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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Pookster on August 07, 2017, 02:55:33 PM

Title: Condensation problem
Post by: Pookster on August 07, 2017, 02:55:33 PM

Hello everybody,

I struggle a bit with a (maybe not so difficult problem). A closed container with a pressure of 200 000 Pa, a volume of 0.0130 m³ is filled with 1 mol of water vapor at a (calculated) temperature of 313 K. The surface tension of H2O is 69*10^-3 and the density is 1000 kg/m³.

Question: Will there be any condensation? And if so, what's the radius of the firstly formed water drops?

Answer: So, I think there will be condensation because it's a spontaneous process that results in a lowering of the Gibbs free energy. But I'm guessing there is a more precise (probably more numerical answer to this). Anybody any thoughts or a more elaborate explanation?

Thanks in advance.

Title: Re: Condensation problem
Post by: Borek on August 07, 2017, 04:32:38 PM

Not enough information to answer the question as worded.

You need to check the saturated vapor pressure for the temperature given.

Title: Re: Condensation problem
Post by: Pookster on August 09, 2017, 09:45:10 AM

That's also what I was thinking... Thanks anyways.

Title: Re: Condensation problem
Post by: Enthalpy on October 10, 2017, 07:31:43 AM

1 mol of gas at RT and 2bar occupies more or less 22L/2, so the vapour would indeed need that pressure to fit in the container.

Water at +40°C, less than +100°C, has an equilibrium vapour pressure under 1atm. Hence, condensation.

There is a minimum diameter that lets droplets grow faster than they evaporate. It depends on the temperature, pressure and surface tension. The initial droplets diameter might well be this minimum diameter. Should be available on Wiki or on the Web.