CHEMISTRY COMMUNITY

AJForte-2C

Melissa Solis 1H wrote:What role do catalysts and enzymes play when the rate of the reaction is independent of [R]?

I think that a lot of zero order reactions involve catalysts/enzymes that make the rate of the reaction independent of [R], so the reaction can only go as fast as the catalyst allows it.

AJForte-2C

JustinHorriat_4f wrote:Does decrease temperature increase the rate for an exothermic reaction?

I believe that an increase in temperature means higher reaction rates for both endothermic and exothermic reactions.

AJForte-2C

I think we usually talk about the speed of a reaction in comparison with another or if the reaction needed to be completed within a certain time. For this reason, not 100% sure though, the speed of a reaction is just relative to the situation and its context.

AJForte-2C

today in lecture we learned about how first order reaction rates have the formula ln[A]= -Kt + ln[A(0)] and are similar to y=mx+b. The jokes about it are funny, but we gotta draw the line somewhere.

AJForte-2C

kinetics has to do with the speed at which a reaction takes place, so it would make sense that something that is kinetically stable because of the rate at which the reaction happens. Dr Lavelle gave the example of diamond turning into graphite during lecture. The reason this is kinetically stable is...

AJForte-2C

I think eventually it will happen, but I'm pretty sure that it wouldn't be observable.

AJForte-2C

I believe you would just use the coefficients from the formula. In other words, if you have aA -> bB + cC you would use the coefficients as the fractions. If a and b were both 2 and c was 3 then you would be able to find a common factor that you could multiply them all by to find these fractions fo...

AJForte-2C

we know that the rate at which products decrease and reactants increase is dependent on the specific reaction, so taking the early rates allows us to get the maximum rates for each unique reaction and compare them to other reactions.

AJForte-2C

By dividing by two we can use a general rate law for all rxns that looks like:

aA ----> bB + cC

$-\frac{1}{a}\frac{\mathrm{d[a]} }{\mathrm{d} t}=\frac{1}{b}\frac{\mathrm{d[b]} }{\mathrm{d} t}=\frac{1}{c}\frac{\mathrm{d[c]} }{\mathrm{d} t}$

AJForte-2C

Q: Why does Santa's house dissolve in water?

A: because it's polar

AJForte-2C

I think we should know the basic rules like for oxygen and hydrogen, but I would ask your TA. I'd imagine it's fair game on the final, but it couldn't hurt to check.

AJForte-2C

do ionic compounds have the same oxidation numbers as their charge or is that only for an ion by itself? Sorry, Im still kinda confused with oxidation numbers. If someone could help that would be great!

AJForte-2C

We learned that too! We also learned "Red cat, an ox" to remember that reduction happens at cathode and oxidation happens at the anode. Not an acronym, but a helpful mnemonic. Hope this helps!

AJForte-2C

E is not a state function. You can remember the state functions with the nemonic:

When you're Depressed and under Pressure, all you'll want to do is watch TV and get HUGS.

where
D=density
P=pressure
T=temperature
V=volume
H=enthalpy
U=internal energy
G=gibbs free energy
S=entropy

AJForte-2C

I have a hard time with this too and have an explanation for max potential in my mind that may help (it's not super scientific so hopefully this isn't wrong). When the switch is open (and current is 0) there aren't any actual electrons flowing but they are built up and have the potential to flow if...

AJForte-2C

ions are charged so they would be attracted to stuff with opposite charge. The bridge completes the electrical circuit between to half cells without mixing the solutions but if the salt bridge allows for free movement of ions between the half cells, wouldnt the solutions end up mixing? Sorry I'm st...

AJForte-2C

The way I like to think about it is that although they're not all technically the same thing, half reactions occur at/with the different electrodes. The overall cell is where the whole reaction occurs. So if it helps to think of the two electrodes representing the whole reaction and the cell represe...

AJForte-2C

This equation relates K (both Kp and Kc) to temperature. So any time a problem is asking about one of those in relation to each other, it's probably a good indication to use it.

AJForte-2C

I could be wrong but I remember it being on the equation sheet for test 2? but otherwise it isn't on the current online equation sheet. Although the test is open notes so just make a note of it. Hey! I didnt see it on the equation sheet. If you find an updated equation sheet would you mind posting ...

AJForte-2C

I think youre just supposed to use the Van't Hoff equation in your analysis as you usually would. I think it's just the way it's worded, and there's no actual difference between chemistry Van't Hoff and Van't Hoff

AJForte-2C

Yes, I would agree. Because there are more positions that COF2 can have compared to BF3, the residual/positional entropy of the molecule would be higher. This would also make the molar entropy higher as well.

AJForte-2C

Xinying Wang_3C wrote:
AJForte-2C wrote:are states/micro states/atomic states all basically the same thing when calculating degeneracy?

I think they are basically the same thing, just different names used in different circumstances.

thanks so much! Just wanted to make sure.

AJForte-2C

I know in lecture he said that it could be used for calculating k at different temperatures if standard enthalpy is known, but can anyone give some more specifics on how to find other variables with this equation?

AJForte-2C

are states/micro states/atomic states all basically the same thing when calculating degeneracy?

AJForte-2C

Enthalpy (delta H) is the amount of heat in a system, where as entropy (delta S) is the measure of "disorder" in a system. Both are state functions and are things that we usually measure in order to determine spontaneity.

AJForte-2C

here's a super short and helpful video on the 3rd law and how it relates to entropy:

https://www.rigb.org/christmas-lectures ... -third-law

hope this helps!

AJForte-2C

So a process is said to be reversible if you can use the same amount of work generated by the system to put it back into its initial state. When you are in an irreversible expansion, you need to put in additional work on top of what has been generated by the system to put it back into its initial s...

AJForte-2C

The difference between the two equations is that in the first one, you use mass in grams, but in the second one you use number of moles. The equation you choose will depend on what the problem is asking. how do you determine which equation to use? I believe it depends on whether you're trying to fi...

AJForte-2C

you should end up with the same answer in the end, but you'll probably get a problem that will either tell you which one to use, or you'll have to figure it out by the contextual information given by the problem. Hope this helps!

AJForte-2C

Having S=0 will never occur in reality. Theoretically it would occur in an object/system that it is at absolute 0, and is in a perfect crystal. This would mean that it would have no residual entropy.

AJForte-2C

Faaizah Arshad 1H wrote:The difference between the two equations is that in the first one, you use mass in grams, but in the second one you use number of moles. The equation you choose will depend on what the problem is asking.

how do you determine which equation to use?

AJForte-2C

So a process is said to be reversible if you can use the same amount of work generated by the system to put it back into its initial state. When you are in an irreversible expansion, you need to put in additional work on top of what has been generated by the system to put it back into its initial s...

AJForte-2C

this is because a change of one degree K is equal to a change of one degree C

AJForte-2C

heat capacity is how much energy it takes to heat up a substance by one degree C, specific heat is how much energy it takes to heat up one gram of a substance by one degree C.

AJForte-2C

Hi! Going off of this, is there such thing as an imperfect system? Would that be a system that does not fit the rule stated above? I think an imperfect system is most (if not all) systems in the real world. In order for a true perfect system to occur, maximum efficiency would have to be achieved. I...

AJForte-2C

Partial pressure only applies to gases, so youll only solve for Kp when youre being asked about gases.

AJForte-2C

I think because the conversion is so close we just say that it is 1:1

AJForte-2C

Does anyone use the textbook to study for tests? If you do, how and what parts of the book do you use?

AJForte-2C

you can think of an endothermic reaction as the system you're viewing "gaining" enthalpy or heat. This would mean that your △H is positive.

AJForte-2C

Steam burns more, because there is more energy in the steam compared to water at the same temperature. This is because water has a high enthalpy of vaporization.

AJForte-2C

I would first start with making an ICE chart and solving for the initial molarity of 2SO3 by dividing the given moles by the given volume. Then you can start filling out your ice chart. The question gives you the final moles and by dividing that by the 3 L, you get the change in molarity/x. With th...

AJForte-2C

For this question, I used Ka and Kc. I tripled Ka which is 3(H2+I2->2HI) and Ka^3 and also becomes [HI]^6[N2]/[NH3]^2 and used the reverse of Kc which only changed the Kc value 1/Kc and becomes [N2][H2]^3/[NH3]^2 then i multiplied them together which created [HI]^6[N2]/[NH3]^2[I2]^3 and is Ka^3*1/K...

AJForte-2C

I would first start with making an ICE chart and solving for the initial molarity of 2SO3 by dividing the given moles by the given volume. Then you can start filling out your ice chart. The question gives you the final moles and by dividing that by the 3 L, you get the change in molarity/x. With th...

AJForte-2C

I'm having ICE table troubles too. Can anyone recommend helpful practice problems?

AJForte-2C

This is how I solved it. First I converted mol SO3 to molarity (0.980/3.00 L) Then I set up an ICE box table SO3 SO2 O2 I (0.980/3) 0 0 C -x -2x -2x E (0.98/3)-x 2x (0.130/3.00) Then I used this to solve for X and input into the equilibrium quotient (([SO2]^2)([O2]^2))/[SO3] wouldnt the change be -...

AJForte-2C

adding helium does change the pressure, but the volume doesnt change so the equilibrium doesnt change

AJForte-2C

I think for now we just need to know the general effect a temperature change will have on a K value, and not the exact effect.

AJForte-2C

I understand the relationship between Q and K, but can someone tell me why/when we would want to measure the Q/when it would be important?

AJForte-2C

I think technically we are only supposed to use PV=nRT when we are dealing with ideal gasses/gasses that molecules that have elastic collisions. But, I think we just assume the gas is ideal if we are supposed to use it in a problem. Hope this helps!

AJForte-2C

I think whatever feels right for you to get a good grasp of the material. For me, it usually changes around exam times too.

AJForte-2C

I didn't realize how helpful the UA sessions were until I began studying for the final. I will definitely attend those more regularly during the next quarter.

AJForte-2C

I had the same exact question! How can you can you find the pKb with the given info?

AJForte-2C

Yes, strong acids form wake conjugate bases and strong bases form weak acids, the same goes for the inverse of each.

AJForte-2C

you should try taking different classes/GEs in areas of study that you might be interested in. I think the more you try different things, the more you'll get an idea for what you want to do.

AJForte-2C

meditation and positive affirmations always help me get my nerves under control in the minutes leading up to a test.

AJForte-2C

almost_ethan wrote:So are the midterms curved too or just the final grade?

I believe that the final overall grade is the only thing that is curved, not the midterms or final. Its not determined until after the quarter is done.

AJForte-2C

Another helpful note is that I learned in a UA worksop is that if you are trying to determine the stability of anions that are all within the same group, the stability increases down a group because the charge is "diluted" more in larger atoms. I believe this only holds true if you are lo...

AJForte-2C

does anyone now the breakdown of the final? Like what portions will be predominately featured etc.

AJForte-2C

Fluorine is extremely electronegative, so it's much harder for it to dissociate. This means it's considered a weak acid, because acid strength is determined by their ability to dissociate in water.

AJForte-2C

FionaHunter21 wrote:Is the acid itself being more electronegative make it a stronger acid or is it the conjugate base ?

It makes the acid more likely to dissociate, because its conjugate base is more stable. So in a way it's both. Sorry if that's a little confusing.

AJForte-2C

I think that there technically an acid can have a negative pH, but I dont think it will be addressed in this class.

AJForte-2C

ZevMarx-Kahn3C wrote:Is this a topic that will be relevant in 14B?

I think that it will, but I think this would be more relevant for a biochem/Ochem class. Hope this helps!

AJForte-2C

Is it possible for us to go over which specific questions we got wrong with our TA's? That's usually what helps me study and go over my mistakes but I'm not sure if it's too late by now I think this upcoming week is the time to go to office hours/review sessions for TA's. I think most if not all of...

AJForte-2C

The textbook problems have been super helpful, also if you're in AAP the PLF sessions have been super helpful on the midterms. I'll probably study similarly to how I did for the midterms for the final.

AJForte-2C

Does anyone know where to find any practice problems outside of the the book and sapling homework? (preferably with an answer key/explanation)

AJForte-2C

does anyone know if the class average has negatively affected grades? For example, is it possible to be passing the class as of now, but fail it in the end due to a high class average?

AJForte-2C

Because a lone pair has more repulsion power than a bonding pair, you would end up with a bent shape with either one or two lone pairs on the central atom.

AJForte-2C

Hi! I would really recommend using the website below. Its an interactive simulation where you can play around with adding different combinations of single, double, and tripple bonds, and lone lone pairs. It gives you molecular, and electron geometry. Hope this helps! https://phet.colorado.edu/sims/h...

AJForte-2C

lone pair e- do count as their own regions of electron density, including when you are creating a VSPER model. In addition, e- are more repulsive compared to bound atoms, which in turn affects the bound angles of a molecule.

AJForte-2C

Hello! I think that was just an example of one of the different ways that orbitals are hybridized when bonding in order to "free up" electrons. Im pretty sure it can happen with other orbitals as well.

AJForte-2C

Do you need to create an afbau diagram in order to properly determine hybridization, or is it not necessary?

AJForte-2C

Yes, I think because NF3 has the lone pair in addition to three bonds it occupies another axis. Whereas BF3 only has the the three bonds, so it only occupies one axis.

AJForte-2C

If lone pairs have more repulsion power than a bond, how does a lone pair affect the bonding angles of a molecule? How would we calculate it?

AJForte-2C

A bent shape can have either one or two lone pairs on central atom.

AJForte-2C

Hi, it confuses me too. Can anyone tell me how to determine the electronegativity of atoms? Electronegativity is really just determined by periodic trends. Meaning the farther right you go in period, the more electronegative and atom will be, and the farther you go down a group the less electronega...

AJForte-2C

I thinks this midterm is going to be less math based, so how are you guys studying for it?

AJForte-2C

A coordinate covalent bond is formed when one atom donates a lone pair of electrons to another, essentially providing both necessary electrons for the covalent bond.

AJForte-2C

This is because this is the only way for the molecule to achieve a charge of 0, which is the most stable state.

AJForte-2C

Yes, all coordinate covalent bonds involve Lewis bases, but not all Lewis bases involve coordinate covalent bonds. Hope this helps!

AJForte-2C

although OH- is a Lewis base, it does not form a coordinate covalent bond when bonding with a H+ ion. This is because in order for a coordinate covalent bond to form the anion needs to have a lone pair that will bond to an empty bonding region of the cation.

AJForte-2C

Midterm 2 will not be cumulative and will cover the rest of outline 2 and probably some or all of outline 3. It should be during week 3. Hope this helps!

AJForte-2C

I don't think you would be able to calculate the radius of if you have just one atom, but i believe that you can find most single atoms' radius because they have already been experimentally determined i.e. they're already known.

AJForte-2C

hello, im not totally sure, but what i remember form high school chem is that metals with a low ionization energy have electrons that are easier to move around, so in something like a galvanic cell the electrons can move around and be transferd easier, meaning it makes creating a current easier.

AJForte-2C

Oxygen has a lower ionization energy than nitrogen and fluorine, because it has one unpaired electron that is being repelled by the other electrons. This means that it is more willing to give up its first valence electron than nitrogen and fluorine.

AJForte-2C

the 3d level is a lower energy level than the 4s, because once the shells get farther from the nucleus and subsequently closer together the shells can kind of overlap in a way that makes the subshells of some of the shells in a lower energy higher than those of a subshell in a higher energy. Hope th...

AJForte-2C

It's probably important to note that they are all metals just to remember that they all have very similar properties. I think this will become more important when we start talking about ionic bonds, because the metals in the first two groups will often form ionic bonds with elements in the p-block.

AJForte-2C

[Ne} is just shorthand for 1s^2, 2s^2, 2p^6, if youre looking at a periodic table you can start at Neon and move your way down the periodic table, counting a new element for each electron. Hope this helps!

AJForte-2C

I like to do practice problems, re-writing notes, and making flashcards. These things tend to help me remember things best long-term.Hope this helps!

AJForte-2C

Something I find helpful is to use a periodic table when working with quantum numbers and orbitals. Each row on the periodic table represents a new quantum level (row one is n=1, row two is n=2, row three is n=3...etc) from there you can look at each block and figure out where the electron is based ...

AJForte-2C

the solution is 2, because the range of (+/-) 1 is the uncertainty, making 2 the uncertainty.

AJForte-2C

I was not able to attend Dr.Lavelle's discussion sections. Could someone tell me what parts of the outline will be covered? Do we need to know stuffs about orbitals and Schrodinger's equation? Dr. Lavelle sent out an email on 10/21 that said: "Midterm 1 covers material up to Wednesday of Week ...

AJForte-2C

Delta E is always negative because you are measuring the change in energy of the excited electron not the initial energy of the photon that excites it, meaning that its change in energy is negative to show that the electron goes back to its ground state after being excited.

AJForte-2C

No, when an electron is in an excited it state it is also unstable. Eventually the electron will have to revert to its more stable position.

AJForte-2C

I ended up getting one on amazon for like $20. My TA also said that you can just join the zoom with another device instead of having a webcam.

AJForte-2C

The intensity of light is determined by the amplitude of its wave (the higher the amplitude the higher the intensity). Where as the energy of a wave of EMR is determined by its frequency(the higher the frequency the more energy per photon the light has). The way I like to remember it is that the &qu...

AJForte-2C

I usually take notes on lecture and add to them when I read the book. The things that come up in both lecture and the textbook I usually make flashcards to help me study later on.

AJForte-2C

Does anyone have good tutoring options now that we're gonna be online for the rest of the semester and most likely the rest of the year? Preferably for students not in westwood/on campus.

AJForte-2C

Is there any way to keep track of how many times you have posted on chemistry community? Also does anyone know if posts on chemistry community roll over to the next week, or do I need to post 5 new posts every week?

AJForte-2C

How helpful are Dr.Lavelle's office hours for reviewing high school chem topics? What happens in them? Are there a lot of students in them?

AJForte-2C

I'm still a bit confused on how we get the E-book. After ordering through the UCLA Store, and getting the access code for Sapling, is the E-book just a link for the pdf file that also comes in the mail (or through email in recent cases) or is it accessible through Sapling? Once you get your login f...

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