The phenomenon of boiling water, what is the phenomenon in water when water boils

From a microscopic point of view, the boiling process can be roughly divided into two stages: before boiling, the water in the beaker is heated, and due to the dissolved air in the water, small bubbles appear on the bottom and wall of the cup, and these small bubbles are formed by the separation of the air adsorbed by the inner wall and bottom of the cup. The small bubbles are surrounded by water, and the water is constantly evaporating into the bubbles.

The small bubble is small in size, and the air inside quickly reaches saturation, so there is not only air but also saturated water vapor in the bubble. When the water temperature continues to rise, the saturated vapor pressure in the small bubble gradually increases, so its volume also increases, under the action of buoyancy, the bubble rises from the bottom of the cup and the wall of the vessel, and at the same time, a small amount of air left on the bottom surface gradually forms a new bubble and rises. When the bubble rises to the upper layer of colder water, because the saturated vapor pressure in the bubble is less than the external pressure, the bubble gradually becomes smaller, so that the saturated vapor in the bubble gradually condenses into liquid, and finally only air and a small amount of water vapor escape from the liquid surface.

During the boiling process, as the temperature increases, the saturated vapor pressure in the bubble increases. When the temperature of the water rises to a certain extent, the saturated vapor pressure in the bubble increases to equal to the external pressure, and the whole water layer is at the same temperature, so the phenomenon of water vapor condensation and volume reduction will no longer occur in the bubble during the rising process. Due to the continuous heat absorption, the water around the bubble rapidly evaporates into the bubble, and the volume of the bubble continues to increase as it rises.

Finally, when the bubble rises to the surface of the water, it cracks, releasing a large amount of steam, and the water in the cup is churned up and down, forming a boiling phenomenon.

The latter topics have to rely on their own experiments, and it is useless to rely on imagination

You can't rely on imagination, it's better to do it yourself.

The boiling of water is a violent vaporization phenomenon; At this time, a large number of bubbles rise, become larger, and burst to the surface of the water, insideWater vaporemitted into the air. During the boiling process, although the water is continuously heated, it can only make the water constantly turn into water vapor, and its temperature remains the same.

Conditions for water boiling:

For a liquid to boil, two conditions must be met at the same time:

First, the temperature should reach the boiling point of the liquid.

Second, it needs to be heated constantly. The boiling point of different liquids is different, and the boiling point of water is at 1 standard atmosphere.

The next is 100; When water reaches its boiling point, it cannot boil if it cannot continue to absorb heat.

Details:The bubbles before boiling, the more they reach the liquid, the smaller they become. The reason is that when the liquid is heated, the temperature of the upper layer of the liquid is lower than that of the lower layer, and the solubility of the upper layer of the liquid is stronger than that of the lower layer.

In the bubble, some of the gases that cannot be dissolved in the liquid in the lower layer float to the lower temperature of the upper layer, and dissolve in the liquid again, making the bubble smaller. Most of the bubbles produced before boiling have become smaller and disappear before reaching the surface of the liquid.

The bubble during boiling is the vapor after the liquid has vaporized, and this bubble becomes larger the higher it reaches the upper layer of the liquid. This is because the bubbles in the lower layer are mixed with other bubbles as they float up, making the bubbles bigger and bigger. The bubbles produced during boiling will burst when they reach the surface of the liquid.

After rupture, it forms water vapor with the surrounding boiling water, and after leaving, it is cooled and liquefied into small water droplets, which is the "white gas" we see.

The above content reference: Encyclopedia - boiling.

Observed Phenomena:

1. Thermometer before boiling.

The number of indicators continues to rise and finally remains the same.

2. When boiling, bubbles bubble inside and on the surface of the water at the same time, and the bubbles become larger when they rise.

3. The sound of water before boiling is loud, and the sound of water becomes smaller after boiling.

4. Before boiling, only bubbles bubble at the bottom, and they become smaller and smaller during the rise.

Analysis] 1. Because the water temperature rises first, it continues to absorb heat after reaching the boiling point, but the temperature remains unchanged;

2. Since the depth of the bubble decreases during the rising process, according to P=PGH, it can be seen that the pressure of the bubble gradually decreases, so the bubble becomes larger when it rises.

This question is an experimental problem about "observing the boiling of water", and the characteristics of boiling should be mastered when solving the problem.

It can be analyzed from the noise size and temperature change before and after boiling; After reaching the boiling point in the water, it continues to absorb heat but the temperature remains the same.

In fact, not only water will boil, but many liquids will also boil, which is essentially the violent vaporization of liquid, which is a physical phenomenon, which is not only affected by temperature, but is determined by the pressure and temperature of the liquid itself.

We often say that water will boil when it reaches 100, because when water is heated to 100 at an atmospheric pressure on the surface of the earth, when it is heated to 100, it reaches the boiling point where it can boil, and then violent vaporization occurs. It is manifested by the fact that there will be a large number of bubbles inside and on the surface of the water, and these bubbles continue to gush upward, and the process of gushing out will be small and large, which leads to the continuous tumbling and surging of water, which is the boiling of water.

However, the boiling point is not fixed at 100, this is because in a state of atmospheric pressure, water will boil at 100, if it is less than an atmospheric pressure, then its boiling point will be reduced, for example, if you boil water on the Qinghai-Tibet Plateau, then the water will boil at about 90 degrees, this is because the altitude on the Qinghai-Tibet Plateau is too high, resulting in atmospheric pressure is not as large as the atmospheric pressure at sea level, so the boiling point of water is reduced. And if you fill an empty bottle of water with water at room temperature, and then keep pumping the air in the bottle, after a while, you will find that the water in the bottle at room temperature is boiling.

When the liquid boils, it will absorb heat, so the water will usually boil when it is heated, and if the heating is interrupted, then the boiling will stop, which is the relationship between boiling and heat. You may have seen such an experiment, after heating the water in a glass flask to make it boil, then the boiling of the water will stop, which is due to the interruption of the heat from the outside, the water has nowhere to absorb heat, and the boiling stops, and if you pour a little cold water on the surface of the flask at this time, you will find that the water inside actually boils again, which is due to the thermal expansion and contraction of the water vapor inside, and the sudden temperature decrease causes the air pressure in the flask to decrease. Then the boiling point of the water is lowered, and the water boils again.

Why do bubbles go from large to small before water boils, and from small to large when boiling?

The phenomena when water boils are as follows:

1. The boiling of the water is a violent vaporization phenomenon, and the boiling will produce a large number of bubbles, and the bubbles will rise slowly;

2. The bubble rises slowly, and with the change of time, the bubble will gradually become larger until it bursts on the water surface;

3. The bubble before boiling is smaller the more it reaches the top of the liquid, because when the liquid is heated, the temperature of the upper layer of the liquid is lower than that of the lower layer, and the solubility of the upper layer of the liquid is stronger than that of the lower layer;

4. When the bubble bursts, the water vapor in it is emitted into the air and becomes gaseous water molecules in the air;

5. In the boiling process, although the water is continuously heated, it can only make the water continuously turn into water vapor, and its temperature is kept unchanged.