Does a confined liquid boil?

1. Aug 31, 2010

busyenergy

I would have thought no, but my textbook appears to imply that the liquid being boiled in a confined space doesn't at its normal boiling temperature but does boil at a higher temperature.

The reason I don't think a confined liquid can boil is because the external pressure in a confined liquid is replaced by the container. My book says that boiling initiates when the vapor pressure of the liquid is greater then the external pressure on the surface of the liquid. If the external pressure is the container only, then boiling can never happen unless the container were to break.

Even if the the external pressure was not only the container but also the pressure of the surface of the liquid on the vapor within the liquid (vapor boils from the bottom of the liquid upwards, right), the boiling point should be lower then if boiling were to take place in an open environment without a container because there is no atmospheric pressure within a closed container.

Really confused.

2. Sep 1, 2010

alxm

There's no atmospheric pressure within a closed container? Where did you close it, in a vacuum?

3. Sep 1, 2010

iratern

What about the pressure caused by gas phase of the liquid in the container?

(Also, unless in a vacuum there is going to be atmospheric pressure caused by the gases trapped in the container.)

Anyways liquid-gas transition (i.e evaporating) is not the same as boiling. Any liquid can evaporate at pretty much any temperature, it's an equilibrium though (You should know what an equilibrium is). Boiling is only the state that has the maximum evaporation rate.

4. Sep 3, 2010

lightarrow

Just to add a little bit of information.
Certainly the vapour/gas pressure inside a closed container could be much greater than atmospheric pressure (note that I said "could"). But, whatever the pressure, a substance cannot exist in the liquid state at temperatures greater than its critical temperature.
E.g.: water cannot exist in the liquid state at temperatures greater than 374°C, even if the external pressure were 100 atmospheres.