Am I doing this vapour pressure problem correctly?

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SUMMARY

The discussion centers on calculating the remaining mass of liquid ethanol (C2H5OH) in a closed container at equilibrium, given its vapor pressure at 19°C is 40.0 torr. The ideal gas law (PV = nRT) is applied, using the gas constant R = 62.36 L⋅torr / mol⋅K. The calculation shows that 0.203 grams of ethanol vaporizes, leaving 0.797 grams of liquid ethanol in the container. The approach confirms that not all ethanol converts to vapor, aligning with the principles of vapor pressure equilibrium.

PREREQUISITES
  • Understanding of the ideal gas law (PV = nRT)
  • Knowledge of vapor pressure concepts
  • Familiarity with molar mass calculations (C2H5OH = 46.06844 g/mol)
  • Basic thermodynamics principles related to phase equilibrium
NEXT STEPS
  • Study the relationship between vapor pressure and temperature for different substances
  • Learn about phase diagrams and their implications in thermodynamics
  • Explore the concept of Raoult's Law and its applications in solutions
  • Investigate the effects of container volume on vapor-liquid equilibrium
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Chemistry students, educators, and professionals involved in thermodynamics and physical chemistry, particularly those focusing on phase equilibria and vapor pressure calculations.

Eclair_de_XII
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Homework Statement


'The vapour pressure of ethanol (C2H5OH) at 19°C is 40.0 torr. A 1.00-g sample of ethanol is placed in a 2.00 L container at 19°C. If the container is closed and the ethanol is allowed to reach equilibrium with its vapour, how many grams of liquid ethanol remain?'

Homework Equations


PV = nRT
R = 62.36 L⋅torr / mol⋅K

The Attempt at a Solution


Basically, when I tried to plug in all the numbers into the ideal gas equation (with the given mol number of 1/46), it wasn't quite equal. Then I figured, that not all the ethanol is converted into vapour; only some of it. And this equation really only applies to gases (a.k.a. vapours). I didn't know how much, so that's basically what I set out to find out with what I was given.

(40.0 torr)(2.00 L) = (x mol)(62.36 L⋅torr/1 mol⋅K)(292 K)
80 L⋅torr = x19209.12 L⋅torr
x = 0.0044 mol C2H5OH (g)
0.0044 mol(46.06844 g/1 mol) = 0.203 g C2H5OH (g)
1.00 - 0.203 = 0.797 g C2H5OH (l)
 
Last edited:
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Looks OK to me.
 
Thank you.
 

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