Boiling water with ice

[ahhppull]

Homework Statement

I need to explain what happened here...

My teacher boiled water in a flask using a bunsen burner. Then he stoppered the flask and turned it upside down and boiled the water using ice.

Homework Equations

• Boyle’s Law is the principle that at a constant temperature the volume of a confined ideal gas varies inversely with its pressure.
• Boiling - A liquid boils at a temperature at which its vapor pressure is equal to the pressure of the gas above it. The lower the pressure of a gas above a liquid, the lower the temperature at which the liquid will boil.

The Attempt at a Solution

So I looked it up, and I don't quite understand it. Heres a website that explained it (http://www.Newton.dep.anl.gov/askasci/chem00/chem00894.htm). What I don't get is why the pressure dropped inside the flask?

 

[ahhppull]

My teacher also said we needed to know what rapid evaporation was. I looked it up online, but couldn't find any clear explanations on it, so if any of you guys know, please explain it =D

 

[Mark44]

The pressure dropped in the flask because the steam in the stoppered flask cooled. Turning the flask upside-down brought the steam into contact with the cooler part of the flask. As the steam cooled, water condensed from it leaving the remaining air in the flask at lower pressure. This enables the water to boil at a lower temperature.

That's my explanation...