[LacunaMagala]

I am learning about pressure and collecting a gas over water. However, the teacher said something I don't understand.

When collecting a gas over water, and the water level inside is equal to the water, you can use the equation P_{total (or out)} = P_gas + P_H2O. However, she also mentioned that when the water level inside is higher than the water level outside, the atmospheric pressure is greater than the pressure inside.

So, how does this work? I can understand that it is such, but I am having trouble wrapping my head around it. If the volume stays the same, but the water level changes, how does the pressure change?

Thanks much!

[Enthalpy]

I'd say that the amount of gas differs between both cases.