Einstein once said Whether you can observe a thing or not depends on the theory which you use. It is the theory which decides what can be observed.
I just finished a unit with my Chemistry I students on the properties of matter, including phase diagrams. For one of the questions on their test, I did a demonstration in which I heated water to about 80°C and placed it under vacuum, causing it to boil. The test question was to explain what they observed in the context of the phase diagram for water, and to tell me what the pressure was inside the chamber at the instant when the water started to boil.
More than half of my students claimed that lowering the pressure added heat to the water, which elevated the temperature to 100°C.
Worst answer so far: When the pressure was reduced the water began to boil. It boiled because all of the oxygen was sucked out of the chamber creating more pressure inside. The more pressure there is, the less room for oxygen there is to cool down the water, creating more heat, thus boiling the water in the beaker.
