Partial pressure vs mole fraction graph

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Discussion Overview

The discussion revolves around the relationship between partial pressure and mole fraction in a mixture, specifically addressing a claim from a textbook that the graph of partial pressure (P) versus mole fraction (χ) cannot pass through the origin. Participants explore the implications of a mole fraction of zero and its meaning in the context of the graph.

Discussion Character

  • Debate/contested
  • Homework-related
  • Conceptual clarification

Main Points Raised

  • One participant questions the validity of the textbook statement, arguing that if the mole fraction is zero, the partial pressure should also be zero, suggesting that the graph should pass through the origin.
  • Another participant expresses agreement with the initial claim, stating that the assertion in the book appears to be incorrect.
  • Some participants discuss the implications of a mole fraction of zero, with one noting that it indicates the absence of the constituent in the mixture, making the graph meaningless for that substance at that point.
  • There is a reiteration that a P, χ plot for a substance can only be meaningful for values where the substance is present, which raises questions about extending the relationship to zero mole fraction.
  • A later reply emphasizes the disagreement regarding the extension of the relationship p = Px to x = 0, highlighting that the absence of the species at that point complicates the interpretation of the graph.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the graph and the implications of a mole fraction of zero. There is no consensus on whether the graph should pass through the origin, and the discussion remains unresolved.

Contextual Notes

Participants highlight the limitations of the graph's applicability at zero mole fraction, indicating that the relationship may not hold in a meaningful way when the substance is absent.

mooncrater
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Homework Statement


There is a statement in a book :
" Graph of P vs ##\chi## is a straight line which ##cannot## pass through origin"

Homework Equations

The Attempt at a Solution


But if mole fraction of a component is zero then it can't form vapours because of which its partial pressure will be zero. So the P vs ##\chi## Graph ##should## pAss through origin. So is this given line wrong?
 
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It looks completely wrong to me.
 
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What would a molar fraction of 0 mean anyways? It means that there is no amount of the constituent present in the mixture. At molar fraction zero the graph does not describe the component anymore but anything that is not present in the mixture. And I guess that isn't really logical..
 
Molar fraction of zero means there is no substance present, that's perfectly logical to me.
 
Borek said:
Molar fraction of zero means there is no substance present, that's perfectly logical to me.

That is perfectly logical of course..
But imagine a P, xi plot for substance x in a mixture. At xi=0 the plot is not meaningful for describing substance x anymore cause substance x is not present anymore.
Simply put: a P, xi plot for a certain substance can only be plotted for values of xi where the substance is actually present.
 
T Damen said:
That is perfectly logical of course..
But imagine a P, xi plot for substance x in a mixture. At xi=0 the plot is not meaningful for describing substance x anymore cause substance x is not present anymore.
Simply put: a P, xi plot for a certain substance can only be plotted for values of xi where the substance is actually present.
What you are saying is that you object to extending the relationship p = Px down to x = 0, even though at x = 0, the species is not present so that its partial pressure p is equal to zero ( p = 0). And somehow this objection makes sense to you (because it doesn't make sense to me). I'm totally in agreement with Borek.

Chet
 

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