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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: nikita on October 13, 2008, 08:50:01 PM

Title: partial pressures and limiting reactant
Post by: nikita on October 13, 2008, 08:50:01 PM

Well, while i am working on my last question, i have one more.  this one says challenge question and obviously its a challenge to me, because its hard (to me).  Im jsut kind of upset because its worth 3 points and there are no hints to press on it.  its a lot of parts, and if they were all separate, i could do them, but i guess that is hence the "challenge."  i guess this time im just looking for what order i should do it in, in order to arrive at some answer.

The atmosphere slowly oxidizes hydrocarbons in a number of steps that eventually convert the hydrocarbon into carbon dioxide and water. The overall reactions of a number of such steps for methane gas is as follows:
 CH₄(g)+5O₂(g)+5NO(g) :rarrow: CO₂(g)+H₂O(g)+5NO₂(g) +2OH(g)
Suppose that an atmospheric chemist combines 150mL of methane at STP, 865mL   of oxygen at STP, and 55.5mL  of  at STP in a 2.2  flask. The reaction is allowed to stand for several weeks at 275 K.
If the reaction reaches 88.0% of completion (88.0% of the limiting reactant is consumed), what are the partial pressures of each of the reactants in the flask at 275 K
If the reaction reaches 88.0% of completion (88.0% of the limiting reactant is consumed), what are the partial pressures of each of the products in the flask at 275 K?
What is the total pressure in the flask?

first i need to find the limiting reactant?  actually, my head is spinning.  i dont know what to do second.

Title: Re: partial pressures and limiting reactant
Post by: nikita on October 13, 2008, 11:48:08 PM

well, i tried to think that theyre asking how much reactant are left after 88% is used.  I think CH4 is the limiting reactant, so i put .12 mol of each and used R and 275 divided by 2.2 L and come up with p= 1.23 atm for each.  i didnt put it in cause im still working on it.be

Title: Re: partial pressures and limiting reactant
Post by: Borek on October 14, 2008, 03:01:28 AM

Quote from: nikita on October 13, 2008, 08:50:01 PM

+2OH(g)

Something wrong here.

Finding limiting reagent is for sure first step.

Title: Re: partial pressures and limiting reactant
Post by: nikita on October 14, 2008, 01:16:45 PM

well, i never did get the answer.  they showed the answers to me and they were very small numbers and i still dont know how to get them.  i said the limiting reactant was CH4 as 1CH4 to 5O2 and 5NO to make 1CO2 and 1 H2O.  I tried with CH4 as the limiting reactant with 1 mol, 088 mol, .12 mol and they all came out wrong.  Obviously I have no clue what I am doing.  Even though I already got my grade, I would still like some help or just what I am doing wrong.  as for the 2OH(g), thats exactly how it looks in the problem, i didnt copy it wrong like last time and I add up all the H and O and it is equal. 

Title: Re: partial pressures and limiting reactant
Post by: nikita on October 14, 2008, 01:18:47 PM

ugh, never mind.  NO is the limiting reactant as I didnt use 22.4 again.  now i see why i got everything wrong.