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Topic: Stoichiometry help  (Read 5357 times)

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Offline 0rion

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Stoichiometry help
« on: March 14, 2009, 07:07:05 PM »
Stoichiometry isnt usually a problem for me, but im having issues with this stupid wileyplus thing my course is 'pioneering' *slaps head*

Is this correct?

2C4H10(g) + 13O2(g) -> 8CO2(g) + 10H2O(g),,, because i got told it was wrong!!  >:(

And also, with a question like this
Pb(NO3)2 + Na2SO4  PbSO4 + NaNO3

if you are asked to balance it, and write the physical states...
is there a way you can work out what the states are, or do you just have to know the reaction?
I know one of the two will precipitate but ive never really been taught which one?
How would you approach this as a first year uni student?!  :-\

Offline 0rion

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Re: Stoichiometry help
« Reply #1 on: March 14, 2009, 08:08:58 PM »
Anyone??? 

lol


Offline Arkcon

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Re: Stoichiometry help
« Reply #2 on: March 14, 2009, 08:44:06 PM »
I don't see an error in the first one.  You may have to spend some time fiddling with wilyplus :(

You want to know the states.  And yes, it does seem a little daunting, trying to guess the states of matter for a reaction.  But think about it -- what states of matter do you know?  Which ones work for this reaction?  Solid lead nitrate, spread out in a nice thin layer in a pressure chamber, and vaporized sodium sulfate gas is pumped in?  For that matter, would you try to melt them, and have it happen in the liquid phase?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline cjtm92

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Re: Stoichiometry help
« Reply #3 on: March 14, 2009, 08:44:26 PM »
As for your first question, it is balanced correctly. I just had a test and the question was: Butane (C4H10) is ignited. And we were supposed to put the equation (balanced) and what kind of reaction it was plus the products. I put the same thing, and I got that one right... I'm holding it out in front of me now.

As for your second question-- you need to know the Solubility Rules (Google it, there is tons of info on it). When you do look it up, you'll find that NaNO3 will be a salt, if you were to do the reaction so it would definitely be soluble. But off of the Solubility Rules, Sodium and Nitrate are both soluble. You'd see that Phosphate is soluble, just like Nitrate, but lead is "low solubility (insoluble)". So, the Sodium Nitrate will be soluble, while the precipitate will be Lead III Phosphate.

Here's a great chart for those Solubility Rules: http://www.ausetute.com.au/solrules.html

Sorry my writing is terrible, I am about to leave, but I just had to answer you ;). Hopefully I made sense haha.

Offline 0rion

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Re: Stoichiometry help
« Reply #4 on: March 14, 2009, 11:33:29 PM »
Thanks for your help guys, that webpage was great btw :)

one more thing, could it be the physical states? i know butane is a natural gas, and im pretty sure that the product of combustion is water vapour, but do you think maybe the website wants me to specify water as a liquid?  :-\

Offline Borek

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Re: Stoichiometry help
« Reply #5 on: March 15, 2009, 04:43:49 AM »
one more thing, could it be the physical states? i know butane is a natural gas, and im pretty sure that the product of combustion is water vapour, but do you think maybe the website wants me to specify water as a liquid?  :-\

That would be my first reflex.

It is not clear what is the state of the water, as it depends on the conditions. At the reaction time it is a hot gas, but for some applications you will want it to be in the standard state - which for water is liqud.
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Offline 0rion

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Re: Stoichiometry help
« Reply #6 on: March 15, 2009, 07:36:40 AM »
Thanks everyone
that answer worked
although realistically it should be a gas, as combustion cannot occur below 100 degrees C anyway... :S

Offline Borek

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Re: Stoichiometry help
« Reply #7 on: March 15, 2009, 11:30:23 AM »
No reason why combustion won't occure below 100 deg C. Dpends on teh compound.

As for the liquid/gas and "realistically" - it all depends on how you define the reaction and its products. If I will burn some amount of butane in my room, produced water will be initially gaseous, but it will probably soon condense. I can't tell whether it is more "realistic" to assume produced water is gaseous or liquid, as it depends on the circumstances and time scale.
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