Cold boiling: bubbles without a hotplate

Lesson author: Яна Костова · EASYPhysics

Can water boil at room temperature? Lower the pressure in a virtual vessel and separate observations in the video from numerical model values.

Boiling must mean burning hot? Think again. Pavlo Viktor’s short video shows a flask, tap water and a vacuum pump. A student operates the pump and the teacher describes boiling at room temperature. The processed transcript gives no numerical pressure or thermometer reading; we do not invent them.

What explains the demonstration? A vapour bubble can grow within the liquid when saturated vapour pressure is sufficient to oppose the surrounding pressure. Lowering external pressure lowers the boiling temperature. About 100 °C applies to pure water near normal atmospheric pressure.

Predict first. Keep the water at 20 °C and lower pressure from 101.325 kPa to about 2.33 kPa. The model’s boiling threshold falls below 20 °C and vapour bubbles appear. Near 2.34 kPa, the threshold is approximately 20 °C. These are IAPWS-IF97 calculations, not measurements of the video apparatus.

Energy does not appear from nowhere. Making vapour requires energy. Sustained low-pressure boiling without heating would use the water’s internal energy and cool it, changing the conditions. This small model shows the threshold at the chosen pressure and temperature, not the full pump operation or time-dependent cooling.

Separate three phenomena. Evaporation occurs at the surface and can happen below boiling temperature. Boiling involves growing vapour bubbles within the liquid. Dissolved air escaping also creates bubbles, but bubbles alone do not prove boiling: the experimental conditions matter.

Test the return journey: increase pressure while keeping 20 °C. Will boiling continue? Explain using the new threshold. Then open the laboratory to compare pressure, heater power and heating time: they are different quantities.

This is a virtual experiment. Do not evacuate ordinary glassware at home. Vacuum equipment requires suitable apparatus and teacher supervision.

This is our educational interpretation for clear understanding and visual exploration. Original video: Pavlo Viktor, Cold boiling water. Thank you for questions that make learners want to test physics.

Test it in the virtual laboratory →