CHEMISTRY COMMUNITY

Ryan Hoang 1D

For this q, How do you know that MnO4- reduces to Mn2- and Fe2+ oxidizes to Fe3+?
Is this just because that’s what it says in the back of the textbook appendix? Or is there some better way to know what it changes to?

Ryan Hoang 1D

Since K + (aq) is not part of the redox reaction, don't need to include it. If you do include it shows on the left and right side of the chemical equation and cancels out as it is the same species at the same concentration on both sides of the chemical equation. We saw this in class when calculatin...

Ryan Hoang 1D

Please include the entire problem in future posts. When you write the half reactions, you will see that the half reaction that involves Cd(OH)2 requires OH- to be present. KOH is simply a supply of OH- telling you that OH- is involved. You can also just write OH- or any other source of OH like NaOH...

Ryan Hoang 1D

Hello! So for they ask us to balance and write the cell diagram for this reaction Ce4+(aq) + I-(aq) -> I2(s) + Ce3+(aq). I managed to balance it out with me getting 2Ce4+(aq) +2 I-(aq) -> I2(s) + 2Ce3+(aq) which was correct. However, when i tried to draw the cell diagram, I put I2(s)|I-(aq)||(Ce4+,...

Ryan Hoang 1D

Hello! So for they ask us to balance and write the cell diagram for this reaction Ce4+(aq) + I-(aq) -> I2(s) + Ce3+(aq). I managed to balance it out with me getting 2Ce4+(aq) +2 I-(aq) -> I2(s) + 2Ce3+(aq) which was correct. However, when i tried to draw the cell diagram, I put I2(s)|I-(aq)||(Ce4+,C...

Ryan Hoang 1D

I actually had the same question, so I'm going to add myself in this post so I can go back in case an answer gets posted.

Ryan Hoang 1D

I miss friends, and just being able to generally talk to people. It's been so hard without social interactions man, and I just miss being able to smile and say hi to people. :)

Ryan Hoang 1D

Yeah! So you do the same exact thing that you do for acidic solutions, adding H+ and H2O as needed. However, at the end, you add OH- to the H+ (and if you do something one one side, you have to do it to the other side). This will then get you the equation that you need!

Ryan Hoang 1D

The intermediates will be given to you-> but generally, the elementary rate determining step will be the one that is expressed in the overall rate law!

Ryan Hoang 1D

Burnouts been so hard for me. I think just taking breaks and going for walks/drives around really helps me, and is something I'd recommend. Being able to get your head out of studying all the time helps (but make sure your breaks don't turn into 2 hour youtube binges like me!)

Ryan Hoang 1D

Yeah! So, one of the first things you'd have to do is understand if the type of order that it's in. From there, you can determine which equations to use as necessary. If it tells you, then apply the equations for each order using whatever you're given!

Ryan Hoang 1D

Hi! Yeah, so Dr. Lavelle actually derived this in lecture #23 at the beginning if you'd like to go rewatch it. But otherwise, I'll just quickly explain. So the value of 0.693 for half rates comes from 1st order reactions, and is found by setting t=t at 1/2. We know then, that [A]=1/2[A]. From there,...

Ryan Hoang 1D

If you're talking about the rate law or the integral rate laws, we need to use both calculus to derive the equation, as well as experimental data to find the values for the rate law for a chemical reaction. So, as Dr. Lavelle went over in his lectures, he explained how to find the integral rate laws...

Ryan Hoang 1D

Basically, that's when there's been no voltage transfer, and it's almost like the battery is brand new. This is since, as voltage gets transferred over, some of the anions have to move, and some of the metal on the anode side gets transferred into solution, while the cathode on the right side gets p...

Ryan Hoang 1D

Nick Saeedi 1I wrote:If you are referring to KClO3, the ion is ClO3- not Cl. Thats why u can't refer to Cl- as the monoatomic.

Ohh, that makes so much more sense. Wow, did not realize it was a polyatomic, thank you so much!

Ryan Hoang 1D

Yeah! So, with this one, you'd want to use the Nernst equation E=Edot-0.05916V/nlogQ to solve. But, to get Edot, you'd use Ecell=Ecathode-Eanode, to find Ecell of the overall reaction. From there you can apply Nernst equation to solve for E or the cell potential. This may be a dumb question. But ho...

Ryan Hoang 1D

For the reaction KClO3⟶KCl+3/2O2 assign oxidation numbers to each element on each side of the equation. I know that monoatomic ions have an oxidation state that fits its charge. However, why does K then have an oxidation number automatically equal to 1, but not Cl? How do we know that K is the monoa...

Ryan Hoang 1D

Yeah! So, with this one, you'd want to use the Nernst equation E=Edot-0.05916V/nlogQ to solve. But, to get Edot, you'd use Ecell=Ecathode-Eanode, to find Ecell of the overall reaction. From there you can apply Nernst equation to solve for E or the cell potential.

Ryan Hoang 1D

What I find easier is to treat it like an acidic solution and then covert. It is easier to balance H and O. Once you find the half reactions, balance everything except for H and O. Then add water to balance the O. Then add H+ to balance H, and this should also balance the charges. Make sure the mol...

Ryan Hoang 1D

A system is thermodynamically unstable if their Change in Gibbs Free energy is negative. This is because, when the values are negative, it'll spontaneously react to form a new, more stable compound.

Ryan Hoang 1D

All the other posters are right, but I just wanted to expand a little on why lower energy states is more stable! A good analogy to think about a hill. At the top of the hill, your energy potential (due to gravity) is high, but because of this, you're unstable. If you get pushed down that hill, you'l...

Ryan Hoang 1D

Hm... I've talked to some other biochem majors and they've told me previously that as a biochem major, you're supposed to take the 20A/b series for chemistry, not the 14a/b series. 14a/b is for all life science majors EXCEPT for biochemistry... with that being said, I'm still not a professional/expe...

Ryan Hoang 1D

Yeah, so think of OIL RIG when you first do oxidation and reduction. OIL RIG stands for: oxygen is loss, and reduction is gain (in electrons). So just try seeing how the electrons interact within the context of the equation to produce this oxidation/reduction.

Ryan Hoang 1D

I love mnemonics, so thank you for this very helpful mnemonic!

Ryan Hoang 1D

Hey Stella, When approaching problems with a lot of numerical info like these, it helps to translate everything in the problem into a set of mathematical expressions: ΔS o vap @100 o C = 109J/Kmol C P liquid = 75.3J/Kmol C P vapor = 33.6J/Lmol ΔS o vap @85 o C = ? Based on those given values it's g...

Ryan Hoang 1D

Hello! So I understand what standard entropy of vaporization is, especially for example, at boiling point of water at 100 degrees C. To my understanding, it's the amount of states/disorder that are achieved as the liquid goes from liquid to gaseous. HOWEVER I don't understand how standard entropy of...

Ryan Hoang 1D

Yeah, often times internal energy is represented as an E, not as a Q. But also, careful you’re looking at internal energy equation, not Gibb’s free energy or the other multitude of equations

Ryan Hoang 1D

I don’t think so... Because the amount of states that oxygen can be in are the same, with degeneracy of 1. Then, we’d take Boltzmann eq, and solve which would end up getting the same number of entropy. Again, someone correct me if I’m wrong here

Ryan Hoang 1D

I believe so, since the Se is the central atom, and all the other Os must revolve around it, theres no room for positional entropy. However, if I’m wrong, it’d be nice for someone to correct me!

Ryan Hoang 1D

I believe so, since the Se is the central atom, and all the other Os must revolve around it, theres no room for positional entropy. However, if I’m wrong, it’d be nice for someone to correct me!

Ryan Hoang 1D

I just feel like it can be hard to disconnect the two, when you work super hard and end up still doing bad and worse than a large portion of the class. Oh well, I suppose.

Ryan Hoang 1D

The other poster is correct. Just keep in mind, C alone is normally just the specific heat.

Ryan Hoang 1D

I 100% agree with Lauren, looking at the units helps a lot! But, I also remember to use the 8.31 value when dealing with work, but when trying to find out moles/volume/etc in order to get to actually solve that work problem, I'd normally use 0.08206. However, Lauren's tip of looking at units is prob...

Ryan Hoang 1D

Yep! Then, you'd use ΔU=q+w to figure it out from there. Just remember: when a system is RELEASING heat, that means q is negative. When work is done ON a system, that work is positive (as it absorbs energy)

Ryan Hoang 1D

Cv is the specific heat at a constant volume, and Cp is the specific heat at a constant pressure. Since solids and liquids can't change volumes, we know for all that Cp = Cv. Just to add on: liquids and solids can't change volumes because they're not compressible anymore. They already are very comp...

Ryan Hoang 1D

Dr. Lavelle really loves his step-up and worksheets and other office hours that you could go to!

Ryan Hoang 1D

Yeah, I like to think of it as "chaos!" The more entropy, the more chaos (so the more states that a gas molecule can take up). The world trends towards chaos or disorder (and more states being open for the atoms/molecules to take up position in).

Ryan Hoang 1D

Yeah! So basically, you can use the w=-RT lnV2/V1 as the work for irreversible isothermal process. Delta U=3/2 n R delta T=0 is just the isothermal reversible expansion in 3D, and q=-w is that work done by a system in isothermal reversible expansion is replaced by heat.

Ryan Hoang 1D

I didn't even notice that, thank you guys!

Ryan Hoang 1D

Hi! I already tried to use Q=ncAT (with A =change in) to solve for C, but the value I found came out super high, and wasn't the actual answer for the heat capacity. Is there something I'm doing wrong?

Ryan Hoang 1D

Yeah, I'm really kicking myself right now. There were a couple of textbook questions that I didn't get to that ended up being on the midterm; so I got to make sure I do every single homework question and really understand it all. Also, yeah I think step-ups would be really helpful and regret not att...

Ryan Hoang 1D

At standard temperature, pKw should always equal 14, and Kw=10^-14!

Ryan Hoang 1D

I was really surprised by the amount of thermochem to be honest! I thought it would be more acids/equilibria, but it ended up being a lot of thermo which I wasn't too prepared for.

Ryan Hoang 1D

Yeah, strong acids and bases are hard to understand. But, I like to use mnemonics to help me learn:
Strong acids: So I Brought No Clean Clothes (H2SO4, HI, HBr, HNO3, HCL, HCLO4)
Strong bases: Larry Never Killed Real Cats Carly Said Boldly (LiOH, NaOH, KOH, RbOH, CsOH, CaOH2, SrOH2, BaOH2)

Ryan Hoang 1D

I think Leo answered it pretty well actually! But, yeah, that's why things like metal feel really cold to us, even though the actual temperature of the metal is about the same as other surfaces like wood. The metals can transfer heat easier, and thus feels cooler to us.

Ryan Hoang 1D

Honestly kinda weird, but I've been listening to MAX and the Weeknd a lot these days, even though they're not the best study music to be fair.

Ryan Hoang 1D

I would also recommend going back to check the values. Look at if the approximation x is less than 5% of the initial value. If so, then you can use it. If not, go back and just do the quadratic formula

Ryan Hoang 1D

You wouldn't use ICE when you are given all the concentrations AT equilibrium (in which case you'd just be able to calculate K easily). But, if you don't know the values at equilibrium and are only given initial values, you'd have to use ICE.

Ryan Hoang 1D

Yeah, I really recommend the mnemonics!
I use that same exact mnemonic for strong acids, and for strong bases, I use: Larry never killed any real cats carly said boldly!

Ryan Hoang 1D

Yeah, I think at this point, if you want to review the content, it'd be good to go back! But, otherwise, I think the first few weeks hit it pretty well as well.

Ryan Hoang 1D

ICE charts are used when we are given the initial concentrations and K or some way to find K BEFORE equilibrium. We'd use the normal K=[products]/[reactants] if we actually knew the concentrations AT equilibrium (which we might not always know).

Ryan Hoang 1D

Kc is the equilibrium constant of concentrations specifically. Kp is the equilibrium constant of gases (partial pressures). Keq=the equilibrium constant in general. Q is the reaction quotient, which is the value we get when doing the calculations for K while we're NOT at equilibrium. We can compare ...

Ryan Hoang 1D

Hi Zach! You'd have to multiply the first reaction equation by 3 to get 3H2+3I2<->6HI. If you try solving for Kc of that, you'd find that multiplying the entire equation by 3 has the same effect as cubing Ka. Then, you'd want to find another equation that you can manipulate to get the equation provi...

Ryan Hoang 1D

If we're adding two equations together, we would multiply the equilibrium constants. If we're subtracting, then we'd divide.

Ryan Hoang 1D

Yeah, just remember Kw is basically what [OH-] and [H3O+] will always multiply to, and will always equal 1.0*10^-14

Ryan Hoang 1D

Temperature often does matter, especially by lowering the value of Kp for instance, and allowing the reaction to actually occur when it would've been extremely unfavorable like with nitrogen and nitrate fertilizers. However, when it says "this reaction is at 500 degrees", you can effective...

Ryan Hoang 1D

No, anything suspended in solution as aqueous would be affected :D

Ryan Hoang 1D

Dr. Lavelle has said previously that if you have really good posts but you didn't do the posts for a week, he'd give you points back. Still, it'd be most likely best to just keep up with the 5 every week as that's simpler to do and helps to make sure you don't get in trouble.

Ryan Hoang 1D

The "Exam schedule" page on his website says that the tests are taken during class, whereas his 14A website said that it was to be taken during discussion.

Ryan Hoang 1D

Yep, that equation looks good since Kc= reactants/products (and any coefficients are exponents).

Ryan Hoang 1D

I'd recommend looking at the solutions manual on Lavelle's website. It gives a pretty clear explanation, I think. You'd be using the MiVi=MfVf (molarity initial*volumeinitial=molarityfinal*volumefinal) and to calculate the molarity. Then, find pH using -log

Ryan Hoang 1D

Sometimes, if there's something like HPO4,-2, you can just tell because it has the ability to either gain 2 electrons or lose 1 electron, so it's amphoteric. In salts, you can draw Lewis structure, or remember that typically, metals (Group 1/2) tend to form bases, while nonmetals form acids and meta...

Ryan Hoang 1D

Yeah! So, in binary acids (acids like HI or HCl), there is only one bond formed between H-Cl or H-I. This is a direct bond, so we would use size in determining acidity. The longer the bond, the weaker which allows H+ to dissociate easily. So something like HI would be stronger than something like HC...

Ryan Hoang 1D

Good luck to everyone! Hope we all do well :D

Ryan Hoang 1D

I'd just know the basics of it! Just know the stoichiometric point and understand its meaning as well as the overall shape. You never know what he could put on the final.

Ryan Hoang 1D

Jessica is right! Just make sure you look at the total charge on the molecule (if the molecule has no indication then that molecule is neutral or 0.) Add up all the charges of the ligands, and then make sure that you set the charge of the metal ion + charge of ligands= total charge. From there, you ...

Ryan Hoang 1D

It was working for me earlier today, but it seems to be down right now... Hopefully it gets back up soon!

Ryan Hoang 1D

Right, and remember, this forms a bent shaped molecule. Something good to search up is called a VSEPR chart--> it can really help you with memorizing and visualizing these details!

Ryan Hoang 1D

NH3 is a base because it gives up its two electrons especially in coordination compounds. It gives up electrons to form a bond with the metal cation, and as defined by Lewis base definition: it is a base because it gives up its 2 electrons to another acceptor compound.

Ryan Hoang 1D

Agustina is correct!
Lewis bases are those that donate the electrons, while lewis acids acccept. Bronsted bases accept a proton while the acids supply a proton.

Ryan Hoang 1D

Generally, dipole arrows move from the less electronegative to the more electronegative ion. IE: carbon--> fluorine

Ryan Hoang 1D

Honestly, I agree with the other poster. I'd just advise doing practice problems, and really visualizing the molecules that he showed us in class. Try to remember what they look like, and how they all fit together.

Ryan Hoang 1D

Remember that shape doesn't necessarily give you the amount of bonds. IE: A double bond would still be seen as one region of electrons, not two. Because of this, I'd advise to draw out the lewis structure every time.

Ryan Hoang 1D

Yep! And remember, that Sapling is also due by the end of this week :)

Ryan Hoang 1D

I'm honestly pretty confused by this too. I think he might be saying sp3 because it has a p orbital that bonds as a pi bond, but I don't really know why this would turn things from a sp2 into an sp3 (since the 2p orbital isn't a hybridized orbital to my understanding). Otherwise, I think this is pro...

Ryan Hoang 1D

Do you guys think that there will be a small curve/adjustment to grades, especially with COVID?
I'm not sure, to be honest, but it'd be really nice hehe.

Ryan Hoang 1D

Yeah, unfortunately I don't think it's super easy to memorize the bond angles. If you can visualize the yellow molecule toys that Dr. Lavelle showed us in class, that might help you distinguish between 120 degrees, or 109.5 degrees, etc. However, for a lot of the bond angles, you really just have to...

Ryan Hoang 1D

I believe that both cis-dichloroethene and trans-dichloroethene are fixed and cannot rotate because of the double bond between the two carbons. I think only single bonds are "loose" and can rotate because it is the only bond that doesn't have pi bonds. Yeah I have to agree with Jessie her...

Ryan Hoang 1D

Based on other people's posts, I'm assuming it's going to be pretty similar to our midterms! The only thing I might expect different is just more questions because I think it's going to be cumulative. But in terms of multiple choice and respondus, it's probably pretty similar.

Ryan Hoang 1D

Right! And the way I think of it is to think of Equatorial atoms like the "equator of the earth". If you look at that plane, the equatorial atoms are the ones that you would expect to be on a singular plane. On the other hand, the axial atoms are more of the atoms that stick out from the e...

Ryan Hoang 1D

Yep! Jaden is absolutely correct--> adding more electrons makes the ion more negative, which would lead to more electron electron repulsion, which would increase the size of the ion radius. This is very similar to how going across a period and increasing the amount of electrons present increases the...

Ryan Hoang 1D

While you shouldn't annotate the periodic table/equation sheets themselves, what I like to do is: if I have any comments or equations I want to remember before the test, I'll just quickly memorize them and when the test begins, jot them down on a piece of paper AFTER THE MIDTERM STARTS so that I can...

Ryan Hoang 1D

Personally, I'm kind of afraid even though last midterm was easy.
People have said before that chem can get harder, and since midterm 1 wasn't that bad, maybe this midterm will be much harder!
Just be prepared and study hard!

Ryan Hoang 1D

I agree with all the others!
Just understanding the relative bond lengths compared to each other, and how size affects bond length (bigger size--> longer bond length), or more bonds in general (single bond is larger than double bond is larger than triple bond).

Ryan Hoang 1D

I'm pretty sure they're different, yes!
Lewis acids/bases either accept or donate electrons respectively, while cations and anions are positively charged vs negatively charged!

Ryan Hoang 1D

I 100% agree with Catie! While it's easy to just memorize the direction of the arrows, I think that understanding the reasons for the trends are really important (and will take you a lot further than just memorizing the trend arrows, especially for later on if you want to take the MCAT or other test...

Ryan Hoang 1D

I agree with Organic Chem tutor--> they go over questions in good detail and provide good examples :)

Ryan Hoang 1D

Adding on some additional info you don't need to know quite yet... There are actually different defintions of acids and bases! There are definitions like Bronsted Lowry definition--> in which an acid is a substance that donates protons(H+), and a base accepts protons (H+). There is also Arrhenius de...

Ryan Hoang 1D

To be safe, I'd just recommend posting 5 times each week. That way you're on track just in case.

Ryan Hoang 1D

Everyone here is correct: but the reason why it breaks the rule and something like sulfur doesn't is because nitrogen, being n=2 only has l=1, and ml=-1,0,1. Because of this, the maximum amount of electrons that can be filled into nitrogen are the p orbitals, the px, py, and pz orbitals (2 electrons...

Ryan Hoang 1D

Hi Lucy! The d and f orbitals would be used for atoms that have higher numbers of electrons, like Silver or berkelium respectively. Typically, when doing octet rule, we don't look at these orbitals--> we use the octet rule for main group elements only, and not transition metals or otherwise. But, th...

Ryan Hoang 1D

Everyone else here is correct: just remember: formal charge gets us the most stable possible configuration of electrons. If we make FC of each atom as close to 0 as possible, we'll get more stable molecules.

Ryan Hoang 1D

Hi! so first, you have to convert the wavelength to energy, using one of the plancks constant +light energy equations. Then, you convert that value to eV (which can be found in the chemistry equation sheet). Then, you subtract the value you found with the provided .137 to find the affinity!

Ryan Hoang 1D

While the other 2 are correct, I'd like to add a way to remember the difference between cation + anion. CATions are positive, because CATs are positive :) (they lost an electron, and are thus positively charged). Anions kind of look like onions, change the a to an o, and so onions make you cry, and ...

Ryan Hoang 1D

I definitely agree with rewatching the lectures. I know it might not be popular either, but watching additional Khan academy or Organic Chem tutor videos are helpful too!

Ryan Hoang 1D

The 10^x part doesn't count because of the trailing 0s rule in sig figs. For something like 1000000, these would all be trailing 0s, so we wouldn't count them as sig figs. Subsequently, when we got to write it in standard notation, it'd be 1 *10^6, and the 10^6 wouldn't be considered sig figs

Ryan Hoang 1D

While I think Lucy explained it perfectly, I'll give you a bit more info on ml and l. For your n=5, and l=3, because l=3 equates to a f subshell, you'd know from the chart Lucy provided (and from knowing that l=0 --> s, l=1-->p, l=2-->d, l=3-->f), that there would be 7 possible answers in ml. n=5, l...

Ryan Hoang 1D

What do you get when you mix some carbon, oxygen, and a little bit of heat?

My house.

(I'm from Irvine during the Silverado fire).

Ryan Hoang 1D

I'd first recommend going over the Outlines--> they have exactly what's going to be on the test, and practice problems that are probably similar to the actual exam. Then, I'd personally recommend going over your notes again. And, if necessary, going back to rewatch lectures that you found confusing....

Ryan Hoang 1D

Yes, the amplitude is a feature of waves. Prof. Lavelle explained amplitude as the height of a wave in the ocean. A larger, taller wave has more energy as compared to a short, smaller one. Waves with large amplitudes have more energy and are brighter. Yet when we discuss the photoelectric effect, i...

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