Chemical Engineering in Daily Life - Question 5 - Standard Answers Available
Thread Content
This post was last edited by yjqin1 on 2015-8-20 at 18:23. When I was a child, our family would use a stove in winter. When the kettle on the stove is used to boil water, no abnormalities can be seen with the naked eye before and after the water boils; however, after turning off the heat, white steam appears above the kettle. Why is this?
White vapor consists of tiny water droplets formed when water vapor cools as it rises
The answer is correct, but a full score still cannot be given.
If you don’t turn off the heat after the water boils, will steam still appear?
It seems like the fire is too intense, heating up all the steam that is produced.
Is this condensed water? As the kettle cools down, water vapor turns into condensed water
As the temperature dropped, the steam condensed into water droplets, forming mist
The key point in this question, as mentioned by the original poster, is the appearance of visible white vapor after turning off the heat; the answer given on floor 6 is correct. The change in ambient temperature causes the water vapor to become aerosolized, resulting in the formation of white vapor.
White vapor consists of tiny water droplets formed when water vapor cools down as it rises. I agree with this view
Continuous heating occurs because the ambient temperature is high, so no \"white vapor\" is formed; once heating stops and the ambient temperature drops, it liquefies upon cooling.
Standard answer: Use it well with a coal stove, with a modern gas stove, or even with an electric stove. During the process of boiling water, the stove is definitely hot; hot air has lower density, so the air around the stove moves upward, to varying degrees. This is one of them. Secondly, when the water in the pot starts to boil, a large amount of water vapor is produced; this, of course, depends on the rate of evaporation of the water. Generally speaking, this process isn’t too slow. If you don’t believe it, see how long it takes to completely evaporate a pot of water A large amount of water vapor mixes with some of the relatively warm air around it. The generation of this large amount of water vapor causes the surrounding air to be stirred, mixed, and lifted; as a result, no area becomes supersaturated with water vapor, and therefore no mist appears. However, when you suddenly turn off the heat, the water vapor evaporates rapidly and loses its momentum (even if the stove still has residual heat, what is the specific heat of iron and stainless steel, and what are the specific heat and latent heat of vaporization of water?), and the rapid influx of air and its upward movement come to an end. At this point, the slowly rising water vapor meets the relatively cold air flowing in from the surroundings; as a result, the air cannot hold such a large amount of water vapor, leading to supersaturation and the formation of mist. Do this simple experiment: while the water is still boiling, try to feel the temperature at a height of half a foot above the kettle; the air there is transparent and scalding hot ； When you turn off the heat suddenly and notice mist at this half-foot height, try measuring the temperature here at that time. How much is the difference between the two?