Question on water vapour and pressures

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Discussion Overview

The discussion revolves around a homework problem involving the calculation of the mass of water condensed from moist air when compressed isothermally. The context includes concepts of relative humidity, saturated water vapor pressure, and the ideal gas law.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on how to start solving the problem, expressing difficulty in finding the mass of water condensed.
  • Another participant asks for the pressure of saturated water vapor at 25 degrees Celsius, indicating a need for specific data to proceed.
  • A participant confirms using a chart to find the saturated vapor pressures at 25 degrees Celsius and then applies the ideal gas law to calculate the mass of water, incorporating relative humidity to determine the mass of water condensed.
  • There is a clarification that reading the pressure of saturated water vapor from a chart is necessary for the calculations.

Areas of Agreement / Disagreement

Participants generally agree on the need to reference a chart for saturated vapor pressures, but there is no consensus on the approach to finding the mass of water condensed, as some express confusion while others provide a method.

Contextual Notes

Participants rely on external charts for saturated vapor pressures, indicating a dependence on specific data not provided in the problem statement. The discussion does not resolve the initial participant's confusion regarding the calculations.

math_04
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Homework Statement



20 litres of moist air at 25 degrees celsius with a relative humidity of 75% are compressed isothermally to a volume of 4 litres. Calculate the mass of water condensed? (One method, find the original water vapour pressure, it will be increased by what factor?)

Homework Equations



pV= mRT

water vapour pressure = density x R x T

The Attempt at a Solution



Where should I start with this problem. Finding the mass is really hard here, the mass of water condensed is only part a of the question. if i had that, i could figure it all out. any hints in the right direction?
 
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What is pressure of saturated water vapour at 25 deg C?
 
sorry borek u lost me. am i supposed to read the pressure of saturated water vapour at 25 degrees off a chart? Because right now, I cannot see an equation that help me find the mass with the current information provided.
 
yea think i got it. I used the chart to search for saturated vapour pressures at 25 deg C, then used PV= mRT to calculate the mass of water. Then use relative humidity to find mass of water condensed.

cheers anyway
 
math_04 said:
am i supposed to read the pressure of saturated water vapour at 25 degrees off a chart?

Yes.
 

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