Vapor pressure

[iDreamofDent]

Advertisement - Members don't see this ad

Hi guys

if you have a sealed container containing liquid and you add ONLY liquid then the vapor pressure should... increase, decrease, remain the same.

Kaplan says remain the same because VP only depends on temp and Pressure
but wouldn't increasing the amount of liquid in a sealed container increase the pressure?? so if you increase the pressure shouldn't the system favor the phase with the least moles of gas and therefore reduce the vapor pressure?😱

thanks

 

[solstice]

In majority of VP questions the container stays the same.
VP is the ability of molecule to break from the liquid phase and move to gas phase, it does so when the pressure is low and it has enough kinetic energy to do so (high Temp).

Now, when you add to the amount of liquid in the same container, your liquid surface area does not change, meaning that still the same number of molecules have access to the surface area to scape the liquid phase.

 

[americanpierg]

Hi guys

if you have a sealed container containing liquid and you add ONLY liquid then the vapor pressure should... increase, decrease, remain the same.

Kaplan says remain the same because VP only depends on temp and Pressure
but wouldn't increasing the amount of liquid in a sealed container increase the pressure?? so if you increase the pressure shouldn't the system favor the phase with the least moles of gas and therefore reduce the vapor pressure?😱

thanks

Pressure doesn't affect the vapor pressure to a degree that would matter on this exam. Increasing the pressure would increase the vapor pressure initially, but then that would cause condensation of that vapor pressure to increase until equilibrium is is reached again. Likewise, decreasing the pressure of the air inside the container will initially cause the vapor pressure to decrease, but that would cauase evaporation to increase to the point where the vapor pressure returns back to normal.

The only thing that affects vapor pressure is temperature, the molecular composition of the liquid/solid, and solutes within the liquid/solid.

 

[americanpierg]

In majority of VP questions the container stays the same.
VP is the ability of molecule to break from the liquid phase and move to gas phase, it does so when the pressure is low and it has enough kinetic energy to do so (high Temp).

Now, when you add to the amount of liquid in the same container, your liquid surface area does not change, meaning that still the same number of molecules have access to the surface area to scape the liquid phase.

Pressure wouldn't matter, because a liquid at a certain temperature will have the same kenetic energy. if the pressure is decreased, more molecules evaporates from the surface to even out the vapor pressure. if the pressure is increased, more molecules in the vapor condenses back into the liquid and the vapor pressure stays the same.

even if surface area is increased, more molecules may be able to leave the surface, but it also causes more molecules to condense back into the water, hence vapor pressure will once again stay the same

 

[iDreamofDent]

hey solstice and americanpie you guys really helped me out I guess I was looking at it from the perspective of what would initially happen rather than when it reaches the Eq