college chemistry help....

me2gud4u

is there anyone out there able to help me with these chemistry questions??Here are some of them

the decomposition of N2O5 to N02 and O2 is first order reaction with a rate constant of k=4.80*10^-4s^-1 at 45 degrees celsius.

1)if the initial concentration of N205 is 1.65*10^-2moldm^-3 what is the concentration after 825 secs?

2)how long would it take for the concentration of N205 to decrease to 1.00*10^-2moldm^-3 from its initial value of 1.65*10^-2 moldm^-3

if anyone is able to help me with this i would be so greatful...... there are a few more but i just wanted to see if anyone could help me with this one first.

dubred

The best person to help you would be the lecturer, that's what they are there for, go knock on their door and ask them if they have some time for you, you might be pleasantly surprised at how helpful they can be.

stereoroid

This question looks awfully familiar...

It's a first order reaction, so you basically need to memorize and manipulate the formula for its rate constant: ln ( [A]0 / [A]t ) = kt
[A]0 = initial concentration, [A]t = concentration at time t

In part 1 you have everything but At
In part 2 you have everything but t
In the exam, watch out for the wording: "decrease by" vs "decrease to" - this is "decrease to" so the formula works as is.

me2gud4u

thanks!!

mmmm do u think if i posted a few more questions you could explain to me how ya do them?!

woop

looks fairly familiar to me aswell:rolleyes:

me2gud4u

pre meds?!

stereoroid

me2gud4u wrote: »

thanks!!

mmmm do u think if i posted a few more questions you could explain to me how ya do them?!

You'd be better off going to the Library, getting out one of those undergraduate chemistry books filed under 540, and just reading a few chapters. I did that today, and had no trouble going back over the revision questions. Except for Q7: when the Calculus comes out, my eyes glaze over...

Le Rack

First year questions? So glad I said good bye to all that...

How did you guys find it in general? I wasn't able to keep up with those calculations at all, and detested calculussy stuff!

stereoroid

Found the first half generally OK, basic chemistry that was largely revision for me, but the second half has gone in to major depth on chemical reactions, rate constants, and even catalysts. This is one of two courses for which I can say, with reasonable certainty, that I won't need that level of detail ever again. I'd rather have had electives instead - I'd have chosen in-programme courses more relevant to what I'm actually here for. :rolleyes:

Le Rack

I had to do chemistry, and had to do intro, cuz I didn't make the grade in the LC to do chem..summit or other, but they claimed for intro that you didn't need any prior knowledge of chem, and granted for the first few weeks it was like being back in junior cert, and I was teaching my mates stuff, within about a month and a half to two months it was gone way over all our heads and the stuff we'd gone on to, I knew you would have to have a prior knowledge of chem to do, it was a bit ridiculous really...

woop

wait for wigidy wagidy waghornes phys chem in the second semester youre gonna love it:p


are they not doing chem tutorials for ppl to go and ask Q's?

stereoroid

woop wrote: »

are they not doing chem tutorials for ppl to go and ask Q's?

Not for the course the OP and I were on: Chemistry for Engineers. Just lectures and some in-lecture multiple choice tests.

Le Rack

woop wrote: »

wait for wigidy wagidy waghornes phys chem in the second semester youre gonna love it:p


are they not doing chem tutorials for ppl to go and ask Q's?

ah yes, waggleyhorn as one of my mates called him...I failed that rather miserably

lizzyvera

When I and another rep went to talk to him about the fail rate he said "I didn't fail half of phys chem- half of phys chem failed me!". He's MUCH better this year, he's terrible at explaining easy things. Use the book and do the problems in it. I wish I hadn't bothered with lectures.

Le Rack

lizzyvera wrote: »

I wish I hadn't bothered with lectures.

em...I think thats where it all went wrong for me tbh...
I started out going to lecs but it just boggled me more so I stopped going...

I think he gets flustered over things and hence things go bog arse ways...

tywy

stereoroid wrote: »

Found the first half generally OK, basic chemistry that was largely revision for me, but the second half has gone in to major depth on chemical reactions, rate constants, and even catalysts. This is one of two courses for which I can say, with reasonable certainty, that I won't need that level of detail ever again. I'd rather have had electives instead - I'd have chosen in-programme courses more relevant to what I'm actually here for. :rolleyes:

You like moaning about engineering, eh? You do all these subjects in first year to give you a broad base for whatever you go into later. Engineers usually work in a team. If one in the team is a chemist, it's good to have a vague idea what they're going on about. I'm in Elec and for my final year project there is some biology involved, some kinetic equations, having done chemistry in 1st year helped me with those equations. You're in first year, you have no idea what you're going to come up against between now and finals. Which type of engineering are you doing?

stereoroid

tywy wrote: »

You're in first year, you have no idea what you're going to come up against between now and finals. Which type of engineering are you doing?

No, I don't like moaning, and I've been giving courses the benefit of the doubt all along. I'm all for keeping an open mind, and it took a lot for me to consider saying anything. I'm on a specialist track, not the ME or Omnibus tracks. I've already spoken to the programme director about my concerns, so you don't need any more info about me. Let's just say that while I may be a 1st year at UCD, I left school long ago.

With "Physics for Engineers" in particular, these statements of yours would have made sense last year, but this year the course has been changed to suit the lecturers, to the point where the old exam papers are no use. The same is true of "Chemistry for Engineers" to a lesser extent.

tywy

Are you going to do Elec or Mech or what?

And just cuz you're a mature student doesn't make you better than anyone else in the class...

They make you do these subjects for a reason!

Mutant_Fruit

stereoroid wrote: »

this year the course has been changed to suit the lecturers, to the point where the old exam papers are no use. The same is true of "Chemistry for Engineers" to a lesser extent.

So what? If courses change, you deal with it. If you can't deal with it, then either

A) Drop out, or
Talk to your classmates to find out what's useful, or
C) Talk to your lecturer

Out of the 5 finals i'm sitting this christmas, exactly 0 of the past papers directly represent any of our current courses:
Control theory - completely revamped course
Optical Engineering - three courses merged into one
Analogue electronics - two courses merged into one
Wireless Communications - two courses merged into one
Digital Signal Processing - two courses merged into one

We're coping fine with those massive changes, surely you can cope with the little changes you have.