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Topic: This problem is about gas laws  (Read 2361 times)

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Offline uncreative

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This problem is about gas laws
« on: November 05, 2016, 07:30:58 PM »
Hello guys!
I'm posting again this problem with a better formatting and I'll show my attempts now. I didn't show my attempts because I was too lazy , but because I thought it was not necessary, and for this I'm really sorry!

The problem is the following

200 g of an organic compound with formula CaC2O4, 100 g of O2 and 50g of N2 are introduced inside a reactor with a constant volume of 100 L kept at 950 °C. The volume of the solid substances can be neglected, being smaller than the reactor volume. The following two reactions take place consecutively:

CaC2O4(s)-->CaO(s)+CO2(g)+CO(g)

2CO(g) +O2(g)-->2CO2(g)

Calculate the final pressure within the vessel.


Ok. So...what I thought was that to calculate the final pressure I have to calculate all partial pressure and then sum them up. So first I need to calculate the number of moles of each compound.
Firstly I calculate the ones I know the mass of, by dividing it by the molar mass. Once I find the number of moles of:

CaC2O4(s)
O2 and N2

I calculate the number of moles of the other compounds multiplying the values I found for CaC2O4(s) and for O2 by each stoichyometric coefficient.

For example number of moles of (2CO2(g)) is equal to: number of moles of (O2) times 2

actually I'm not sure about this.
 Anyway, after I found all the number of moles I use the formula: PV=nRT --> P=(nRT)/V

where n is the sum of all number of moles.


Thank you in advance and have a good day!


Offline Vidya

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Re: This problem is about gas laws
« Reply #1 on: November 06, 2016, 12:16:01 AM »
Did you check if any amount of O2 left unreacted or O2 is the limiting reagent or CO is the limiting reagent ?
Did you consider this?

Offline uncreative

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Re: This problem is about gas laws
« Reply #2 on: November 06, 2016, 01:56:25 AM »
I didn't consider this, actually. But how can I check it?

Offline uncreative

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Re: This problem is about gas laws
« Reply #3 on: November 06, 2016, 02:03:05 AM »
I have a question. The number of moles of CO(in the first reaction), must be equal to the number of moles of CO(in the second reaction)? Thanks

Offline Borek

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Re: This problem is about gas laws
« Reply #4 on: November 06, 2016, 03:21:03 AM »
I have a question. The number of moles of CO(in the first reaction), must be equal to the number of moles of CO(in the second reaction)? Thanks

All CO that was produced in the first reaction is available for the second reaction, but - as Vidya pointed out - you should check whether there is enough oxygen for all CO to react. You do that by finding the limiting reactant.
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Offline Vidya

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Re: This problem is about gas laws
« Reply #5 on: November 06, 2016, 06:02:19 AM »
I didn't consider this, actually. But how can I check it?
calculate the moles of CO formed in first reaction.
Now calculate the moles of O2 in 100g of O2 (review limiting reactant concept from any high school chemistry book).Look at the second balanced reaction and see how many moles of CO are required to completely react with the given number of moles of O2 in 100g oxygen gas sample. If O2 available is more and some amount is left even after the reaction then you need calculate the partial pressure of unreacted O2 also
P(Total) = P CO2 + PO2 (left unreacted)

Offline uncreative

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Re: This problem is about gas laws
« Reply #6 on: November 06, 2016, 06:43:45 AM »
Ok thank you very much. You have been really helpful, I understood how to do it, and I found the right solution.

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