Boiling is the process of changing the aggregate state of a substance. When we talk about water, we mean the change from liquid to vapor. It is important to note that boiling is not evaporation, which can occur even at room temperature. Also, do not confuse with boiling, which is the process of heating water to a certain temperature. Now that we understand the concepts, we can determine at what temperature water boils.
Process
The process of transforming the state of aggregation from liquid to gaseous is complex. And although people don't see it, there are 4 stages:
- In the first stage, small bubbles form at the bottom of the heated container. They can also be seen on the sides or on the surface of the water. They are formed due to the expansion of air bubbles,which are always found in the cracks of the container where the water is heated.
- At the second stage, the volume of the bubbles increases. All of them begin to rush to the surface, as there is saturated steam inside them, which is lighter than water. With an increase in the heating temperature, the pressure of the bubbles increases, and they are pushed to the surface due to the well-known Archimedes force. The characteristic bubbling sound can be heard as the bubbles continually expand and shrink.
- In the third stage, a large number of bubbles can be seen on the surface. This initially creates cloudiness in the water. This process is popularly called "boiling the white key", and it lasts a short period of time.
- At the fourth stage, the water boils intensely, large bursting bubbles appear on the surface, splashing is possible. Most often, splashes mean that the liquid has reached its maximum temperature. Steam will start to come out of the water.
It is known that water boils at a temperature of 100 degrees, which is possible only at the fourth stage.
Steam temperature
Steam is one of the states of water. When it enters the air, then, like other gases, it exerts a certain pressure on it. During vaporization, the temperature of steam and water remains constant until the entire liquid changes its state of aggregation. This phenomenon can be explained by the fact that when boiling, all the energy is spent on converting water into steam.
At the very beginning of boiling, a moistsaturated steam, which after the evaporation of all the liquid becomes dry. If its temperature begins to exceed the temperature of water, then such steam is superheated, and in terms of its characteristics it will be closer to gas.
Boiling s alt water
It's interesting to know at what temperature water with a high s alt content boils. It is known that it should be higher due to the content of Na+ and Cl- ions in the composition, which occupy an area between water molecules. This chemical composition of water with s alt differs from the usual fresh liquid.
The fact is that in s alt water there is a hydration reaction - the process of attaching water molecules to s alt ions. The bond between fresh water molecules is weaker than those formed during hydration, so it will take longer for a liquid to boil with dissolved s alt. As the temperature rises, the molecules in water containing s alt move faster, but there are fewer of them, which is why collisions between them occur less often. As a result, less steam is produced and its pressure is therefore lower than the steam head of fresh water. Therefore, more energy (temperature) is required for full vaporization. On average, to boil one liter of water containing 60 grams of s alt, it is necessary to raise the boiling point of water by 10% (that is, by 10 C).
Dependences of boiling on pressure
It is known that in the mountains, regardless of the chemical composition of water, the boiling point will be lower. This is due to the fact that the atmospheric pressure at altitudebelow. Normal pressure is considered to be 101.325 kPa. With it, the boiling point of water is 100 degrees Celsius. But if you climb a mountain, where the pressure is on average 40 kPa, then the water will boil there at 75.88 C. But this does not mean that cooking in the mountains will take almost half the time. For the heat treatment of products, a certain temperature is needed.
It is believed that at an altitude of 500 meters above sea level, water will boil at 98.3 C, and at an altitude of 3000 meters the boiling point will be 90 C.
Note that this law also works in the opposite direction. If a liquid is placed in a closed flask through which vapor cannot pass, then as the temperature rises and steam is formed, the pressure in this flask will increase, and boiling at elevated pressure will occur at a higher temperature. For example, at a pressure of 490.3 kPa, the boiling point of water will be 151 C.
Boiling distilled water
Distilled water is purified water without any impurities. It is often used for medical or technical purposes. Given that there are no impurities in such water, it is not used for cooking. It is interesting to note that distilled water boils faster than ordinary fresh water, but the boiling point remains the same - 100 degrees. However, the difference in boiling time will be minimal - just a fraction of a second.
In a teapot
Often people wonderat what temperature does the water boil in the kettle, since it is these devices that they use to boil the liquid. Taking into account the fact that the atmospheric pressure in the apartment is equal to the standard one, and the water used does not contain s alts and other impurities that should not be there, then the boiling point will also be standard - 100 degrees. But if the water contains s alt, then the boiling point, as we already know, will be higher.
Conclusion
Now you know at what temperature water boils, and how atmospheric pressure and liquid composition affect this process. There is nothing complicated in this, and children receive such information at school. The main thing to remember is that with a decrease in pressure, the boiling point of the liquid also decreases, and with its growth, it also increases.
On the Internet, you can find many different tables that indicate the dependence of the boiling point of a liquid on atmospheric pressure. They are available to everyone and are actively used by schoolchildren, students and even teachers at institutes.
