ASAP I need Chemistry help!

audiobliss

I have some homework that's due online by midnight tonight, and I canNOT figure out two of the problems. Please don't give me answers, but I would LOVE it if you could tell me how to approach these. Nothing I've tried so far has worked out.

"Calculate the energy difference for the photon absorbed when a hydrogen atom undergoes a transition from n=1 to n=5 for 1 mole of hydrogen atoms. Answer in J/mol."

and

"An electron in the n=6 level of a hydrogen atom emits a photon of wavelength 2626nm. To what energy level does it move?"


If anyone could give me ANY advice on these, I'd GREATLY appreciate it!!!!

schwarcw

If you are expecting help from this Chemical Engineer, forget it!;)

Michael, I would search online or do some research at the library. I know you would like an answer tonight and I apologize for not being able to help. It's been 30+ years since I've been in the University.:(

audiobliss

schwarcw, no problem at all. I completely understand. Thanks for your advice, though.

I got help on the first one from a classmate and got it done. However, I'm still lost as can be on the second one.

But, if I just leave it how it is I'll still get a 91 on it. Would be awesome to start out with a 98 on the first homework assignment, but I have other homework to worry about tonight, too, so I'll settle for a 91.

RuSsMaN

You don't F with Hydrogen atoms, the answer is BOOM.

agfrost

The equation that allows you to calculate the energy of a hydrogen atom at any energy level is –(Rhc/n^2) where R is the Rydberg constant (1.0974E7 m^-1), h is Planck's constant (6.626E-34 Js) and c is the speed of light (3.00E8 m/s), and n is the energy level in question.

That said, –Rhc is a constant equal to –2.179E-18 J/atom. You'll need to multiply by Avogadro's number to convert to J/mole. (Edit: I think that should equal –1312 kJ/mol? I guess you'll still need to convert to J/mol--Pick your poison.)

Use that to calculate E for n=5 and n=1.

Energy difference is E(final) – E(initial), this should be a positive number since the electron is being boosted to a higher energy level, which requires an input of energy (deltaE is +)


What textbook are you using?

Jay


More to come.....


"Calculate the energy difference for the photon absorbed when a hydrogen atom undergoes a transition from n=1 to n=5 for 1 mole of hydrogen atoms. Answer in J/mol."

and

"An electron in the n=6 level of a hydrogen atom emits a photon of wavelength 2626nm. To what energy level does it move?"


If anyone could give me ANY advice on these, I'd GREATLY appreciate it!!!![/QUOTE]

audiobliss

Thank you SO much for that! I had already gotten the answer for the first one, but really didn't understand it. THAT made it make sense. I worked through it all and got the right answer. I didn't bother multiplying by Avogadro's number until the very end, but it worked fine.

The text we're using is Chemistry - The Molcecular Nature of Matter and Change by Silberberg, McGraww Hill, Fifth Edition. However, the homework I'm finishing up here is on WebAssign (first class I've had that uses it), but I'd imagine the questions still come from McGraw Hill.

Again, thanks SO much for that explanation! That let me see WHAT I was doing there. If you could help out with the second one, too, that would be AWESOME!

If I may ask, what do you do that you know this?

agfrost

audiobliss wrote: »

"An electron in the n=6 level of a hydrogen atom emits a photon of wavelength 2626nm. To what energy level does it move?"

Similar problem here. Only this time, you can find energy change for the emission using the wavelength, and then work your way back to what the final energy level must be. Final E level will be lower since E is released in the form of the photon.

Calculate E of the photon using E = hc/(wavelength). You'll need to put wavelength in meters first to make it work. That'll yield E in J/photon. Divide by 1000 to go to kJ/photon. Multiply by Avogadro's number to put into kJ/mol.

Now use that E (really delta E) in this equation:

Delta E = – Rhc [(1/n^2(final)) – (1/n^2(initial))]

Holy crap that's hard to type. The second thing above will be 1/36, and you need to solve for the final n^2, square root that sumbitch and you'll have your answer.

Work it from your end, I'll grab a calculator here and we'll see what we get, eh?

I'm not a chemistry teacher, but I did sleep at Holiday Inn Express last night.

...Oh wait, I am a chemistry teacher......



Jay

audiobliss

Ok, thanks so much for the info there. But I'm confused about units. If the units on -Rhc is j/atom, then why do I want to convert above to kJ/mole?

agfrost

audiobliss wrote: »

Ok, thanks so much for the info there. But I'm confused about units. If the units on -Rhc is j/atom, then why do I want to convert above to kJ/mole?

Just working with my equation list here--Let me double check for Ok-ness, I got a goofy result and not sure if it's bad equation or bad math...

agfrost

audiobliss wrote: »

Ok, thanks so much for the info there. But I'm confused about units. If the units on -Rhc is j/atom, then why do I want to convert above to kJ/mole?

Bad math by me. I'm using this eqn from my textbook that I *know* I don't like.

This will work and I think is less confusing:

We know delta E = E(final) - E(initial)

We know that the E's are (-1312 kJ/mol)/n^2.

Calculate delta E as in post 7 above, and we know that E(initial) is
(–1312kJ/mol)/6^2

Now you can solve for n final.

The cool thing about this is you know your answer has to be a whole number ranging from 1 to 5 since the electron's gotta fall...

HTH, let me know.

Jay

audiobliss

Oh wow, ok, so this was a very intense past few minutes. This homework has to be submitted via WebAssign by midnight, and it's now 12:03. I posted this same question on a Chemistry specific forum I ran across, and just received a response a few minutes ago. The guy there referenced me to the equation:



So I used that, plugged in my numbers, solved for my unknown, and got 16. I furrowed my brow as that's an energy level HIGHER than where I started from, so it CAN'T be right. Looked at the clock: 12:01. Too late anyways. Then it immediately dawns on me that I didn't take the square root of it. Well, the correct answer is 4.

Oh well, didn't get credit for that one, but at least now I know how I'm supposed to work it, I think. At least I did work it and get the right answer.

Thank you so much for your help and the time you put into posting your thoughts, agfrost. I really appreciate your input; it helped a lot.

Lemme just ask you one more question...you said, "but I did sleep at Holiday Inn Express last night." That's twice now that I've seen that...what the heck does it mean??

And, what kind of chemistry do you teach at what level? I'm finding this chemistry class to be VERY fascinating. I'm not grasping it as well or as fast as I'd like, but, I have to admit, I've really not been studying it any, either.

Again, thanks so much!

agfrost

audiobliss wrote: »

Ok, thanks so much for the info there. But I'm confused about units. If the units on -Rhc is j/atom, then why do I want to convert above to kJ/mole?

If you're using the -Rhc = -1312 kJ/mol, you want to match units. If you're using a different unit & value, just make sure the units match and all should be kosher.

agfrost

Crap, sorry I wasn't timely enough to get the job complete for you.

audiobliss wrote: »

Lemme just ask you one more question...you said, "but I did sleep in the Holiday Inn Express last night." That's twice now that I've seen that...what the heck does it mean??

Just a TV commercial series where people are doing stuff they're unqualified for but manage to pull it off due to their apparently phenomenal night's sleep they just got. I guess it amuses me...

audiobliss wrote: »

And, what kind of chemistry do you teach at what level? I'm finding this chemistry class to be VERY fascinating. I'm not grasping it as well or as fast as I'd like, but, I have to admit, I've really not been studying it any, either.

Again, thanks so much!

I teach high school chemistry, both Honors for sophs and AP for upperclassmen.

If you find it fascinating, then you're 80% of the way to where you need to be. If you feel you're not the swiftest to pick up some stuff (it'll come eventually!), worry not-- if you like it you can bulldog it into submission and your understanding will be real/more permanent than it will be for some who can cram it into short-term with some ease.

As far as the "haven't been studying it", I tell my students "you gotta do chemistry to be able to do chemistry." Hopefully since you like it, the studying will be more pleasure than punishment.

Good luck in your studies, and feel free to post or PM me with other Q's. I'm often looking for an excuse to not grade lab reports.


Jay

audiobliss

agfrost wrote: »

Crap, sorry I wasn't timely enough to get the job complete for you.

No worries at all on that front. The blame falls on me for waiting to start an assignment that's been available for at least a week 6 hours before it's due. And then having the audacity to take a supper break.

agfrost wrote: »

Just a TV commercial series where people are doing stuff they're unqualified for but manage to pull it off due to their apparently phenomenal night's sleep they just got. I guess it amuses me...

Oh, I think I saw a few of those! Haha, ok, now I get it. Don't feel quite so out of the loop now.


I bet that would be pretty fun, teaching chemistry. Gosh, I'm all over the map on what I want to do with my life...teach chemistry?! Certainly never thought of that one specifically before...but it sounds interesting enough...

Hopefully I'll muster up enough motivation to go over the material more this weekend, and if I do, I have no doubt I'll be grasping it a lot better.

agfrost wrote: »

As far as the "haven't been studying it", I tell my students "you gotta do chemistry to be able to do chemistry."

Just exactly how it is with math! And that's something I can certainly understand.

agfrost wrote: »

Good luck in your studies, and feel free to post or PM me with other Q's. I'm often looking for an excuse to not grade lab reports.

Thanks so much for your help tonight, and I'm sure I'll be looking to take advantage of it again at some point in the future!

Serendipity

I forgot all my Chemistry from Freshman year

jdhdiggs

My suggestion, take the "D" for done and drink more...

schwarcw

You two guys should get a room!;)

I have to admit, this stuff is fun. At least it was when I was in school. This looks more like P Chem or physics than general chem. Add a little calculus, and I've got wood.:cool:

agfrost

schwarcw wrote: »

You two guys should get a room!;)

I have to admit, this stuff is fun. At least it was when I was in school. This looks more like P Chem or physics than general chem. Add a little calculus, and I've got wood.:cool:

Yeah, definitely straddling the borderline between chem and physics. Makes its appearance in the atomic structure chapter of gen-chem textbooks.

Your "get a room" crack made me laugh--I did notice the thread had a "just the two of us" feel to it last night, and I admit I'm glad to see a couple others stopped in to give their respects to "The Chemistry!"


Jay

mhardy6647

Now... all I want to know... where are you guys when folks start debating the merits of esoteric cable geometries or "magic pebbles" or other such hifi snakeoil?

;-)

Serendipity

schwarcw wrote: »

This looks more like P Chem or physics than general chem.

You're scaring me - I have to take P Chem in my senior year!!

schwarcw

appadv wrote: »

You're scaring me - I have to take P Chem in my senior year!!

Of course! P Chem I and II both 4 credit hour courses. I think P Chem II has a 2 credit lab. Somewhere in that curriculum they introduce quantum mechanics, Schroedinger wave equations, molecular thermodynamics and fluid phase equlibia.

mhardy6647

thermodynamics is the easy part :-) (at least for me)
As a biochemist, I took "P Chem for Poets" when I was an UG -- not the real P Chem.

Serendipity

I'll be taking P Chem in Grad school too

Mazeroth

Chemist by day here, but outside of work I don't even want to think about it!

Serendipity

Mazeroth wrote: »

Chemist by day here, but outside of work I don't even want to think about it!

That's cool, I'd probably feel the same way...