WHich is denser at the same temperature and pressure, dry air or air saturated wiht water vapor? Explain.?

Question

I think it's dry air but I don't know why...

Answer 1

Air saturated with H2O will have a lower density than dry air at the same conditions. This is because air is about 80 % Nitrogen. N2 has a mass of 28 g per mole and water H2O has a mass of 18 g per mole. So if water is taking up or traded for N2 the mass per volume will go down and the density will be lower.

This is related to Avogadro's law about the particles in equal volume of gasses, and Dalton's law of partial pressure.

Read more about it see :

http://en.wikipedia.org/wiki/Avogadro%27s_law

http://en.wikipedia.org/wiki/Dalton's_law

Answer 2

Roy g. Biv gave the correct answer and the correct reason.

Each of the gases contributes to the total pressure. The main gases are nitrogen, oxygen, and (in the saturated case) water vapor.

Of these three gases, water vapor is the lightest (i.e., it has the lowest molecular weight*).

Therefore, the humid air at the same temperature and pressure will be lighter.

The second response to your question is incorrect. Apparently this responder thought that the water vapor was included IN ADDITION to the same amount of air that was in the dry air. But if that were the case, the humid air would have a higher pressure (it's pressure would be the sum of the air's pressure plus the water vapor's pressure).

* IMPORTANT: YOU NEED TO KNOW HOW TO DETERMINE MOLECULAR WEIGHTS, AND HOW TO COMPARE THE MOLECULAR WEIGHTS OF NITROGEN, OXYGEN, AND WATER VAPOR.

Answer 3

Water vapor absorbs a number of the warm temperature, so in case you get rid of it the temperature would drop. i trust temperature would not change all that a lot, yet because the elements will be a lot dryer, you would not sense as warm. Take operating example residing in Arizona the position it really is dry and temperatures get over 100 tiers truthfully, and then residing in a South American us of a at sea aspect (like I used to), the position temperatures not often flow over 100 yet they sense like 100 and fifteen as a results of humidity.

Answer 4

Air with water vapor has more "parts per million" hence, more dence. It will weigh more.