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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Bob7890 on January 26, 2012, 05:04:42 PM

Title: Mass to Moles to Molecules
Post by: Bob7890 on January 26, 2012, 05:04:42 PM

I need someone to show me how to do all of these equations correctly. I have not been able to figure it out at all. Or if you could link me to a website that explains all of this, it would be appreciated.

Finding how much is needed to react with X amount of chemical/g.
Like how much 02 is required to react with X substance completely.

Finding how much is needed between chemical X and chemical Y to produce chemical Z.
If the givens are in grams, moles, or in molecules.

Finding how many moles/grams/molecules are in X compound.

Limiting reactants.

I don't really have any example problems, as this isn't homework, just exam review, and I need help understanding it. An online resource would probably be better than one of you explaining this all tediously, so if you could link me, that would be great. Any specific questions from there, I'd redirect to here.

Thanks!
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Specific Question #1:
v2 = v1p1t2/p2t1

v2 = (10.0L)(101.3KPa)(83K) / (103KPa)(293K)

v2 = 239176

The problem I have here is that I get a big number as v2 at the end. Am I screwing up the equation process, or am I not reducing my units correctly?

Title: Re: Mass to Moles to Molecules
Post by: Arkcon on January 26, 2012, 08:51:46 PM

We get these sorts of problems often.  If you give us a specific textbook problem, we'll help you work through the steps, and you'll understand it.  Without a really problem to work with, its harder to explain.

Title: Re: Mass to Moles to Molecules
Post by: sjb on January 27, 2012, 02:46:35 AM

Quote from: Bob7890 on January 26, 2012, 05:04:42 PM

Specific Question #1:
v2 = v1p1t2/p2t1

v2 = (10.0L)(101.3KPa)(83K) / (103KPa)(293K)

v2 = 239176

The problem I have here is that I get a big number as v2 at the end. Am I screwing up the equation process, or am I not reducing my units correctly?

From this it looks like incomplete reduction of units. Eyeballing it, you can see that the two pressure terms nearly cancel, and that T1 is about three times T2, so your rough answer would be ~ a third of V13

Title: Re: Mass to Moles to Molecules
Post by: AWK on January 27, 2012, 04:42:24 AM

Quote

Specific Question #1:
v2 = v1p1t2/p2t1

v2 = (10.0L)(101.3KPa)(83K) / (103KPa)(293K)

v2 = 239176

Result is close to 3. You did a horrible error during calculations
Add additioal brackets to avoid mistakes.
v2 = ((10.0L)(101.3KPa)(83K)) / ((103KPa)(293K))

Title: Re: Mass to Moles to Molecules
Post by: Bob7890 on January 27, 2012, 07:10:33 AM

I think it was my calculator, lol.

Title: Re: Mass to Moles to Molecules
Post by: AWK on January 27, 2012, 09:05:14 AM

Calculator works according to your instructions.

Title: Re: Mass to Moles to Molecules
Post by: fledarmus on January 27, 2012, 09:08:33 AM

Quote from: AWK on January 27, 2012, 09:05:14 AM

Calculator works according to your instructions.

And when we can finally get computers to do what we want them to do instead of what we tell them to do, the world will be a good and happy place!