A person has to deal with the process of boiling water daily. Hydrogen oxide is almost the most popular substance in our lives, but do we all know about its properties? What happens with the compound, which in the amount of eighty percent is part of the human body, at the time when the burning bubbles fill the cup and you are preparing everything for this ceremony in anticipation of a pleasant tea party.
Remembering the school physics course, we can easily give an explanation of how ice turns into liquid, and how steam appears. But not everyone can answer the difference between boiling and evaporation on the move. But the answer to this question lies on the surface. Its simplicity and even some kind of deep meaning make us once again pay tribute to the rationality of Nature.
Evaporation and condensation of a liquid occurs continuously and continuously. But now, when the temperature reaches a certain critical point, referred to in the literature as the boiling point of water, the process acquires a high intensity. During boiling, water molecules pass into a state of steam not only from the surface, but throughout the entire volume of the liquid. Visually, we observe how steam bubbles form inside the kettle and quickly rush up.
For each substance, this critical point corresponds to its own temperature at a certain pressure. A pressure of 100 kPa is considered normal conditions at sea level, the boiling point of water under these conditions reaches the classical indicators of 100 ° C. Having risen up to 4000 m, we go into conditions when the pressure drops and its value reaches 60 kPa. The boiling point of water in the mountains is lower than at its foot, and for the conditions indicated in the example, it reaches about 85 ° C.
Tourists, going on a long trip to the mountains, leave familiar teapots and pans below. They take special "pressure cookers" with them. The confined space provokes an increase in pressure due to excess steam pressure, as a result, the boiling point of water rises, and you can safely cook the usual products.
It affects its physical properties . The presence of impurities leads to a change in the boiling point. When a volatile substance dissolves in a liquid, the boiling point of water slides down, otherwise the water boils at a higher temperature.
There are many interesting and unusual properties of water, which we did not even know about. Experiments with boiled and ordinary water lead to interesting results. It sounds very paradoxical, but it remains a recognized fact that boiling water freezes faster than ordinary water. Water that previously succumbed to boiling also boils faster, not significantly, but the presence of sodium chloride in the water affects the boiling point (freezing).
Each of the above facts can be verified in an ordinary kitchen equipped with a gas stove and refrigerator. It is quite another matter to determine what the boiling point of water in a vacuum is equal to, experimentally. Indeed, theoretically, in a vacuum, water boils at room temperature.
But to conduct this experiment, you will need very simple equipment. We stock up on a regular disposable syringe and a piece of plasticine. Activities to prepare for the experiment will require simple manipulation of the needle. With a sharp, confident movement we break off its steel part, we plug the hole formed with plasticine. Fill a tenth of the volume into the syringe with water, remove the air and put the prepared needle on its “regular place”, the installation for experiments with vacuum is ready.
If you sharply pull the piston back, then part of the water will turn into steam with the intensity of full boiling, and this is in a room with an air temperature of about 20 ° C. By feeding the piston forward, we can observe how the steam turns into a liquid.
Using the example of the properties of water, we are once again convinced how much interesting and unusual the most ordinary natural phenomena can store.