CHEMISTRY COMMUNITY

GabrielGarciaDiscussion1i

Hello friends, does anybody have any tips and tricks they would like to share with group on how we can remember functional groups. Any unique thought processes or cool mnemonics that helped them? I struggle with functional groups and so anything will be helpful, thanks.

GabrielGarciaDiscussion1i

My question is a multi-part doozy, so here goes: 1) In chemistry community, I've always wondered what exactly counts as a post. Will this question count as a post even though it is not directly science related? If we ask for tips and tricks from other students on how to memorize functional groups be...

GabrielGarciaDiscussion1i

That is because the product will be gaining an increase in concentration as the reaction goes on because the anode will begin to consume the electrode and produce the Concentration ion while the cathode will be gaining mass to the electrode and consuming the Concentration ion. So in order for the re...

GabrielGarciaDiscussion1i

Yes, although be careful with your Mn^2+, it should be 2 moles of Mn^2+ and I believe that is what you meant but the notation got a little funky.

GabrielGarciaDiscussion1i

I think you mean EcellStandard, if that is what you mean, then for concentration cells, yes they should be zero. And I can't remember 100%, but yes I believe for Galvanic/Voltaic, they should be positive.

GabrielGarciaDiscussion1i

The question seems to be conceptually based with the comparison of Ecell and EcellStandard. For a, only Ecell decreases with time For b, both Ecell and EcellStandard are temperature dependent For c, Neither Ecell or Ecell* (I'm using a star for standard because I am tired of writing the standard thi...

GabrielGarciaDiscussion1i

This question was asked and answered on Chemistry community years ago and so I'll post the original link, but I'm gonna write the answer again here and fix it because it had mistakes in the terminology. https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=1577 (This answer says Br is being reduced an...

GabrielGarciaDiscussion1i

This question was asked on chemistry community quite a long time ago and there was an ENDORSED answer so I'm gonna put it here to help: A salt bridge is an inverted u-shaped tube that contains an electrolyte and allows the two half cells to be connected so ions can flow freely and the charge between...

GabrielGarciaDiscussion1i

Well remember that in order for something to be an intermediate, it needs to be produced then consumed within the elementary steps. That being said, I'm not sure it's possible to have an intermediate in a one step reaction because there would be no way to produce a substance and use it all in one st...

GabrielGarciaDiscussion1i

Do you always ignore the reverse of the slow step? Why? Well the idea is that when it comes to the slow step, the reaction produces products slowly in comparison to the other reactions so that the slow reaction can only proceed forward for a significant amount of time since there is not a significa...

GabrielGarciaDiscussion1i

Will we be told which step is the slow or fast step? If we are not told how do we find the slow step? Once again, almost positive that we will be told which step is the slow step or fast step. However, in the highly unlikely case we are not told, we can always look at factors such as Activation Ene...

GabrielGarciaDiscussion1i

It is extremely likely that we will be provided a Half-Reactions sheet , however, I doubt it will be as long or extensive because the final will be cumulative and not solely based on electrochemistry like the E.Chem test.

GabrielGarciaDiscussion1i

Intermediates appear as products and then are consumed in later steps while catalysts are present in the beginning of the mechanism, used in one of the steps, then produced so as not to be consumed in the overall rxn.

GabrielGarciaDiscussion1i

I can help LOGICALLY (and sort of mathematically), think about a firecracker. The deltaS for a firecracker exploding is extremely positive when ignited because it leads to a tremendous amount more of disorder, where S represents entropy (disorder). However, think about the reverse process, an explod...

GabrielGarciaDiscussion1i

To identify a catalyst, simply look for it in the beginning as a reactant where it is used and then if it is produced again later, it is a catalyst since catalyst are not consumed through reactions.

GabrielGarciaDiscussion1i

It's dangerous to make blanket statements of ALL PROBLEMS TO SECONDS, but usually the problem will specify with seconds, minutes, or heck, maybe even hours with LARGE half lives. So just read the question and dimensional analysis when necessary.

GabrielGarciaDiscussion1i

That equation, I believe, is given on the equation sheet. Or at least U = (3/2)nRT is given. As for the KEavg=3RT/2, I believe that's in the book and may just be something that needs to be memorized.

GabrielGarciaDiscussion1i

I believe the C in that equation may be the implied molar heat capacity. Otherwise, I am unsure exactly what that C may be or where the n comes from and will give you a bump for Chem_Mod.

GabrielGarciaDiscussion1i

One way to help determine is the the number of molecules needed to combine. So more often than not, a bimolecular reaction will be slower than a unimolecular. Then termolecular being slower than bimolecular. THIS IS NOT FOOL PROOF OR ANY KIND OF LAW TO USE 100% OF THE TIME, just something to conside...

GabrielGarciaDiscussion1i

Water is left out of the equilibrium expression because it is a liquid, and liquids have constant concentrations. Generally this means it is included as part of the equilibrium constant because it's constant anyways. The same applies for the rate constant expression. This is an extremely detailed a...

GabrielGarciaDiscussion1i

I'm very close to 100% certain we will not have to propose a reaction mechanism on the test. Lavelle has mentioned it in his lectures when he says the majority of our work will be seen in the rate laws derived from mechanisms and seeing if the mechanism rate law matches the experimentally determined...

GabrielGarciaDiscussion1i

When the temperature is higher, this leads to an increased number of collisions AS WELL AS a higher energy for the molecules so that more collide with sufficient energy to overcome the Activation Energy needed. So yes, if a higher Ea is given, increasing temperature may help to overcome it.

GabrielGarciaDiscussion1i

If it's standard reduction potential, then couldn't you just combine the two standard reduction potentials since the Fe3+ would have to go through both reductions? But then I also feel conflicted because I believe standard reduction potential is an intensive property and I believe intensive properti...

GabrielGarciaDiscussion1i

Yes, it seems as though the half reactions are the ones in the back of the book. This question seems to function a lot like Lavelle's test that had the reduction reactions in the back of the test and you had to look at them to compute voltage and understand the reaction taking place. However, I do n...

GabrielGarciaDiscussion1i

Well considering the entropy (S) is equal to Q (heat) / T (Temperature), we can then look at the differential equation of a reversible process: dS = dQrev / dT So at any infinitesimally small change, the dS that is lost by the system/surroundings is then gained into the system/surroundings because r...

GabrielGarciaDiscussion1i

I too am curious about these oxidation states, especially with the idea that we can have non-integer electrons, and so bump for Chem_Mod. The book says something along the lines of "if staying consistent, you should be fine" but I'd rather understand and ask, should we expect anything like...

GabrielGarciaDiscussion1i

IM BACK! I know there is slight confusion on balancing redox rxn's so the way that I do is: --Make your half rxn's, one for reduction and one for oxidation. --Balance anything that isn't Hydrogen or Oxygen. (DO TO BOTH HALF RXNS) --Use H20 to balance out oxygen and then H+ to balance out Hydrogen (y...

GabrielGarciaDiscussion1i

I will give you a better answer right now, but I'm simply replying so this goes to "my posts" tab on Chemistry Community and therefore I can get back to it easier.

GabrielGarciaDiscussion1i

A question similar to this was asked years ago in Chemistry Community and so I'll put this here in hopes it helps you: " Q comes from the equilibrium, that is, Q is the equilibrium quotient corresponding to the nonstandard conditions. Just like Q in other chemical reactions, Q is the ratio of t...

GabrielGarciaDiscussion1i

I too have this question, TA Tate went over a question involving these but the TA's have all mentioned they do not know explicitly what is on the test so any chance the Godfather of Chemistry, Dr. Lavelle himself, may enlighten us??
Please????? ((:

GabrielGarciaDiscussion1i

I think the same rules applies as any other ion, if they are in the same phase, use a comma and the side that they come out on depends on whether they are used in the anode as reactants or produced in the cathode as products.
HOWEVER, I AM NOT 100 PERCENT CONFIDENT SO.....
Bump for Chem_Mod

GabrielGarciaDiscussion1i

Lavelle actually posted this years ago but hopefully it helps (: G is actually defined as the maximum non-expansion work under constant T and P. Non-expansion means not related to a volume change, for example, electrical work, which is also what we call "useful work". This can be proven ma...

GabrielGarciaDiscussion1i

Yes, compression is a negative delta V, which multiplied by negative P, gives you a positive value for work.
Same methodology for expansion, positive delta V.

GabrielGarciaDiscussion1i

This question was worded a little tricky but I will try my best to answer it. The overall rate law should ALWAYS be equal to the rate law of the slow step. However, I believe what you may mean to ask is "How do we differentiate between the instances where the rate law is simply: A+B-->C rate=k[...

GabrielGarciaDiscussion1i

DeltaG's units come from the equation involving Faraday's constant
DeltaG= -nFE

E = units of volts (joules/coulomb)
n= moles
F= units of (Coulomb/mol)

So DeltaG should actually have units of J ?
Unsure how you got your units.

GabrielGarciaDiscussion1i

Almost positive it is DeltaG, not DeltaG standard

GabrielGarciaDiscussion1i

There is no specific specified side as to where to put the ( H+/OH- ). I know there is slight confusion on balancing redox rxn's so the way that I do is make your half rxn's, balance anything that isn't Hydrogen or Oxygen, use H20 to balance out oxygen and then H+ to balance out Hydrogen (you put th...

GabrielGarciaDiscussion1i

How in depth are we expected to know the derivation of and utilization of the constants Cp and Cv. Are we supposed to understand the relationship in how Cp - Cv = R ? Are we supposed to understand how these constants change with degree of freedoms? Please elaborate how greatly in depth we are suppos...

GabrielGarciaDiscussion1i

The book (and it seems Lavelle does so as well but I haven't TRULY analyzed his lectures) seems to follow the notation whenever it talks about any matters regarding enthalpy, entropy, and Gibbs free energy. Specifically, the final answer for these questions such as the Delta H = +10 kJ/mol , etc. Ho...

GabrielGarciaDiscussion1i

STATUS UPDATE: The book has been returned. Thank you all.

GabrielGarciaDiscussion1i

I put that it would only create two lines on the screen where the interference pattern existed, because they only go forward and straight through the slits, unlike waves which can diffract and experience constructive/destructive interference.

GabrielGarciaDiscussion1i

Myoglobin, Metal is Fe, and it carries Oxygen.

GabrielGarciaDiscussion1i

Hey guys, I was in Moore 100 for my final today and I left my Chemistry text book near my black Jansport backpack. However, after the test it was gone and so I'm thinking that someone may have taken it by accident. If that's the case, I promise there will be no issues or hard feelings but I would PL...

GabrielGarciaDiscussion1i

I suppose for the chemical reasoning, one could understand that a single bond is just one interaction between two atoms and that forms a sigma bond. However, with a double bond, we now introduce a pi bond which uses a p orbital to get the two atoms to bond together at two interaction sites. Then, wi...

GabrielGarciaDiscussion1i

Do me a favor.... grab your friend with one set of locked hands. Then have your other friends try to pull you away, and you'll find it's not that hard and you guys have a lot of space between you. NOW, grab the other hand and face them and have your other friends try to rip you two apart. It is much...

GabrielGarciaDiscussion1i

It means that if an extremely weak acid contributes a concentration of [H30+] < 10^-7, then the compound is still considered ESSENTIALLY neutral because with water autoprotolysis, the [H30+] is 10^-7 and then adding 10^-12 is so insignificant that the [H30+] is still essentially the same.

GabrielGarciaDiscussion1i

No, the electronegativity of an element is actually a calculated value consisting of both the ionization energy and the electron affinity. I believe what you are speaking of is the Oxidation state.

GabrielGarciaDiscussion1i

No, because pKa is the -log(base10) [Ka]. Therefore an extremely small Ka of 1x10^-10, when the -log is taken will give you a pH of 10.
So therefore a larger Ka will give you a stronger acid.

GabrielGarciaDiscussion1i

You are absolutely positive, 4 myoglobins DO make up one hemoglobin. This was a medical example that Lavelle shared with us in class.

GabrielGarciaDiscussion1i

Only one electron can have that exact set of 4 quantum numbers, someone please correct me if I'm wrong, but that is how it is with any set of 4 specific quantum numbers/

GabrielGarciaDiscussion1i

I believe you may mean in instances where K (this is a common rule, not hard fact and method) is less than 10^-3 or K is VERY small. It is in these instances that we assume X is also very small (WE DO NOT ASSUME X=0, this may be a trick question on the final so beware) to the point of being negligib...

GabrielGarciaDiscussion1i

I think K is usually assumed to be Kc unless there are partial pressures discussed within the problem (since Kp is such a specific equilibrium constant). But in order to avoid any confusion in your answers and hopefully get those MAX points ( which we all want ;D ) I would use specific notation and ...

GabrielGarciaDiscussion1i

Everyone is explaining what Endothermic and Exothermic are but here are some examples you can look up if you wanna learn more or see:

Endothermic:
dissolving ammonium chloride in water
mixing water and ammonium nitrate

Exothermic:
any combustion reaction
a neutralization reaction

GabrielGarciaDiscussion1i

Dr. Lavelle mentioned today in his lecture the various things that we should know and memorize and I do not recall him ever saying anything about specific pKa/pKb values. However, he did say that you should know that pH + pOH = 14 and that Kw= 1x10^14

GabrielGarciaDiscussion1i

This molecule would be considered polar and one way to help identify this is to look at the symmetry on the molecule. Since this molecule has a lone pair, it is not symmetrical and therefore, has a net polar movement.

GabrielGarciaDiscussion1i

Secondly, when it comes to calculating equilibrium constant, if there is ever a solid, it is excluded completely from the equilibrium constant calculation so therefore it would not affect your equilibrium when you change pressure by changing the volume. Explaining how changing the pressure changes c...

GabrielGarciaDiscussion1i

When you increase the pressure, the first question you need to ask is HOW? If the pressure is increased by noble gases, then concentration is not changed at all and the equilibrium constant stays the same. However, if the pressure is increased by a decrease in volume, then yes, you could use the mol...

GabrielGarciaDiscussion1i

One trick that I use, although it may not be "educated", is look for Nitrogen molecules. If the nitrogen has only 3 bonds, this means it has a lone electron pair that can serve as a binding site. Next, look for Oxygen molecules that are single bonded and have a negative 1 charge and these ...

GabrielGarciaDiscussion1i

I believe that if you write out the full name, it can only help you instead of hurt you because my TA discussed in our section that he wasn't fully sure but that it's probably safer if you write out the whole ligand. However, whatever you choose, the idea is that you remain consistent as with most l...

GabrielGarciaDiscussion1i

Yes, they are both two sides of the same coin. Bronsted focuses more on the proton while Lewis focuses more on the exchange of an electron. Maybe this will help, but one pneumonic/funny way I tend to remember it is that "Lewis Acids LOVE Accepting electron" (The LA , LA pattern is fun for ...

GabrielGarciaDiscussion1i

Absolutely, when determining the strength of acids and bases, you can use electronegativity as one of the indicators when it comes to electron withdrawing groups. Some of the other indicators you should use are: ----The length of the bond between the proton and the acid ----The number of resonance s...

GabrielGarciaDiscussion1i

The answer to part b would also be yes, BF3 has an incomplete octet and an empty 2p orbital, so it can accept a lone pair. So clearly BF3 is a Lewis acid as it can accept a lone pair. As for part C, one could infer that Ag+ would want to accept the electron because of its overall positive charge tha...

GabrielGarciaDiscussion1i

I believe the answer to question A would be yes, since Nitrogen has 5 valence electrons and since it is only bonded to 3 hydrogens, that leaves one lone pair of electrons.

GabrielGarciaDiscussion1i

Can someone, in a hopefully somewhat simpler and not extremely complex or technical manner, explain to me how a double bond between two atoms is considered a sigma bond and a pi bond when pi bond is two interactions between two p-orbitals that are parallel to each other? The fact there are two inter...

GabrielGarciaDiscussion1i

Hey guys, I'm still a little confused as to why increasing the pressure with a noble gas does not affect the reaction quotient? In my head, I see it as increasing the number of people in a room that contains two different groups. By increasing the number of people in said room, how does this not aff...

GabrielGarciaDiscussion1i

Yes, it is incredibly important that you include lone electron pairs because as seen in different geometric shapes, the lone pairs influence the shape through electron repulsion. HOWEVER, when determining the molecular geometry, one often only considers the regions of electron density that exists as...

GabrielGarciaDiscussion1i

On the topic of the polarity as a whole, CCl2 would be considered non-polar because the electronegativity vectors cancel out but be careful because, as seen on the midterm, there is a distinction between the overall polarity and the polarity of the individual bonds. The bonds are polar, but the over...

GabrielGarciaDiscussion1i

In agreement with the comment above me, while it may not be REQUIRED of us, it can only benefit you to begin to at least become familiarized with poly-atomic ions, compounds, and begin to work your way around nomenclature. Some examples may be understanding the differences between sulfate and sulfit...

GabrielGarciaDiscussion1i

We haven't fully got into Electronegativity yet but as we began to touch on it in today's lecture, Oct 30th Monday lecture, it is my understanding that Ionic bonds see a great difference in Electronegativity where one element in the bond is significantly more Electronegative (meaning it's delta is g...

GabrielGarciaDiscussion1i

My question is in 2 parts,
1) Since test 3 covers the remaining sections of chapter 1 and all of chapter 2, is there a preferred homework section that Professor Lavelle would like us to focus on?
2) When is our test date for Test 3?
Thank you.

GabrielGarciaDiscussion1i

Good very late night, I had a question regarding the homework and what exactly we should do this week. I was not fully quite sure where to post it, so I tried Quantum Mechanics since we are entering that in lecture. I understand that we started getting into the Quantum world with Monday Oct. 9 Lectu...

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