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Q & A: Water reaches boiling point but still add more heat?

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Most recent answer: 12/10/2014
Q:
When water reaches boiling point and your stove get's hotter does it still add more heat to the water?
- Sarah (age 13)
Moorestown
A:

When something boils, it is undergoing a phase transition to gas phase from liquid. While this happens, the material effectively is expanding drastically, i.e. the distance between the molecules increases. But molecules are not like inert spheres, there are forces between them. Just like when you separate two magnets from each other, you need to provide some external energy to overcome these forces. In the boiling case, this is done by your stove: it provides additional energy to your molecules, i.e. heat. Therefore as soon as you stop providing heat, the transition will halt, even though you may insulate the container perfectly so that the temperature is still at the boiling point. Nevertheless, assuming your city is at sea level and you have pure water, the temperature will be fixed around 100°C during the process, because the heat from your stove will be used mostly for this reaction.

Tunc


(published on 12/10/2014)

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