The simple, not demanding the proof truth – the volume of the liquid which is in an open vessel gradually changes. As just like that, disappears in anywhere nothing, a conclusion arises by itself - it evaporates. Process of transition of liquid to a vaporous state is called steam formation.
It is required to you
- - the closed flask with liquid;
- - heating device;
- - water;
- - air;
- - paper;
- - two vessels, wide and narrow.
Instruction
1. Steam formation can happen in two possible ways – evaporation and boiling. Molecules of liquid are in the continuous chaotic movement. Speed of some of them reaches value at which overcoming their mutual attraction is possible. Having appeared at a surface, such molecules leave liquid limits. At impacts some from remained, in turn, reach speed Process continues. Liquid gradually evaporates.
2. Conduct a simple experiment. Moisten one sheet of paper with water, and another air. It is easy to notice that air evaporates quicker. Therefore, steam formation process directly depends on a liquid sort, on its volatility. Substance which molecules have smaller force of an attraction evaporates quicker.
3. One more brief experience. Take two vessels – one wide, another narrow. Pour in them water. After a while you will notice that water evaporates from the first capacity quicker. I.e. the speed of transition of liquid to steam directly depends on the area of its surface.
4. Speed of process depends as well on liquid temperature. The it is higher, the more intensively there is a steam formation. It is easy to notice it. For example, the pools formed after a rain evaporate both in the summer, and fall. But in the first case it occurs much quicker.
5. At steam formation there can be also the return process. Some part of molecules comes back in liquid. If evaporation happens in the closed vessel, then at an initial stage the number of the molecules leaving liquid surpasses quantity of returning. Steam density gradually increases. The number of the molecules leaving liquid and returning to it to become equal. I.e. the quantity of molecules over liquid becomes invariable. There comes dynamic balance.
6. Steam which is in dynamic balance with liquid is called saturated. At this volume it is impossible to receive its bigger quantity. If process of evaporation continues, then steam is called nonsaturated. A conclusion arises by itself. Nonsaturated steam takes place at an initial stage of steam formation. Take the closed container with liquid, for example, a flask. Heat. At the initial stage of process of steam formation you will have nonsaturated steam.