This demonstration uses liquid butane in a plastic bag to show evaporation and boiling under reduced pressure. As the butane evaporates, it absorbs heat, cooling the bag and causing condensation of water vapor on the outside.

1. Open a large zipper-lock plastic bag and place the nozzle of a butane spray can inside.
2. Seal the bag around the nozzle.
3. Spray butane into the bag for 3–5 seconds, then seal the bag fully. A small amount of liquid butane should collect inside.
4. Tilt the bag to allow the liquid butane to flow from one corner to another. Observe water vapor condensing on the outside of the bag.
5. Hold the corner of the bag containing the liquid and observe as it boils vigorously, inflating the bag.

Boiling Cold - FlinnScientific:

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• Compare how quickly condensation forms on the outside of the bag at different room humidities.
• Relate this to condensation on cold drinks or sweating pipes.

• Safety goggles, chemical-resistant gloves, and a chemical apron required.
• Butane is flammable - keep away from open flames and electrical sparks.
• Avoid direct skin contact with liquid butane, which can cause frostbite.
• Perform in a well-ventilated area.
• Dispose of butane gas safely by venting the bag in a fume hood or well-ventilated space.

• Why does liquid butane boil at room temperature when released into the bag? (Because reducing the pressure lowers its boiling point to below room temperature.)
• Why does water condense on the outside of the bag? (The butane absorbs heat as it evaporates, cooling the bag below the dew point of the surrounding air.)
• How does this experiment illustrate the cooling effect of evaporation? (Evaporation is endothermic, so it removes heat from the surroundings, making objects feel cold.)
• Where do we see similar effects in daily life? (Sweating, condensation on cold drinks, air conditioning systems.)