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Topic: Enthalpy Assistance Please  (Read 19288 times)

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lisabella3686

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Re:Enthalpy Assistance Please
« Reply #15 on: July 04, 2005, 08:17:06 PM »
Well there's a simple way to tell which is right.  Is the reaction exothermic or endothermic?

PS: Finally found another Ontarian! (although he referred his fellow Ontarian as "the other guy" ;))

YAY! Ontario! Is this site mostly american or canadian?

Offline Mitch

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Re:Enthalpy Assistance Please
« Reply #16 on: July 04, 2005, 08:22:51 PM »
Its an international forum, although most of the admins live in California.
« Last Edit: July 04, 2005, 08:23:30 PM by Mitch »
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lisabella3686

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Re:Enthalpy Assistance Please
« Reply #17 on: July 04, 2005, 08:28:38 PM »
Nice! international is good.

I am going to go study for my exam. Thank you again for your help. I shall return later.

Good Evening

Offline lemonoman

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Re:Enthalpy Assistance Please
« Reply #18 on: July 04, 2005, 08:31:32 PM »
Yay Ontario. lol...

I'm going to Tim Hortons to help some girls with Analytical Chemistry.

I live to give.  ;D

I'll be back to answer any questions on this thread.  It's my favorite.  :)

lisabella3686

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Re:Enthalpy Assistance Please
« Reply #19 on: July 04, 2005, 08:37:45 PM »
Yay Waterloo!
I go to Western, but I am taking this course through Athabasca U. through independant study.

If you guys can band together and try to find out how the answer is -240, I would greatly appreciate it.

thanx mucho.
I'll check back in a while

arnyk

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Re:Enthalpy Assistance Please
« Reply #20 on: July 04, 2005, 08:58:24 PM »
Sweet I work at Timmie's!  Although I might be selling out if this Staples thing goes through.  ;)

Offline lemonoman

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Re:Enthalpy Assistance Please
« Reply #21 on: July 05, 2005, 03:01:28 AM »
Okay Lisa, you owe me BIG on this  :D

But here we go.  I made a mistake  ;D

Go to my huge-*ss post above, with all the reactions, and you'll notice,

Reaction 5: 2 H2 + O2 --> 0 CO2 + 2 H2O -- {H} = -286 kJ/mol

This isn't really true.  It should be -286 kJ/mol of H2...so...

Reaction 5b: H2 + 1/2 O2 --> 0 CO2 + 1 H2O -- {H} = -286 kJ/mol H2
But since we need 2 mols of H2, then
Reaction 5c: 2 H2 + O2 --> 0 CO2 + 2 H2O -- {H} = -572 kJ/2 mol H2 = -572 kJ/mol O2

Note how we just slid in a single O2 for 2 H2.  We can do that, because it's in the equation (like a titration)

Reaction 2: C +  O2 -->  CO2 + 0 H2O -- {H} = -394 kJ/mol
is fine.  One mole of O2.  We're cool.

Now comes a tricky part again  :P
Reaction 4: 1 CO2 + 2 H2O --> CH3OH + 3/2 O2 -- {H} = -(-726) kJ/mol = 726 kJ/mol CH3OH

So {H} = 726 kJ/(1 mol CH3OH) = 726 kJ/(3/2 mol O2) = 484 kJ/mol O2


That each of the equations has O2 in it.  So we'll use O2 as the main compound thing.  Units are important, keep that in mind.

Anyways, we now have
Reaction 2: C +  O2 --> CO2 + 0 H2O -- {H} = -394 kJ/mol O2
Reaction 5: 2 H2 + O2 --> 0 CO2 + 2 H2O -- {H} = -572 kJ/mol O2
Reaction 4: 1 CO2 + 2 H2O --> CH3OH + 3/2 O2 -- {H} = 484 kJ/mol O2

TOTALLY notice that each is in terms of kJ/mol O2 - before we had the one reaction in terms of kJ/mol H2 and the other one...and that's not the same unit.  So you can't add them together.

NOW when you add up the numbers you get

(484 kJ/mol O2) + (-572 kJ/mol O2) + (-394 kJ/mol O2) = -482 kJ/mol O2

Which is for C + 2 H2 + 1/2 O2 --> CH3OH

And so, again with the conversion:

-482 kJ/(mol O2) = -482 kJ/(2 mol CH3OH) = -241 kJ/mol CH3OH

Which is your answer.

P.S. It is less important to note that: (726) + (-394) + (-286) + (-286) = -240
But this is NOT the correct way to do it.

P.P.S. Did you know that here at Waterloo, we have T-Shirts that say, "Friends don't let friends go to Western"?   ;D  - They might be all over the place.  Maybe even at Western  :P

Offline Mitch

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Re:Enthalpy Assistance Please
« Reply #22 on: July 05, 2005, 01:44:57 PM »
Sweet I work at Timmie's!  Although I might be selling out if this Staples thing goes through.  ;)

Did you know that those of us who are south of the border don't know what Tim Bits are, but I do. ;)
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arnyk

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Re:Enthalpy Assistance Please
« Reply #23 on: July 05, 2005, 03:00:19 PM »
Well then you must be very cultured indeed eh?  I think Wendy's bought Tim Hortons a couple years back though so once again an American company takes over a successful Canadian enterprise. ;)

Offline lemonoman

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Re:Enthalpy Assistance Please
« Reply #24 on: July 05, 2005, 03:18:48 PM »
From the Wendy's Internation Website:

"There are more than 2,400 Tim Hortons restaurants in Canada and more than 250 in the U.S. Founded in 1964, Tim Hortons merged with Wendy's International, Inc. in 1995."

Let's see...32 million people in Canada...2400 Tim Hortons...that's one for every 13000 people.  Seems like a lot more though  :P

AND there's 250 Tim Hortons in the US?  Since when?

It won't be long before Walmart buys them all out anyways.

arnyk

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Re:Enthalpy Assistance Please
« Reply #25 on: July 05, 2005, 03:25:10 PM »
Funny how they say "merged" when Ron Joyce clearly completely sold out for $450 million (CDN ;)).
« Last Edit: July 05, 2005, 03:25:30 PM by arnyk »

lisabella3686

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Re:Enthalpy Assistance Please
« Reply #26 on: July 06, 2005, 09:58:18 PM »
Thank you so much!
I should have read it over more carefully.
No biggie. I think my exam went ok...but I'm not sure either way. A lot of it felt pretty simple, but that usually means that I missed a co-efficient multiplier or something.

haha..Tim Hortons is a big conglomeration, as is Walmart.  We have 16 or 17 Tim Hortons on campus. It's crazy

Friends may not let friends go to Western, but atleast our library isn't sinking because we didn't calculate the weight including the books.

Q: How do you get a Waterloo grad off your front porch?

A: Pay him for the pizza.


Offline lemonoman

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Re:Enthalpy Assistance Please
« Reply #27 on: July 07, 2005, 02:11:23 AM »
Snap.

Offline lemonoman

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Re:Enthalpy Assistance Please
« Reply #28 on: July 07, 2005, 02:24:27 AM »
All of the UWO jokes revolve around how loose women are.

Definition (Slang)
============
Western -- v; to obtain commitment-free sex.
Usage : We're going out to the bar to see if we can Western tonight

Or,

Q: How many Western students does it to change a lightbulb?
A: One to change the lightbulb and four to find the perfect JCREW outfit to wear for the occasion.

Q. Why don't they have Christmas at Western?
A. They can't find a virgin and three wise men.

Good times.  ;D

arnyk

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Re:Enthalpy Assistance Please
« Reply #29 on: July 07, 2005, 09:18:24 AM »
Here's a zing on both of ya:

University of Waterloo:
Waterlosers. Being the top school in Canada, Waterloo students are smug and
arrogant believing that they are the best around! Damn you all for being right. Waterloosers have absolutely nothing to do all day but study. Well that and booze it up. The transit system sucks as does the night life. These guys come back to T.O. as often as possible to party it up. Oh yeh and they are even snobbier than Queens and St. George! This campus is ruled by Chinese peeps(in all things business) and by all those kids who you never really thought were THAT smart in school b/c they were so damn quiet. But if you're here for anything other than biomed, engineering and accounting you need to get over yourself! It's not THAT good a school! Trivia: the library was designed by Waterloo students and is currently sinking into the ground b/c they forgot to account for the weight of the books in the library. Way to go Waterlosers way to go!

University of Western Ontario:
It should just be called Western. It's not a university. It's Western. An anomaly. A night club/ resort that somehow got mislabelled as a university. Western doesn't count. Period. More so than the rest. At the other sucky universities you're really going to college. Here you're not even going to college, you're going to a non stop party. Your average intelligence is actually decreasing. Students here carry backpacks full of beer and those booze caps with the long straws attached. But hey there is justice in the world. A degree from Western is worth less than that 2 4 ! Side Note: If you're in business (post undergrad) the above doesn't apply to you at all.

Oh and the sinking library gag: That's a really common urban legend at many universities.  Just google it. ;)

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