CHEMISTRY COMMUNITY

Elizabeth Bowen 1J

The question ins to write a cell diagram, determine the standard cell potential, and calculate delta G for the reaction: Cr2O7 2-(aq) + 14H+ (aq) + 6 Pu 3+ (aq) --> 6Pu 4+ (aq) + 2Cr 3+ (aq) + 7H2O (l) How do we find the standard reduction potential for the oxidation half reaction (6Pu3+ (aq)->6Pu4+...

Elizabeth Bowen 1J

I'm confused as well. Why isn't the answer a positive value? It's because they flipped the cell diagram and put the cathode on the left when we learned that conventionally it should be on the right, my TA told me that we shouldn't worry too much about this kind of situation because they would just ...

Elizabeth Bowen 1J

If the standard cell potential of a cell diagram is negative, does that mean that the cathode was put on the left and the anode was put on the right?

Elizabeth Bowen 1J

should the standard potential at the cathode and anode of a galvanic cell always be positive (which results in negative delta G--because of delta G=-nFE), because the 1/2 reactions should be spontaneous? If not, then can someone explain why/how the reaction could be spontaneous if the standard poten...

Elizabeth Bowen 1J

In the textbook, it says that a negative standard potential means that a redox couple is more strongly reducing (rather than oxidating), but I'm a bit confused because doesn't a negative standard potential just mean that delta G will be positive, so the reverse of whatever electrode reaction we're g...

Elizabeth Bowen 1J

Why are species of the same phase separated by vertical lines instead of commas in the answer, and where do the free OH-(aq) ions come from since the original equation is only made of solids?

Elizabeth Bowen 1J

How do you calculate the Cell potential of a cathode/anode when you're given an overall reaction and are breaking it down into half reactions so that you can know which direction to write the spontaneous reaction? or should we assume that the direction of the overall reaction is already spontaneous ...

Elizabeth Bowen 1J

In 6L.7, the overall reaction given is AgBr(s) <--> Ag+ (aq) + Br-(aq) The cathode reaction given in the solutions manual is Ag+ (aq) + e- --> Ag(s), which makes sense, but the anode reaction given is AgBr(s) + e- --> Ag(s) + Br- (aq) Why it wouldn't just be Br(s) + e- --> Br- (aq), similar to the c...

Elizabeth Bowen 1J

Does it matter if when we make a balanced redox reaction whether we simplify the coefficients or not?

Elizabeth Bowen 1J

Why when we write a redox reaction from a cell diagram do we not balance it out the same way as how we learned for redox reactions in general? For example, on page 552 they have the cell diagram Pt(s) | H2(G) | HCl(aQ) | Hg2Cl2(s) | Hg(l), and they write out the oxidation reaction as 1/2 H2(g) --> H...

Elizabeth Bowen 1J

How would we know which species are on which side of this cell diagram? (it's from an example on page 552) since this example only has a porous disk, so how would we know if HCl is on the left or right side? Or does it not really matter for writing out the chemical reaction equation for this cell? P...

Elizabeth Bowen 1J

Eunice Nguyen 4I wrote:I was always told to follow (s)|(g)|(aq)||(aq)|(g)|(s). Aqueous in the middle separated by two || (salt bridge), and the solids on the outside.

Does anyone know what we would do if there's a liquid?

Elizabeth Bowen 1J

We wouldn't have to draw out a picture, we'd just have to draw the diagram where one line (I) refers to the division between species of different phases, and a double line (II) refers to the salt bridge between both sides of the sell diagram. If we have more than one species of the same phase, they ...

Elizabeth Bowen 1J

An Oxidizing agent does the oxidizing, so it allows the other side to become oxidized, and vice versa.

Elizabeth Bowen 1J

My TA told us we should always use platinum as good practice, but technically any inert metal would function.

Elizabeth Bowen 1J

We would have to determine it ourselves knowing that charge leaves the cathode and flows towards the anode.

Elizabeth Bowen 1J

it will cover the second half of gibbs free energy outline and the entire next outline after that

Elizabeth Bowen 1J

I talked to Lavelle during office hours and he said yes, 50% is a C-, and if you get something above, like 70% or something similar, it depends on the class grades when the class is over what that percentage would correlate to grade-wise, but it will most likely be higher than a C-.

Elizabeth Bowen 1J

When you break up a redox reaction into the reduction and oxidation reactions that make it up, those two reactions are the half reactions.

Elizabeth Bowen 1J

Yes, do what the other responses have said. What I've been told is that it's good not to think of Basic and Acidic Conditions as being too different, the procedure is exactly the same except for that one extra step.

Elizabeth Bowen 1J

a salt bridge just allows ion transfer so that the redox reactions can keep going on and won't run out of/build up ions.

Elizabeth Bowen 1J

I remember that the required chemistry community posts per week is 5, but I'm kind of doubting myself now because I can't find it listed anywhere on the site or the syllabus, so can someone confirm just to make sure?And can someone tell me where this info is found? Thanks!

Elizabeth Bowen 1J

question: A human body generates heat at the rate of about 100W. (1W 1J s-1) a. what rate does your body heat generate entropy in your surroundings, taken to be at 20 C Can someone explain why we're able to use delta S = q(rev)/T for this problem? How do we know that the q we get (q=100J) is reversi...

Elizabeth Bowen 1J

Will we have to have the conversion bw atmospheres and pascals memorized for the midterm? I realized it’s not on the equation sheet but some hw problems need it

Elizabeth Bowen 1J

I found this answer from chem community to be helpful: "In order to do this problem, you would first calculate the energies to break the bonds of 3 double bonded carbons and 3 single bonded carbons. You would then compare this value to 6 resonance carbon bonds, and see that the resonance struct...

Elizabeth Bowen 1J

Oh, ok thanks! Can anyone explain how the acid/base being weak or strong would influence how you write out . the reaction?

Elizabeth Bowen 1J

do any gaseous reactions ever occur at neither constant volume nor constant pressure? (so you wouldn't be able to use delta H = qv or qp)?/ how would you know when this is the case?

Elizabeth Bowen 1J

Thanks, if we were told that a gas expansion is isothermal, do you think that we should assume it's an ideal gas if not specified (so that we can use the fact that delta U=0)?

Elizabeth Bowen 1J

ok, thanks that makes sense; if we're told that there's not constant pressure, but constant temperature, that means it's reversible, correct?

Elizabeth Bowen 1J

can anyone explain why delta U=0 for an isothermal ideal gas expansion/compression?
thanks

Elizabeth Bowen 1J

If we need to calculate the work of expansion of a system, and we're not told whether it's a reversible or irreversible expansion, how do we know which equation should be used?
thanks

Elizabeth Bowen 1J

How would we model an isobaric system? I understand that an isobaric system has constant pressure, but how would the volume be changing if the pressure is constant? In the case of a cylinder with the piston, does the constant pressure refer to the pressure exerted by the piston and would we be seei...

Elizabeth Bowen 1J

you can think about it the same way as when enthalpy is positive or negative—> it’s negative if the system is giving off heat, just like if the system is doing work (or “giving off” work so to speak), and like with enthalpy, it’s positive when the system is gaining heat, or when heat is being given ...

Elizabeth Bowen 1J

The equation for change In Volume is actually delta S = nRln(V2/V1), where n is moles and R is the ideal gas constant-this equation is given on the equation sheet from lavelle

Elizabeth Bowen 1J

Could anyone tell me the general formula/way to write out an acid-base titration? (For example HBr + KOH)

Thanks

Elizabeth Bowen 1J

Does anyone know if the midterm is going to be graded by a different TA for each discussion section, or do they have uniform graders for each problem?

Elizabeth Bowen 1J

Hey, could anyone explain to me why 1 m^3=1000 dm^3? I thought that decimeters would be a difference of 10^1 not 10^3 because of its prefix

Elizabeth Bowen 1J

I don't think so either

Elizabeth Bowen 1J

Because, if you reference the graphs that lavelle gave us for reversible vs non reversible pathways, you can see that in irreversible pathways, the reaction follows two straight steps, rather than a curve. Since the two steps are straight, one is at constant volume, and the other is at constant pres...

Elizabeth Bowen 1J

Why does q (heat) need different values/symbols for qv and qp? I know that it's for constant pressure and volume, but why do these make the values of q different (why isn't it all just q)?

Elizabeth Bowen 1J

How do we know if something's a strong acid/base?

Elizabeth Bowen 1J

Intensive properties are more informative, since they are always the same for a certain substance (density), whereas extensive properties can be different for the same substance (you can have different volumes or masses of one substance)

Elizabeth Bowen 1J

Make sure to memorize the conversion between Celcius and Kelvin.

Elizabeth Bowen 1J

Does anyone know where we can find all the powerpoints from the review sessions (/if they're all posted)? Thanks!

Elizabeth Bowen 1J

I tried to go to the drop in session in covel 210 on Wednesday (feb 5th) that was supposed to be held from 7-9, but I didn't see anyone there (the room was empty), So I was wondering if someone could clarify--did anyone go to this session and it was being held? because I'm not sure if I got the room...

Elizabeth Bowen 1J

I know that we have to know how to write out combustion reactions on our own for the exam, so I was wondering if anyone could explain how to do that?

Elizabeth Bowen 1J

can anyone explain why percent ionization for hydrofluoric acid isn't just assumed to be 100% since HF is a strong acid?

Elizabeth Bowen 1J

I know how we learned that you can do an approximation when Ka is smaller than 10^-3, but I was wondering if anyone can explain how we can check if that approximation is correct or not? (because it's sometimes a gray area if it's only a little smaller)

Elizabeth Bowen 1J

I was confused by this one too on the test, because I thought that the reaction should favor the side with the least moles if pressure was increased, which is what I answered, but it wasn't correct so I was wondering if someone could explain that problem as well.

Elizabeth Bowen 1J

how would you calculate q in 4F.1? I don't understand what information we need to calculate q

Elizabeth Bowen 1J

Will we have to memorize the conversion between kelvin and celcius?

Elizabeth Bowen 1J

Have we covered section 4F in class? I realized I don't know how to do any of the problems without reading over the textbook and I don't know if I just missed something in class

Elizabeth Bowen 1J

Make sure to start studying a lot in advance so that you have time to do all the practice problems! In my experience, just reading the textbook and doing a few problems isn't enough to really solidify what I've learned, but once I do a ton of practice problems, I 'll know exactly what to do and wher...

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