How Can You Calculate Vapor Pressure of Water at 43.0 C?

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Discussion Overview

The discussion revolves around calculating the vapor pressure of water at a temperature of 43.0°C, using the total pressure of the system provided as 758.3 torr. Participants explore the relationship between total pressure, vapor pressure, and the ideal gas law.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant seeks to calculate the vapor pressure using the equation Pwater = Ptotal - Pair, expressing uncertainty about the process.
  • Another participant questions the relevance of the ideal gas law, noting the change in state from liquid to gas at the given temperature.
  • A later post clarifies the full problem context, indicating the need to find the moles of air and subsequently the vapor pressure of water.
  • One participant suggests assuming the total pressure is 760 torr and proposes that the vapor pressure of water could be calculated as 1.7 torr, expressing doubt about this value being low.
  • Another participant comments on the nature of water as a liquid, suggesting that the low vapor pressure is not unusual due to the behavior of particles in different states.

Areas of Agreement / Disagreement

Participants express uncertainty about the calculations and the implications of the values derived. There is no consensus on the vapor pressure value or the appropriateness of the assumptions made.

Contextual Notes

Participants have not fully resolved the assumptions regarding the relationship between total pressure and vapor pressure, nor have they clarified the implications of using the ideal gas law in this context.

jKotha
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Ok, I need to calculate the vapor pressure of water.

All the information I am given is that the temp is 43.0 C, and I know the total pressure of the system is 758.3 torr.

Is there anyway I can calculate this using the Pwater = Ptotal - Pair equation? PLEASE HELP! Thanks guys

Jkotha
 
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Is it something related to the equation for ideal gas? but in pV = nRT, the "n" has changed cos in 43.0 C water is liq but vapor is gas. Sorry, I've got no idea about it since I'm doing biology...
 
first things first, state the full problem.
 
Full Problem

um.. that is the full problem. PV=NRT gives me the total pressure. I just need to find the vapor pressure of water.

This is what the problem says.
Consider the following data:
Temp = 43.0C Volume = 6.63ml
Barometric Pressure = 758.3 torr

a. Find the moles of air trapped in the cylinder

Ok, I can do this part by solving for n, in the ideal gas law. This is not a problem... the second part is the problem.

b. Calculate the vapor pressure of water, Pwater, at 43.0C


THIS IS THE FULL PROBLEM. Now I would really appreciate it if you can help. Thanks Guys..

jkotha
 
Assume that the total pressure is 760 torr and 758.3 as the partial pressure of the gas.
 
Thanks.. that might help

would that mean that the vapor pressure of the water would be 1.7 torr? That seems incredibly low. I'm assuming that total pressure = Pressure(gas) + pressure(water)

760 = 758.3 + Pwater

.. this doesn't seem right. That is really low.

hm... I don't know why this is so tough.

thanks

jkotha
 
It is not that unusual, water is a liquid and so the particles are not moving around as much as they are in its gaseous state of steam.
 

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