Why can we not say Water exist in 4 phases

Discussion in 'Chemistry' started by timojin, Dec 16, 2015.

  1. rpenner Fully Wired Staff Member

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    Obviously, sometimes they do produce rain. In light of that, why is an explanation required? Current explanations have already listed other properties of clouds and that larger clouds (which have more total liquid water) scatter more light and thus the folk knowledge that dark (as seen from the side opposite the sun) clouds are rain-bearing clouds. Likewise, modeling them as systems where temperature and humidity disfavor evaporation leads to the conclusion that turbulent clouds and tall clouds are likely to produce chains of collisions of droplets resulting in larger droplet size and gravity dominating droplet diffusion.

    But lack of rain from thin clouds seems largely explainable from the context that between clouds and the ground is clear air where the temperature and humidity favor evaporation of any falling droplet. So it's not that droplets don't fall, but that they don't survive in any appreciable numbers to reach the ground.
     
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  3. timojin Valued Senior Member

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  5. timojin Valued Senior Member

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    O am su is a water molecule will have a lower density then water . If you are talking liquid and gas I might agree.
    Now. as you would look steam coming from a power plant you can see it and you could equate with a cloud , but the steam ( cloud ) fastly dissipated into transparency , but eventually at certain altitude a cloud is formed which have its own characteristic .
     
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  7. exchemist Valued Senior Member

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    Sorry this is too garbled for me to understand. Can you try again in clearer English?
     
  8. timojin Valued Senior Member

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    I meant in a reply " that air density is lower then water " I am not sure if this is true on molecular scale .
    As steam comes out from a power plant it comes visually as a cloud , but this steam cloud rapidly dissipates vapor ( which is not visible ). but these invisible gas as it enters at some altitude becomes a visible clouds So my point is . Clouds phase is different from liquid water phase . Question as an air plane immerses into a cloud does it get wet ? of not the cloud is not in a liquid phase.
     
  9. exchemist Valued Senior Member

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    OK thanks, much clearer now. A visible cloud, whether in the plume from a power station or a cloud in the sky, consists of liquid water in finely divided droplets. And yes a plane in cloud can get wet. Have you never climbed a mountain in cloud? It is quite damp, just as it is in a steamy bathroom. Or have you never been in a fog and looked at the vegetation around you? It is wet, isn't it? Fog is just cloud at ground level.

    So, no, there is no 4th phase. Water droplets are liquid water, but too finely divided to fall, just as smoke from a fire or a badly tuned engine is solid particles, but too finely divided to fall. The density of water is the same in cloud droplets as in a river, but, as has already been explained both by me and rpenner, there are other processes at work in clouds of droplets (or the fine particulate solids in smoke, come to that) that compete with the effect of gravity.
     
  10. rpenner Fully Wired Staff Member

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    Temperature (as you know it), pressure and density are not a property of individual molecules. They are properties of bulk matter.

    The definition of boiling temperature is when the equilibrium partial pressure of water vapor (the temperature-dependent saturation pressure) equals local atmospheric pressure.

    The ratio of densities of liquid water to air at normal sea level pressure and temperature is about 800:1.
    To good approximation water vapor and air obey the Ideal Gas Laws, so their densities at the same temperature and partial pressure are in the ratio of their average molecular weights which is between 18:29 and 5:8. But since the partial pressure of water is below atmospheric pressure if the temperature is below the boiling temperature the density of water vapor in air is even less than this.

    There is no "cloud phase" -- that's just a case of the vapor pressure of water being higher than the equilibrium dictated by pressure and temperature so some of the water becomes liquid particles (droplets) which scatter light. When the plume spreads out, their is more volume so even at cooler temperatures all the water can evaporate without the vapor pressure going above equilibrium and thus the visible plume vanishes.

    Yes it does. You don't need an airplane if you live in an area prone to fog which is just a cloud that touches the ground.
     
    Last edited: Dec 21, 2015
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  11. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    We can see clouds up close from land. We call that fog. Most people are aware that fog will form drips of water on suitable surfaces (damp fog); many trees rely on this for their moisture. Sequoia sempervirens comes to mind. https://en.wikipedia.org/wiki/Sequoia_sempervirens
     
  12. timojin Valued Senior Member

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    Following your thoughts, at higher elevation the vapor the vapor pressure is lower in the (clouds ) region, also as the altitude increase the temperature become lower . I can visualise a sort of equilibrium , fine , But there need an increase in cloud volume to increase a pressure within the frame of the cloud to bring the independent particles to coalesce to form a larger droplet until the gravity will bring the liquid down..
    By the way . fortunate me We had a fog in the area were I live . My observation was if you drive your front windshield gets wet but , the rear window was not wet. If you stand steel your windows do not get wet. That pits in my mind the question . I know the particles are water and they are somewhat independent of liquid state , until a force act upon them to convert them into a fluid state ?
     
  13. origin Trump is the best argument against a democracy. Valued Senior Member

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    Correct.
    Incorrect the clouds will not be at a higher pressure.
    Fog is already water in a liquid state. The tiny liquid droplets hit your windshield as you move and it gets wet.
     
  14. timojin Valued Senior Member

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    Perhaps I was misunderstood .. I mean within the cloud in the center of the cloud the pressure on the particle there will be a higher pressure as at the edges
    I understand we are talking of water and the water is liquid , but by been a particle it have its separate entity, otherwise it would be a continuous liquid water body, which is not
     
  15. origin Trump is the best argument against a democracy. Valued Senior Member

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    There won't be any pressure differences as far as I know.
     
  16. timojin Valued Senior Member

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    Then there should be no rain
     
  17. DaveC426913 Valued Senior Member

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    I think you are misunderstanding how clouds work and how raindrops form. It does not involve pressure gradients.
     
  18. rpenner Fully Wired Staff Member

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    That is a conclusion which does not follow from any antecedents. Thus it is a non sequitur and a clear demonstration that you are not meaningfully contributing to the marketplace of ideas.
     
  19. origin Trump is the best argument against a democracy. Valued Senior Member

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    You should look up how clouds form and why it rains. Just guessing is a waste of everyones time.
    Lets try this.
    When it is cold outside you can see your breath, right? The reason is simple. The air in your lungs is at 100% relative humidity at about 98.6 F. When you breath the air out into the cold air your breath cools and the cool air cannot hold that much water in vapor form so it condenses into a fog. If there is low humidity that day your breath will quickly evaporate, if the humidity is high then your condensed breath will persist for a while.

    Cumulus clouds form in the same way. Differential heating of the ground results in thermals. A thermal is a slightly warmer 'bubble' of air than the surrounding air and it rises. As it rises into the colder air aloft it will condense into water droplets when the relative humidity hits 100%. The size and persistence of the clouds will be dictated by several factors. If the humidity is not that high on the ground then the clouds that form will not be large. If the humidity is low at altitude the clouds will not be large. If the humidty is high in the lower levels and in the upper levels then the clouds may become large enough to produce rain that falls to the ground. The rain is produced when there is enough water droplets in the cloud that they come into physical contact and form larger and larger droplets until they fall as rain.

    This is a very abbreviated explanation. This information is easy to find and understand - google it and expand your mind.
     
  20. DaveC426913 Valued Senior Member

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    A key takeaway here, Timojin, is that vapour condensing to water droplets requires no pressure gradient, simply normal interaction of gaseous molecules. The molecules coalesce spontaneously into droplets as they cool - the mechanics are complicated, involving the di-polarity of water molecules, and the endothermic nature of condensation - but coalesce spontaneously they do.
     
  21. timojin Valued Senior Member

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    Thank you for you fancy insult. But to me people who use fancy words and insults are people who hide them behind their ignorance. If you can not explain in the most details is because you do not know and I could care less what degree you have.
     
  22. timojin Valued Senior Member

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    If your time is so important and you consider your selve very important you don't have to participate.

    If you care to explain: " if the humidity is high then your condensed breath will persist for a while." were will it go ?
    " If there is low humidity that day your breath will quickly evaporate, were will it go ?
    Let assume it will go up and be part of the clouds at about 2000 mtt were the temp. is about 20 C apparently will not condensate to form droplets of water , let continue the cloud rise to 4000 mt were the temp. is about 4 C why does not condensate and form droplets to rain ? what is your explanation
    How different is your statement from My # 29 , 31
    The rain is produced when there is enough water droplets in the cloud that they come into physical contact and form larger and larger droplets until they fall as rain.
     
  23. origin Trump is the best argument against a democracy. Valued Senior Member

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    The point is you can find this out in about 5 min with a quick Google.
    Like I said it evaporates. That means the molecules in the water droplets go into the gas phase and are dispersed into the atmosphere.
    Huh? Are you asking why your breath does not cause rain?
    The last sentence in post 29 makes no sense. Post 31 talks about differences in pressure between the center and the edge of a cloud, which is not accurate.
    Correct.
     

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