come to me, the new column de ilkimiko Now a new book will be part of this area is called "chemical come to me" and is an example of how scientific discourse can be applied to things of every day . Thanks to the collaboration of my colleagues (Gabriel Valencia, the founder, Cataldo Valentini, Alessandro Ferrara and Doris "Crookes" Vinci), we conducted a debate arose spontaneously, a phenomenon of everyday life, trying to solve a doubt through the exchange of ideas.
This way of being fully represents the main purpose of this blog, or the dissemination and application of science to everyday life in a simple and explanatory.
course may also occur, as in this case, the nuances of speech takes a bit 'more technical, but the explanations, where demands are of course denied.
thank the guys who participated in the discussion and hope that this book will soon be enriched by new products, we carry the full transcript of the dialogue.
Chemical come to me ... Today I happened to open the freezer and leave as you all know (do not know what to call it) that strange breeze, a kind of cool mist ... What is the reason? (Explanation in thermodynamics)
Angelo : Technically it is called flash! It 'a phenomenon caused by sublimation (ie the direct conversion from solid to gas) of that substance odorless, colorless, tasteless, which consists of most of our ecosystem. ... The breeze is due to the flow of matter between two zones with different temperature. The flow of matter is "pushed" by the temperature difference.
Gabriel: Ok I thought I also the thermodynamics of irreversible systems to explain it .. what is wrong is not the sublimation (there is as well) but the fact that if the vapor sublimates must have at least 100 °, ie the system has absorbed energy from the environment ... the framework of the delta h of melting and evaporation over another certain amount .... seen that the environment has a temperature greater than 100 degrees (hopefully) the absorption of energy from the environment can only lead to ice melting and not to the sublimation ..
Angelo E 'where you're wrong. The temperature difference is large enough to provide the energy needed for sublimation, a high number of particles. Following the gaming tends to reach the state of the system in which ... is missing - the air of the kitchen - very fast.
In fact, the energy barriers are a relative concept. Let me explain: it is true that we need a certain amount of energy to be processing, but it is also true that there are fluctuations of energy around a mean value. In light of this, some particles, the number is highly dependent on the width of fluctuation may exceed a certain energy barrier as that of sublimation. Ovviemente tend to return immediately to the lowest energy state, or rather, in the most probable.
Gabriel: Ok I thought of that ... namely, that small particles according to the Boltzmann distribution able to leave the ice and go in the vapor phase. This means that the steam must have 100 degrees, empirically if I put my hand to 10 cm from the block Ice cools the hand. It 's a matter of fact, and not 100 °, but it is a cold vapor. The ice is temporarily condense the water particles of air (humidity in the neighborhood of the system (creating the breeze), but at the same time those affected by the temperature of the environment and spread as aerosols (as it appears moisture ), but with a lower temperature.
The experiment to test this would be to put the block of ice in an anhydrous and see if it comes out the breeze.
In practice the breeze is due perhaps to the temporary condensation of air humidity.
Angelo Who absorbs the energy released by the process of condensation of water particles dispersed in the air?
Remember that we are at the triple point, where the three states of aggregation coexist in the same space.
Gabriel: One moment the triple point dell'acqua è ben lontano... il vapore praticamente non è gas, ma l'umidità dell'aria che trovandosi su un intorno più freddo condensa (questo spiegherebbe il bianco in quanto la luce viene diffusa nella goccia) ma allo stesso tempo l'intorno superiore (l'aria) fa in modo di diffondere la condensa creatasi nell'ambiente come aereosol. (quando ti fai la doccia il vapore condensa sulle piastrelle perchè la piastrella ha una temperatura minore)
Angelo: E siamo d'accordo, ma la domanda era another (born a new debate). Who absorbs the energy released by the condensation of water particles?
imagine from where the whole process and find the answer. However, the explana ... it to your original question is correct.
Gabriel: is absorbed from the air, a gas tends to homogenize the kinetic energy of the particles, of course, to an average, then at the end of the room air (the air) will have a small delta temperature less. The problem is: how do to dimostarre if my assumption is correct?
The assumption is quite correct, the fog is a condensation (an aerosol) and water vapor, the temperature of the environment has yet It is as if you behave like a gas: released to the environment.
remaining in doubt and waiting for someone to do the experiment I have proposed, I propose a new question.
Alexander bequests reflect on one thing: if as you say, that it takes 100 ° C to vaporize the water, washed the floor with your mother Never dry!
As Angelo said, some particles have the energy to leave, and since the system is not closed they are not forced into equilibrium with the liquid, but only increase the entropy of the environment and within this scatter their energy (and then perhaps re-condense elsewhere, but you can not know)
after the liquid reaches another thermal energy (Example: the sun of the open window in the room where your mother has washed) and the question is being used by other particles (as you said hits the Boltzmann distribution) to escape and so on.
Same thing for the sublimation of water from the freezer (or freezer if you prefer)
you made one mistake, connect the concept of heat (energy needed to do ....) with the concept of temperature, heat and temperature are the same thing, then you will not find the particle at 100 ° C by placing a hand on the ice in the freezer.
Gabriel: How does a particle to sublimate if the environment is 25 °? admit that the ice around based, how many particles pass the barrier and go into the vapor phase at the instant when the round has just melted? certainly few and certainly the diffraction of light in the drop would be so small that it is not even visible to the naked eye (we would not see so much steam). The floor dries to the Boltzman distribution, but it is evaporating, that particles are in gas phase have 100 °, but they are always removed as a liquid aerosol. Ok, I myself, found good example! It's cold (3 ° is sufficient), there is fog. When you exhale the smoke out of your mouth. This is due to the fact that the air coming out from our much warmer than the air outside the lungs (which shall act for the block of ice) condenses almost immediately and see the smoke until the condensation does not spread. Certainly the air in our lungs is 100 ° and defective in liquid for that matter, and then Boltzman no longer valid. It 's just condensation.
Doriana: I would agreement with Valencia, the breeze that forms is due to the condensation of water vapor in the air (outdoors) around our system. If we open the freezer the cold air coming out of the latter will certainly at a temperature lower than the air surrounding (Say 25 ° C) and consequently tends, by the latter to buy back up to the heat balance and therefore the particles of vapor cools, condenses.
Angelo We understood, but the issue is still unresolved, what state are the particles at low temperature than air cooled ?
Solve this question.
Gabriel: Liquid course, but in a state of aerosols. The moisture is found incidentally in this state.
Cataldo: For me it is simply the condensation of water vapor in the air. The energy lost by these particles is clearly absorbed by the ice that tends to melt, for me it is. The dear and good old basic thermodynamics should not betray.
Alexander Unfortunately, although the phenomenon is apparently simple and common la termodinamica "basilare" non basta, il sistema (il freezer) è aperto, e la termodinamica basilare va bene solo per sistemi isolati o chiusi.
---:"per me è semplicemente la... condensazione del vapor acqueo in aria..."
quindi secondo te quella che vedo uscire dal freezer non è vaporizzazione del ghiaccio, ma la condensazione dell'aria esterna al freezer?
---:"l'energia persa da quelle particelle viene assorbita palesemente dal ghiaccio che tende a sciogliersi"
che l'energia termica debba andare dal corpo più caldo a quello più freddo siamo d'accordo, ma non credo che dobbiamo guardare solo l'umidità dell'aria(lo dico perchè hai fatto riferimento alla condensazione particulate air).
open the freezer you establish a current, due to different temperatures between the inside and the outside of the freezer, then the mass of ice is found to be immersed in the hot fluid (air) and that energy is sufficient heat to allow the passage state of particles of water vapor.
Gabriel: What you said that being an open system and thus an irreversible system, one must look at in another way. But the state diagram of water says that at 1 atm and 298k is allostato liquid. so how does a sublime with the environment? Ammesso che Boltzman per questo sistema non c'entra o comunque c'entra molto poco.
Alessandro: In effetti, mi sono andato a vedere anche io il digramma dell'acqua e una spiegazione non l'ho trovata, ma sono solo delle idee.
Per esempio mi è venuto in mente, che quella che vediamo uscire dal freezer , non sia acqua, ma l'anidride carbonica, disciolta nell'acqua al momento del congelamento, per quest'ultima sarebbe possibile sublimare a temperatura ambiente.
Però a questo punto vado nel campo delle ipotesi, e non mi azzardo a dire di più.
Anyway how do we know the truth? The need to find us, or someone goes on to inform the proper authorities?
Gabriel: This example was a possibility that I had not even remotely considered. If somebody did my experiment in anhydrous environment will solve the doubt. In any event I think since the carbon dioxide can sublimate the contrary view of the water and its concentration in the water to say the least negligible in any case I do not think that it can produce all that smoke. Oh the humidity of the air is not so abundant.
Cataldo: Trust mist that is due to the cooling of moist air due to ice. To get the sublimation should go to temperatures below 0 ° C and pressures of the order of tenths of a bar. In those temperatures are within a refrigerator but no one has the freezer working pressures bassisime.
Gabriel: I checked the state diagram of carbon dioxide ... impossible that there is CO2 in solid form, so no sublimation ...
guys are ... Every body has a soul .. so even the water .. and if it were the soul of the water that makes room for the soul of ice? no one has thought of?
Angelo As they say: Who Found! I caught a blurb, small, and in a very beautiful on phosphate water, I suggest you read, where it is explained, in short sublimation. In the article, I quote, there's a bit where it says that: "In reality, the best way to observe the sublimation is to not use water, but carbon dioxide, as shown in this image. Dioxide Dry ice is carbon frozen solid that sublimates at a temperature of -78.5 degrees centigrade. The fog you see in the picture is a mixture of carbon dioxide gas and cold air cold and damp, created by the sublimation of dry ice. "
read the whole article from this link: Water cycle
Ali
