What is the composition of the original gas mixture in mole percent?

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Discussion Overview

The discussion revolves around a physical chemistry problem involving a gas mixture of oxygen and hydrogen, where participants seek to determine the mole percent composition of the original mixture after a reaction has occurred and one gas has been removed.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents the problem and attempts to apply the ideal gas law, expressing confusion about how to proceed after setting up the equations.
  • Another participant suggests using a specific volume (22.4 liters) to simplify calculations, noting that the problem involves a ratio of gases removed.
  • A different participant argues that volume does not need to be specified since the volume remains constant, proposing to equate the initial and final states using the ideal gas law.
  • A later reply questions the meaning of 'n' in both the initial and final states, prompting further clarification on the variables involved.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of specifying volume in the calculations and the interpretation of the variable 'n', indicating that the discussion remains unresolved.

Contextual Notes

The discussion may be limited by assumptions regarding the ideal gas behavior and the specific conditions of the problem, which are not fully detailed in the posts.

Riles246
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Physical Chemistry Problem!

The total pressure of a mixture of oxygen and hydrogen is 1 atm. The mixture is ignited and the water is removed. The remaining gas is pure hydrogen and exerts a pressure of 0.4 atm when measured at the same values of T and V as the original mixture. What was the composition of the original mixture in mole percent?

I started by using the equation P=nRT/V. Since the V, R and T are the same before and after the reaction I solved the equation for P/n = RT/V so the two equations (for before and after the reaction) could be set equal to each other. Then I got stuck! Please Help!
 
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In this question you have a mixture of 2 gases at STP conditions. You remove all of one and some of the other in a ratio of 1:2. You are left with excess gas of only one component that has a certain pressure.

PV=nRT works if you know your volume. You will notice that you weren't given volume. You could use any volume and solve the problem but try using V=22.4 liters. It helps.
 


I don't need to use a volume since the problem states that the volume stays the same. I can set the initial and final states equal to each other by re-arranging the equation to RT/V=P/n. Then the P/n for the initial and final state of the mixtures should equal each other.
 


What do you think 'n' refers to in the initial state? In the final state?
 

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