Total Pressure of 2-Phase System: Dalton's Partial Pressure Law

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Discussion Overview

The discussion revolves around the application of Dalton's Partial Pressure Law to a two-phase system, specifically addressing the implications of including the pressure exerted by the liquid phase alongside the gas phase. Participants explore the validity of Dalton's law in this context and the treatment of hydrostatic pressure in calculations.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions the logic of Dalton's law in a two-phase system, suggesting that the pressure from the liquid phase should also be considered alongside the gas phase pressures.
  • Another participant asserts that Dalton's law specifically describes the behavior of gases, implying that it may not fully apply to systems involving liquids.
  • A participant provides a hypothetical scenario involving a closed container with liquid and gaseous components, raising the issue of whether hydrostatic pressure should be included in calculations of total pressure.
  • Another reply clarifies that hydrostatic pressure varies within the liquid, indicating that its inclusion depends on the specific pressure being calculated.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether Dalton's law can be applied to two-phase systems or how hydrostatic pressure should be treated in calculations. Multiple competing views remain on these issues.

Contextual Notes

The discussion highlights the complexity of pressure calculations in two-phase systems and the potential limitations of Dalton's law when applied outside of its typical context. Assumptions regarding the treatment of hydrostatic pressure and the definitions of total pressure are not fully resolved.

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Sum of Partial Pressures of Gas phase equals to total pressure of a 2 phase system? It sounds illogical because in a 2 phase system, the liquid phase also exerts pressure as well. Under dalton's partial pressure law, it states that the sum of total partial pressures of each gas component is equals to the total pressure of the gas.

y(i) Ptotal + y(j) Ptotal =Ptotal

If this law is applicable even to a 2 phase system, wouldn't it be inaccurate to not account for the pressure of the liquid phase also?
 
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Dalton's law describes behavior of gases.
 
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So as to state, if I have a closed container at 1 atm that has 2 component 2 phases of liquid air, liquid water and gaseous air, gaseous water, the partial pressure of gaseous water is then y(H20) x Ptotal whereby Ptotal = 1 atm. Since we are using Ptotal in the calculations, would we ignore the hydrostatic pressure caused by the liquid form as well?
 


Anyone please?
 


Hydrostatic pressure means that pressure on the bottom of the container differs from the pressure on the liquid surface. Whether you take it into account or not depends on what pressure you are calculating - it is not constant inside.
 

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