Re: HOW DO U EVAPORATE AT REDUCED PRESSURE & TEMPERATURE?

As we increase the temperature of a liquid substance its particles move
faster and faster. In these conditions the probability of any of these
particles to get away from the bulk of the liquid and become part of the
gaseous phase will also increase. The higher the numnber in the gas phase,
the higher the pressure these particles can exert.[1]

The boiling point of a liquid corresponds to the temperature at which the
vapour pressure of the liquid equals that of the sorrounding environment.
At this point the particles can very easily go to become part of the gas
phase and lots of bubbles are produced.[2]

Thus if we decrease the external pressure the temperature at which the
boiling begins will be lower. This effect is easily recognised when we
travel to any place located at a sufficient altitude (tipically at the top
of a mountain higher than 3000 m).[3]

So if we are able to reduce the external pressure to a value lower than 0.5
atm the boiling point will reduce to about 50ºC.

Water bath
A water bath is used when we want to heat any substance without a direct
flame (specially when heating a flammable substance), make sure that the
heat is transmitted more uniformely and the temperature does never reach
any higher than 100ºC, the boiling point of the water.

So if we use a reduced pressure we will be able to make the substance boil
at a temperature lower than 100ºC, for which a water bath is more than enough.

References
[1] http://comp.uark.edu/~jgeabana/mol_dyn/KinThI.html
[2] http://www.chemguide.co.uk/physical/phaseeqia/phasediags.html
    http://encarta.msn.com/media_461541579/phase_diagram_for_water.html
[3] http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html