Anonymous

Your question can be interpreted in different ways. For a given temperature and pressure, humid air is less dense than dry air.

Anonymous

"Assuming all doors, windows etc are totally shut" but that is not airtight, so the answer is NO.

Anonymous

Assuming no air escapes when the water vapour is added and that the temperature is unchanged (or rises) - yes. You have increased the number of particles bouncing around in the fixed volume; this is what gives the extra pressure.

Anonymous

Since you have a seal environment the addition of any vapor will raise the pressure. Of course if you added a couple of bricks it would also raise the pressure because the vapor space would be smaller. That is in effect what you do if you add water vapor.

Anonymous

Yes, the temperature would increase so the pressure would increase.