Partial Pressure: Higher SP Determines P

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Discussion Overview

The discussion revolves around the concept of partial pressure in a vessel containing two substances in both liquid and gas states, particularly focusing on how the saturation pressure (SP) of each substance influences the total pressure in the system. The scope includes theoretical considerations and conceptual clarifications related to gas behavior and interactions.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes that the total pressure in the vessel will equal the saturation pressure of the substance with the higher SP.
  • Another participant challenges this idea, questioning the assumption that a higher saturation pressure would prevent the other gas from evaporating.
  • A third participant inquires if the pressure could exceed 15 B, suggesting a need for clarification on the pressure values.
  • One participant suggests that the gases will evaporate independently, leading to a total pressure that is the sum of the two partial pressures, while noting potential deviations due to interactions between the substances.
  • Another participant agrees with the independent evaporation idea but adds that if the liquids are mixed, boiling point elevation could affect the vapor pressures.
  • One participant expresses uncertainty and suggests that someone with a stronger chemistry background might provide better insights, while another clarifies that the discussion pertains more to physics than chemistry.

Areas of Agreement / Disagreement

Participants express differing views on how the saturation pressures of the substances interact and influence the total pressure, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Participants acknowledge that interactions between the two substances may lead to deviations from simple additive behavior, particularly in mixed states, but do not resolve the implications of these interactions on the overall pressure.

Yuri B.
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Am I assuming right the pressure in a vessel holding two substances (both being in the both liquid and gas states) will be equal to the saturation prerssure of the one which has the higher SP ? That is, for substance A whose SP at a given temp. is 10 B, for instance, and substance B whose SP is 15 B, the partial P will be 15 B?
 
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Why would you think that ? That would suggest that the gas with higher saturation pressure somehow prevents the other gas from evaporating, but that is hard to believe.
 
Do you mean it is over 15 B ?
 
My guess would be that the gases will evaporate almost independently, so both gases will have their respective pressure as if they were alone in the vessel. Then total pressure will be the sum of the two partial pressures. However, even approximately true, some deviation from simple sum should be expected, since the two substances influence each other, more in the liquid and at least a little bit in the gas...
 
Jano L. said:
My guess would be that the gases will evaporate almost independently, so both gases will have their respective pressure as if they were alone in the vessel. Then total pressure will be the sum of the two partial pressures.
Yes, those were my thoughts as well.

However, even approximately true, some deviation from simple sum should be expected, since the two substances influence each other, more in the liquid and at least a little bit in the gas...
Hmm, you bring up a good point. If the liquids are not mixed, I expect the total pressure should still be the sum of the two vapor pressures. But if the liquids are mixed, I guess you could get some boiling point elevation, which suggests a lowering of the vapor pressure at a given temperature.

Just an educated guess on my part after reading your post. Somebody with a stronger chemistry background may know better.
 
Redbelly98 said:
Somebody with a stronger chemistry background may know better.
It is not chemistry but rather physics.
 

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