Why can we not say Water exist in 4 phases
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The word "aggregate" means a combination of different things. So by definition you are describing clouds as not a unique phase.
Good they are small droplets of water . why do the stay apart from each other , then beside they stay in groups . You can see them above clouds and you can feel the separation as you travel by air
( air pockets )
Thank you for the correction . But I will appreciate more if you come with a scientific comment .
exchemist
Valued Senior Member
Because they are condensing all the time from vapour. If you watch clouds for a while, you will see parts often disappear at the edges, while new parts appear elsewhere. This is because they occur where there is a rising stream of air, with enough water vapour in it reach the dew point and condense, once a sufficiently low temperature is reached (i.e. at sufficient altitude). So clouds are dynamic, not static, entities. The droplets initially formed do tend to coalesce, which is how we get raindrops. But there are also other factors at work. On a sunny day the clouds may evaporate, into less humid air surrounding them, at a rate that balances the rate at which they condense from the updraft responsible. If this occurs, they do not get the chance to coalesce into droplets heavy enough to start falling.
What more is there to discuss? You asked Janes for some further clarification of how clouds work, but that'only tangentially related to the original question.
Air pockets aren't a thing. They are a phenomena that happens when air moves unsmoothly, aka turbulence. http://www.foxnews.com/travel/2014/05/05/demystifying-flying-what-is-air-pocket/
Turbulence happens because air is differentially heated by exposure to sun and contact with warm land and seas while differentially cooled by exposure to space and contact with cold land and seas and because this differential heating volumes of air trade places, often messily. The Coriolis effect means these motions don't limit themselves to the vertical direction. So we get trade winds and chaotic phenomena like warm and cold fronts and areas of high and low pressure than the weathermen attempt to sort out for us. https://en.wikipedia.org/wiki/Turbulence
https://en.wikipedia.org/wiki/Coriolis_effect
https://en.wikipedia.org/wiki/Trade_winds
Finally, water has a certain temperature-and-pressure sensitive vapor pressure and vapor pressure is another way of expressing how much of water should be in the gas phase when at equilibrium. So clouds are portions of air where there is more water than equilibrium allows to exist as vapor. As exchemist says, clouds are transitory and the edges can be places of rapid formation or evaporation. As all physics is local, each droplet forms locally without knowledge that the cloud is big enough to be seen from the ground or space. https://en.wikipedia.org/wiki/Vapor_pressure
https://en.wikipedia.org/wiki/Cloud
Another phenomenon associated with phase change and local physics is critical opalescence. https://en.wikipedia.org/wiki/Critical_opalescence
Turbulence happens because air is differentially heated by exposure to sun and contact with warm land and seas while differentially cooled by exposure to space and contact with cold land and seas and because this differential heating volumes of air trade places, often messily. The Coriolis effect means these motions don't limit themselves to the vertical direction. So we get trade winds and chaotic phenomena like warm and cold fronts and areas of high and low pressure than the weathermen attempt to sort out for us. https://en.wikipedia.org/wiki/Turbulence
https://en.wikipedia.org/wiki/Coriolis_effect
https://en.wikipedia.org/wiki/Trade_winds
Finally, water has a certain temperature-and-pressure sensitive vapor pressure and vapor pressure is another way of expressing how much of water should be in the gas phase when at equilibrium. So clouds are portions of air where there is more water than equilibrium allows to exist as vapor. As exchemist says, clouds are transitory and the edges can be places of rapid formation or evaporation. As all physics is local, each droplet forms locally without knowledge that the cloud is big enough to be seen from the ground or space. https://en.wikipedia.org/wiki/Vapor_pressure
https://en.wikipedia.org/wiki/Cloud
Another phenomenon associated with phase change and local physics is critical opalescence. https://en.wikipedia.org/wiki/Critical_opalescence
DaveC426913
Valued Senior Member
I'm a little confused. You answered your own question.
So still only three phases.
http://classroom.synonym.com/explaining-condensation-exothermic-9621.html
So, what's the problem?
No, we cannot. Clouds are suspended water droplets - the liquid phase of water.
Correct. Clouds are an aggregate of liquid water droplets.
So still only three phases.
Actually, condensation is an exothermic process, meaning it releases energy.
http://classroom.synonym.com/explaining-condensation-exothermic-9621.html
So, what's the problem?
They are not.
Condensation is a phase change from a gas to a liquid.
Coalescence is the combining of particles of the same phase.
Incorrect. Clouds form without me lifting a finger.
Water molecules are not brought together, they merely exhibit a random statistical tendency to clump together (given ambient temperature and pressure). But just because they show this tendency, doesn't mean that all water molecules clump (even at 0° (C or F), the vapor pressure of water is above zero so some molecules don't clump) or that the locations of the clumps are ordered or otherwise known in advance.
No -- the water molecules need to give up energy to clump. Even water at 100°C needs additional energy to turn into gas. That energy, known to chemists as enthalpy of vaporization is 2257 kJ/kg , 539 kcal/kg. So the energy you need to turn 100°C water to 100°C steam is over 5 times what you need to turn the same mass of 0°C water into 100°C water.
The former is a term of art in thermodynamical descriptions of matter, the latter is a generic term having many meanings in different contexts.
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DaveC426913
Valued Senior Member
So, is the original question answered? You agree that there are 3 phases of water?
You are now asking about the formation of water droplets?
That's OK, I just wanted to know where we are.
You are now asking about the formation of water droplets?
That's OK, I just wanted to know where we are.
Or more.
But only three phases are both (meta)stable at natural temperatures and pressures found near the surface of the Earth and formed in time frames relevant to weather like clouds.http://www1.lsbu.ac.uk/water/water_phase_diagram.html
https://en.wikipedia.org/wiki/Ice
There is no easy path to ice IV or ice XII, but there are both ice $$\textrm{I}_c$$ and $$\textrm{I}_h$$. Additional research has resulted in Ice XVI, so seventeen forms of crystalline ice plus amorphous ice which is probably not thermodynamically stable at any temperature or pressure.
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Thank you I know what is a phase change , I know a vapor condenses it gives of heat in that step. Now i believe when you bring two or more particles together ( I mean particles a fine particle of water, not a molecule nor a dimer dimer of molecule , the particle might have billions of water molecules ) they in therm if density will be greater then the density of air and so they tend to fall to the earth surface. I hope this will make more clear what I mean by particle .
Now vapor to me is in a molecular form H2O not water
1 Water is transparent to light and refract light
2 Water molecules are transparent to light and probably refract less then liquid
3 clouds of water( the sake of argument ) are not transparent to light
4 molecules of water will condense and form particles of water , this small particles of water do not come down , because their density is lower the air density . Energy is needed to bring these particles together to coalesce in order to increase its density up to a point that particle density is greater then density of air.
My original question : what do we call the step. Particle density < air density, and the particles do not coalesce without external force
Water is MOSTLY transparent to light -- it has a (very!) slight blue color just like oxygen because it is literally absorbing some of the red. This is true for both $$\textrm{O}_2$$ and $$\textrm{H}_2\textrm{O}$$ in both liquid and gas phases at normal pressure. All transparent material refract light at their boundaries. That is to say, transparent materials have indices of refraction and those may vary by temperature and pressure and phase, etc. and all phenomena of refraction happens at the border between materials with different indices of refraction.
For high pressure, all bets are off as to color as the electrons which are involved in absorbing visible light get too crowded to work normally.
http://therovingapothecary.blogspot.jp/2012/11/chemical-of-week-solid-oxygen.html
The refractive index of water as a gas is less than the refractive index of water as liquid at the same temperature and pressure.
Because they consist of many droplets of liquid water and thus there are many curved surfaces where the index of refraction changes. In such material (clouds or writing paper or skin) the many curved surfaces means any initially collimated beam of light is scattered – nearby infintesimal rays take widely different journeys. Such materials have translucency. Thus clouds (like paper or the skin of the melanin-deficient) appears white when illuminated from the same side as the viewer, and light mostly gets through thin clouds (or paper) but thick paper is opaque to light because too much scattering happens and any tiny fraction that does get to the other side lacks any coherent image of the source of illumination on the distant side.
No, they have normal density about 800 times that of air. They do not fall quickly because they are physically small, and so weigh so little compared to the forces of Brownian motion that gravity doesn't have time to build up any substantial downward velocity. For tiny particles, the Brownian forces behind the phenomena of diffusion are not negligible compared to the forces of gravity responsible for the phenomena of falling and weight.
exchemist
Valued Senior Member
No, energy is not needed to make them coalesce. They do this naturally and this leads to raindrops. But the process takes time. A water droplet has the density of water, is thus heavier than the surrounding air, and will thus tend to fall. However the effect of its weight, for a tiny particle, is small compared to the effect of other dynamic processes. The particles may be dispersed by air currents, or evaporate again in air of lower humidity, before they have time either to fall or to coalesce. (Rpenner has also mentioned Brownian motion - another dynamic process that competes with falling and coalescence).
It seems to me that what you may be missing, in your approach to this issue, is a recognition of kinetic effects. You talk in terms of static properties, but it is the relative rates of the various processes that determines what happens.
I have in mind your post # 6 the dynamic process . forming particles and disappearing. There is also a build up ( larger cloud formation ) larger accumulation of particles , and that will reduce the space between the particle and they will coales . Then there is the case of inducing pressure on the particle system due to lightening , and on salting the clouds. During winter time we see the effect of reducing space between the particle and increase in clouds will increase pressure , we see snow. I assume this is the dynamic process you mean. But keeping in mind this does not go on on minute to minute . The clouds ( collection of particle ) stay on for days and longer . In the mean time before accumulation their entity are there , beside we have 3 layers of clouds ( particle accumulation ) not all of the produce liquid water that come to the earth.
Thank you for your input . What is your explanation that particles within the boundary "cloud " do not interact at non accumulate condition to produce rain .
I know you mentioned Brownian motion . I rather think the mainfree path between the particle is too large , and the collision will not be strong enough bring the surface close enough to interact and combine