure if all my posts are "valid" posts to get points and was wondering if there was any way to find out? Thanks!