Vapor Pressure in a Barometer (EK 1001 chem question)

[spyderracing32]

This is in regards to EK Chem 1001 #527. When you have a barometer and a fluid with a vapor pressure of 12 torr and you replace it with water (vapor pressure of 24 torr), I don't understand why the water level in the tube will fall. Since the vapor pressure is going to be the same throughout the fluid in the barometer, would it not exert its vapor pressure on the part of the solution exposed to the atmosphere equilibrating the vapor pressure over the fluid in the tube?

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[HawkeyePostOp]

Try making a diagram and label all the pressures the water in the column is exposed to.

It may also help to imagine this: If you think equilibration plays a role in the short run, imagine what would happen to the problem if you put started closing the seal and finally closed it. The level would still drop.

It doesn't matter that the other side is exposed to air, the water in the column is pulling down on itself, creating a semi-vacuum. A liquid with a higher partial pressure will release more gas into this vacuum and will cause the level to drop.