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Frost, a change of state less obvious than others, which may appear magical in a certain sense and which, with its name, undoubtedly evokes frost. That "ice" that forms on the grass when it is so cold that the water vapor that "hovers" in the air does not remain vapor but turns into a myriad of ice needles. When they settle on grass or leaves, they form a sort of white "fluff", of fragile soft ice.
Frost exists in English but it doesn't have such a poetic name as in our language, the term is used "Solidification" or "reposition" or "desublimation". Maybe they give a better idea of what happens on a physical level but they have no charm at all.
It is defined by this term the transition from the gaseous state to the solid state of a substance when it occurs without going through the liquid state.
During this transformation, the number of particles does not change from start to finish, remains identical, the possibilities of movements that they can make vary. Moving from the gaseous to the solid state it is obvious that the particles they can no longer move freely in space, at the end of the change of state they are at best able to carry out small motions similar to vibrations. For this to happen, in the transition of state, the bonds that initially exist between the particles are all recreated
To avoid misunderstandings, it is better to clarify that the frost is often called sublimation, in everyday language, because it implies the passage through a condition of equilibrium, it depends on which texts, in the scientific field, we consult, to deepen this theme.
We talked about frost, initially, but there are more specific and appropriate examples to give an idea of what happens in frost. We can also do some pretty simple experiments with iodine pellets. Just get some and use a flame for heating, fitted with an inverted funnel and tongs. This is what it takes to observe the frosting of iodine and also sublimation.
With the flame the balls, solid therefore, if heated they become steam, as soon as everything is removed from the heating flame, you notice that the particles of iodine in the gaseous state return to the solid state creating crystals on the edges of the funnel. This happens without going through the liquid state and that is why we talk about frost.
In nature there is frost when the passage of water vapor occurs contained in the atmosphere solid state of ice, it is not obvious, it is necessary that the appropriate conditions of temperature and pressure are found.
Frosting and sublimation
As in the case of iodine, frost and sublimation are coupled since they are actually the opposite passage of the other. Sublimation is in fact the passage of a substance from the gaseous state to the solid state, also in this case the "intermediate" step does not take place, for the liquid state.
This phenomenon can be seen in those materials in which the molecules are weakly bound together and as soon as the temperature rises even slightly, they are able to separate and disperse. The most common materials, object of sublimation, I am the camphor and mothballs, present as moths, in balls, in many of our cabinets.
For frost to occur, it is necessary that there are boundaries temperature conditions but also pressure, ad hoc. Otherwise the change of status takes place in several stages "as scheduled". Temperature is therefore an important factor, to keep an eye on, to study this process, but it is not the only one.
During the change of state, however, after reaching the frost point, the temperature no longer decreases and the absence of thermal energy, which kept the bonds divided, allows the union of all bonds. And here we go from gas to solid.
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