Getting Empirical Forumula Using Ideal Gas Laws

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Discussion Overview

The discussion revolves around determining the empirical formula of a hydrocarbon (CxHy) burned in oxygen, based on the partial pressures of the resulting gases. Participants explore the application of the ideal gas law and the implications of limited information provided in the problem statement.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant notes the use of the ideal gas law (PV=nRT) but expresses uncertainty about the missing variables such as volume and temperature.
  • Another participant emphasizes that the problem lacks sufficient known conditions to proceed effectively.
  • A later post introduces a related problem involving the decomposition of acetone in a gas mixture, questioning how to determine the initial and final pressures of carbon monoxide (CO) given the changes in pressure.
  • Participants discuss the total pressure of the mixture and the partial pressure of water, suggesting that this information can help determine the molar ratio of water to carbon dioxide (CO2).
  • One participant mentions Dalton's law of partial pressures as a potential method to analyze the situation further.
  • There is a correction regarding the nature of the decomposition products, with a participant clarifying that it involves carbon monoxide and noting the importance of molar ratios.

Areas of Agreement / Disagreement

Participants express a general consensus that the problem lacks sufficient information to arrive at a definitive solution. Multiple competing views on how to approach the problem remain, particularly regarding the assumptions that can be made about temperature and volume.

Contextual Notes

Participants highlight limitations due to missing assumptions and the generality of the problem description, which affects their ability to apply the ideal gas law effectively.

Lancelot59
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Homework Statement


CxHy gets burned in oxygen gas and makes CO2 and water. Given the partial pressure of water and the total pressure of the resulting mixture I need to find the empirical formula.


Homework Equations


Well PV=nRT is the obvious choice...but all the information you see there is all that's given. The only other thing I was able to find was the pressure of the CO2 just doing some subtraction. The problem doesn't state a volume, temperature or anything else.

Can I assume that temperature is a constant and eliminate it? How about volume? I'm not sure about that, if I can then it might help.
 
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The problem description is far too general. You must have some known given conditions.
 
Nope that's it. All we know is that a hydrocarbon was burned, and the pressure of the products. We can't assume standard conditions because the pressure is off.

There's another problem I couldn't solve:

A mixture of the gases CO and CH3COCH3 (acetone) is trapped in a 1.0 L flask. The pressure in
the flask registers 100 mmHg initially but the pressure registers 114 mmHg after the acetone in the
flask is caused to decompose according to the following reaction at the same temperature:
CH3COCH3(g) H C2H4(g) + CO(g) + H2(g)
If all the substances present are in the gas phase, and CO is unchanged by any chemical reaction,
what were the inital and final pressures of CO, assuming complete reaction of the acetone?

Again, how can I proceed? I don't think enough is known.
 
Lancelot59 said:
Nope that's it. All we know is that a hydrocarbon was burned, and the pressure of the products.

Well you didn't include the pressure in your posting. :wink:
 
Oops...

The total pressure of the mixture is 1.2 atm and the pressure of the H2O is .686 atm. That still doesn't help much...does it?
 
Yes it does - it gives you partial pressure of CO2, and that means you know exact molar ratio of H2O and CO2.

--
methods
 
Actually it's just carbon monoxide. So that means everything in the decomposition is 1:1. I'll canker around with it and see where I can get. Dalton's pressure law seems a reasonable place to start.
 
Sorry, misread the question - but it doesn't matter much, it is still molar ratio that counts.

--
methods
 

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