CHEMISTRY COMMUNITY

Alara Aygen 3K

You'll need 200 points out of 400 points to pass.

Alara Aygen 3K

I also agree with what every has said; I find finals usually more challenging.

Alara Aygen 3K

All time favorites: Sherlock Holmes, Big Bang Theory, Friends, and Queen's Gambit. Recently I started watching Blacklist and I would highly recommend it!

Alara Aygen 3K

To find the moles you need to divide mmol by 1000.

Alara Aygen 3K

I think the number of problems for a certain topic is proportional to the time we spent on it.

Alara Aygen 3K

Kinetics is about the speed/rate of a reaction. Thermodynamics is used to figure out the general properties of reactions and includes concepts such as enthalpy and entropy.

Alara Aygen 3K

I was struggling with the concept too, thank you for these detailed answers!

Alara Aygen 3K

Best oxidizing agents have the best reduction potential.

Alara Aygen 3K

Thank you for creating this thread, sounds very interesting!
Here is my chemistry fun fact: Superfluid Helium can climb walls! If you're interested, I am adding a link to the Scientific American article about this topic: https://www.scientificamerican.com/arti ... imb-walls/

Alara Aygen 3K

Thank you all for the tips; these are really helpful!

Alara Aygen 3K

I was having trouble with this too, thanks!

Alara Aygen 3K

Congratulations to everyone! We're almost there!

Alara Aygen 3K

Taking walks and watching my favorite shows really help me to ease my mind!

Alara Aygen 3K

I feel the same way! Reading these helped me, so thank you!

Alara Aygen 3K

Last quarter Dr. Lavelle created many extra final review sessions. They really helped me. If he does it again this quarter, I highly suggest attending them.

Alara Aygen 3K

Hello! I would use lewis structures to find formal charges and chemical formulas to find oxidation numbers—formal charge divides bonding pairs equally, and oxidation numbers assign both the electrons in a bonding pair to the more electronegative atom in the pair. However, both should add up to the ...

Alara Aygen 3K

I believe that is the equation for internal energy of an ideal gas.

Alara Aygen 3K

Hello, I am also very nervous but here are some things I'm doing to help myself feel more prepared for the test! 1.) Of course, workin on sapling and tb problems, but also making note of what TYPES of questions there are (how they ask the question). Often times the question itself seems very daunti...

Alara Aygen 3K

I love apple pie and ice cream!

Alara Aygen 3K

I think Dr. Lavelle teaches general chemistry and since 14C is organic chemistry we'll have a new instructor.

Alara Aygen 3K

dT uses integrals to find really small changes in temperature. Delta t is much bigger since it is the overall change in temperature.

Alara Aygen 3K

I usually write down the "known" and "unknown" values and figure out which equation is better to use with the given information.

Alara Aygen 3K

I am currently taking 14BL and I would have preferred taking it inperson. If you have the chance and time to take it inperson, it might be more beneficial since you will be able to study in an actual lab.

Alara Aygen 3K

I think Hess's Law and standard enthalpies have relatively the same level of accuracy, and they are both more accurate than the bond enthalpies.

Alara Aygen 3K

Wow! These are all very interesting posts. I will definitely check out some of these videos.

Alara Aygen 3K

Was there a way to make up missed points last quarter?

Alara Aygen 3K

I believe it will be similar to last quarter, so maybe they will be out by this Friday.

Alara Aygen 3K

I think the grading scale gets finalized after the final. For now we know that a C- equals to 50%

Alara Aygen 3K

In endothermic reactions heat goes into the system and results in a positive delta H. In exothermic reactions heat goes out of the system and results in a negative delta H.

Alara Aygen 3K

I also felt like it was harder than I have expected.

Alara Aygen 3K

That was the change in temperature. (Final temperature = 31.9 degrees Celsius) - (Initial temperature = 25 degrees Celsius) = 6.9
Then you plug that value in the equation: (mass)x(specific heat capacity)x(delta T = change in temp) to find the value of heat given off by the reaction.

Alara Aygen 3K

Yes, you need to convert to moles as it is the correct unit for that calculation (unless it specifically asks for mmol).

Alara Aygen 3K

Hi, can someone explain me when we leave out -x (in the denominator) while calculating the equilibrium constant/concentrations?

Alara Aygen 3K

Reviewing sapling questions and doing the problems in the outline really help.

Alara Aygen 3K

I sometimes have the same problem. Putting the numbers that have powers in parentheses solves the problem.

Alara Aygen 3K

I don't think pka equals to pH. pKa is the negative log of the acidity constant, Ka, but I believe they can be used to find out the pH of the solution since pH depends on [H3O+] concentration as well.

Alara Aygen 3K

Doing the problems mentioned in the outlines and attending the UA workshops really help!

Alara Aygen 3K

pKa is the -log of Ka. This means higher the Ka, smaller the pKa and vice versa

Alara Aygen 3K

You can determine it by the information you are given in the problem. For example if it says there was an addition to one of the reactants you can put a +x in the second row of that reactant. That would mean the product is decreasing as the reaction is favoring the reactant.

Alara Aygen 3K

It is because weak acids and bases do not completely disassociate in water. If it was a strong acid or base you could directly used the concentration because you would know that the concentration of the acid or base would equal to the concertation of [H30+] or [OH-] as they completely disassociate i...

Alara Aygen 3K

When you write out your Kc expression, you get Kc= (2x)^2/ (xx- x)^2. Algebraically, you can take the square root of both sides, to cancel out the squares on the rigth side of the equation in order to make it easier for yourself to calculate. That's why you'd have 2x/(xx-x), instead of (2x)^2/ (xx-...

Alara Aygen 3K

I am having trouble understanding that problem as well. How did you know we need to use 2X instead of (2X)^2?

Alara Aygen 3K

Yes! A high K value indicates that the reaction favors the products, which means it is more soluble.

Alara Aygen 3K

We look at the stoichiometric coefficients. If we assume O2 has changed by -X, we can safely assume that N2 and N2O have changed by -2X and +2X respectively because both of their stoichiometric coefficients equal to two.

Alara Aygen 3K

Alara Aygen 3K wrote:I believe it is found through experimentation

But can someone explain why [H3O+] and [OH-] concentrations need to be equal?

Alara Aygen 3K

Kw is the equilibrium constant for: [H3O+][OH-] (the autoprotolysis of water)

Alara Aygen 3K

I believe it is found through experimentation

Alara Aygen 3K

Q represents a constant at a specific time during the experiment. That's why if Q is bigger than or smaller than K, the reaction will shift because it won't be at equilibrium. If Q=K, then, it is at equilibrium. Hope this helps.

Alara Aygen 3K

Hi, Dr. Lavelle sent out an email earlier today with TA Office Hours and Discussion sections for lecture 1 and 2. He said there was a problem with the zoom links for lecture 3, and those links will be posted once the problem is fixed. I'm not sure when they'll be posted on CCLE.
Hope this helps.

Alara Aygen 3K

I think changing temperature changes the rate at which the equation takes place. So, in this case the rate would be slower at lower temperatures.

Alara Aygen 3K

Hello, I just wanted to clarify something. When we want to determine the favored substance (products or reactants) do we look at the denominator and numerator of the Kc equation [if the denominator is bigger reactants are favored and if the numerator is bigger products are favored]? Also what does &...

Alara Aygen 3K

They are used interchangeably.

Alara Aygen 3K

If you are given a base and asked to find the conjugate acid, you need to add one H atom since Bronsted bases are proton acceptors.
If you are given an acid and asked to find the conjugate base, you need to remove one H atom, since the Bronsted acids are proton donors.

Alara Aygen 3K

Ligands attach to the central metal ion and form coordination compounds.

Alara Aygen 3K

Hi! Does anyone know what are the topics of the step-up sessions during this week? In the "final review sessions" pdf, every review session has a topic except for the step-up sessions. Are they general review?

Alara Aygen 3K

Hi! They are inversely related. KA is the concentration of the acid, so higher the KA stronger the acid. pKA correspond to the pH scale, so higher the pKA weaker the acid.

Alara Aygen 3K

Hi! Electron geometry is the arrangement of electron groups. Molecular geometry is the arrangement of atoms.

Alara Aygen 3K

Electron density around the nuclei is higher in sigma bonds than in pi bonds. This causes sigma bonds to be stronger.

Alara Aygen 3K

Hi! Resonance structures represent the same compound. The only aspect that differs is the arrangement of electrons (the number of electrons are the same).

Alara Aygen 3K

Hi! I was wondering how everyone will be studying for the final. Since it will be cumulative I don't know where to start studying. Does anyone have any tips?

Thank you in advance!

Alara Aygen 3K

Finals are after week 10. So you don't have to worry about lectures. Downloading your calendar from MyUCLA might help you to track them better.

Alara Aygen 3K

Thank you!

Alara Aygen 3K

Hi! A delocalized pi bond means that electrons are free to move over the nuclei.

Alara Aygen 3K

Does anyone know when we can expect our results, before or after the holiday?

Alara Aygen 3K

I feel the same way. I was hoping for a really good exam; I thought I understood the topics well, but it was worse than the first one.

Alara Aygen 3K

I try to go on regular walks where I can rest my mind and focus on nature.

Alara Aygen 3K

I used to be like that too, taking wordy and lengthy notes. After the first midterm, I focused more on solving questions than taking long notes.

Alara Aygen 3K

I believe that the most stable structure will be among one of the resonance structures you draw. The structure which the formal charges of the individual atoms are closest to zero will be favored. Also, you can look at the most electronegative atom, if it has the negative formal charge that structur...

Alara Aygen 3K

The ion-ion forces between NaCl is stronger than the dipole-dipole interactions between HCl molecules. As the bond gets stronger, the boiling/melting point increases since more energy will be needed to break the bonds.

Alara Aygen 3K

I will personally take them together, but there are also people who want to take BL after they take 14B.

Alara Aygen 3K

Hello! Can someone tell me how many orbitals can n=7 have?

Alara Aygen 3K

Hi! Can someone explain me why two NO molecules cannot form hydrogen bonds?

Alara Aygen 3K

Electronegativity is the ability to attract electrons. Electron affinity is the amount of energy released when a new electron is added to the neutral atom. Ionization energy is the minimum energy needed to remove the least tightly held electron. Hope this helps!

Alara Aygen 3K

H bonds usually happen between H atoms and more electronegative atoms like F, O, and N. They are more like attractions than actual bonds. So, I don't think it is a coordinate covalent bond.

Alara Aygen 3K

I would call out green just to be sure.

Alara Aygen 3K

Electronegativity is the ability to attract electrons. Electron affinity is the amount of energy released when a new electron is added to the neutral atom.

Alara Aygen 3K

If the atom pulls the electrons it is delta negative and if the electrons are moving away from an atom it is delta positive

Alara Aygen 3K

I believe they are different

Alara Aygen 3K

Hi! In today's lecture Dr. Lavelle mentioned two different SO4^-2 structures. One of them had a double bond. Can someone explain me why it is a better representation and how do we choose which structure to use?

Alara Aygen 3K

You also need to think about the overall charge of the molecule. In NO3^- , it is minus 1. For example, in SO4^-2 it is -2. If the overall charge is negative you add that number of electrons to the other electrons to find the total electrons. If the overall charge is + (e.g. NH4^1) you substract tha...

Alara Aygen 3K

Hi! Can someone explain me the reason why delocalized electrons have additional stability?

Thanks in advance!

Alara Aygen 3K

I tried to take Chem 14A last spring, but it was already full by the time of my second pass. So, I would suggest you take it during your first pass because this class fills up fast too. However, if you think you have other classes that may fill up faster then go with them!

Alara Aygen 3K

Hi! It should be the atomic number.

Alara Aygen 3K

I would write more chemistry jokes, but all the good ones argon.

Alara Aygen 3K

The theoretical yield is the maximum amount of product you can get based on your calculations. However, this amount is usually not achieved in the actual experiment because of technicalities. Thus, the theoretical yield is usually higher than the actual yield.

Alara Aygen 3K

Hi! If it is Lyman series, n=1 should be in the equation. However, don't assume it only has to be the final state. If the e- is absorbing energy than n=1 is probably the initial state. Similarly, if e- is emitting energy than n=1 is probably the final state. Hope this helps!

Alara Aygen 3K

Hi! If it is Lyman series, n=1 should be in the equation. However, don't assume it only has to be the final state. If the e- is absorbing energy than n=1 is probably the initial state. Similarly, if e- is emitting energy than n=1 is probably the final state. Hope this helps!

Alara Aygen 3K

Yes, you should convert the units to m and kg if you are using De Broglie's equation for other units to cancel out.

Alara Aygen 3K

Hello,

I did the sapling homework (except for 3 questions, which I'll do by the end of this week) and currently my score is 90% on sapling. However, the grade section on CCLE did not update itself. Do you know when it updates the score or what should I do if it doesn't update?
Thanks in advance!

Alara Aygen 3K

Hi,

It is negative because the electron is going from a higher energy level to a lower energy level, thus losing energy. Also keep in mind that the electron has started with 0 energy.

Alara Aygen 3K

I believe they are the same thing

Alara Aygen 3K

I might be wrong about this but I believe it can detect molecules because every molecule absorb different wavelengths.

Alara Aygen 3K

I believe it is energy per electron. You might need to convert it to moles if the question specifically asks you to do so.

Alara Aygen 3K

It should be kg! It will cancel out with Planck's constant.

Alara Aygen 3K

Hi, This is a question from the homework. It is asking for the maximum number of electron that can be ejected by a burst of photons with a total energy of 9.69x10^-7 J. I calculated the work function as 5.54x10^-19 J/photon. I thought that "work function x # of e-" should equal to the tota...

Alara Aygen 3K

Yes, the first time they conducted the experiment they called it the threshold energy because the amount of energy needed to eject an electron had to be higher than that. I believe the work function is a more accurate term, but they mean the same thing.

Alara Aygen 3K

Hi, Additionally to what everyone has said, this is from his last email: "Posting admin questions in a Quantum section, or Fundamentals questions in a Quantum section, is clearly not valid and makes a mess of the forum that is carefully organized by topic to assist students. To receive Chemistr...

Alara Aygen 3K

Hello, can someone explain me how to solve this question please? "Molybdenum metal must absorb radiation with a minimum frequency of 1.09x10^15 /s before it can emit an electron from its surface. If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the e...

Alara Aygen 3K

Hello, this was a question from the audio-visual focus assessment modules and I can't find the correct answer. "Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 10^5 m/s. The work function for sodium is 150.6 k.J /mol. What is the kinetic energy of the ejecte...

Alara Aygen 3K

Hello, this was a question from the audio-visual focus assessment modules: "To interpret the result of photoelectric experiments the model of light needs to change from a _________ model to a _________ model." I said "wave, photon" but apparently it is wrong. Can someone tell me ...

Search found 107 matches