Accounting for Liquid Water Density in Ideal Gas Pressure Calculations

[dbag123]

Homework Statement

in a jar that has an airtight lid there is water. Temperature is raised to 120C, and as a result the pressure of the water vapor is 1,99bar. Calculate the partial pressure of dry air and the total pressure.

Relevant Equations

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First calculate the total pressure, but that gives me p2=p1*t2/t1 = 2,86 bar and partial pressure of 0,87 bar which is wrong. any tips?

 

[dbag123]

what about using the polytropic process to figure out the partial pressure of the dry air at 1 atm?, the increase would be 0.3375 bar and that is the right answer, initial temperature is 90C

 

[Chestermiller]

what about using the polytropic process to figure out the partial pressure of the dry air at 1 atm?, the increase would be 0.3375 bar and that is the right answer, initial temperature is 90C

Why do you need to use a polytropic process? This is an equilibrium problem.

What is the exact word-for-word statement of the problem?

 

[dbag123]

in a jar that has an airtight lid there is water. Temperature is raised to 120C, from 90C, where the pressure of water vapor is 0,7 bar and the air 1 atm and as a result the pressure of the water vapor is 1,99bar. Calculate the partial pressure of dry air and the total pressure.

 

[BvU]

Makes a difference ! What happens to the 1 atm when going from 90 to 120 C ?

 

[Chestermiller]

in a jar that has an airtight lid there is water. Temperature is raised to 120C, from 90C, where the pressure of water vapor is 0,7 bar and the air 1 atm and as a result the pressure of the water vapor is 1,99bar. Calculate the partial pressure of dry air and the total pressure.

You need to assume that the change in the volume of liquid water is negligible.

 

[jbriggs444]

You need to assume that the change in the volume of liquid water is negligible.

One could account for the density of the liquid water. However, since liquid water is approximately 1000 times as dense as steam at 2.0 bars, one might expect such an accounting to affect the result only in the third significant digit. The inputs here look to be good to only two digits at best.