Wednesday, May 10, 2017

thermodynamics - Why does water stop boiling immediately after turning off the heat?



When I am heating water on a gas stove, it begins to boil after some time and bubbles of air can be seen escaping out.


However, as soon as I increase the amount of heat in the stove, the rate of escape of air bubbles increases immediately, and as soon as I turn off the stove, the air bubbles stop coming out right then.


In this case, I am boiling, water in a steel utensil. Steel is a good conductor of heat. Then why does this change take place so quickly with the change in heat?



Answer



In large part because under normal circumstances water doesn't get hotter than boiling - at that point it becomes steam, as you know. You can add heat and boil it away faster, but the water can only get so hot. When you remove the source of heat the water will quickly drop below this threshold. You're right on the knife edge of temperature.


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