Why Do Lakes Freeze on the Top First?
80416
Answer of vikram is correct, but, insted of the phrase `Ddensity increases' the phrase `density decreases' is suitable.As density of ice is less than that of water, it floates.Anomalous expansion of water is considered as the `boon of nature'. If the nature has not gifted this property to water, ice goes on settling in the bottom of the sea.Light and heat of the sun does not reach the bottom of the sea hence it does not melt. By this we can easily understand that no aquatic animal at the bottem of the sea can survive.
243894
Hydrogen bonding causes water to expand upon freezing.  The H-bonds cause the molecules to align into a structure that occupies more space than the liquid.  \n\nLiquid H2O does not do this because the kinetic energy of the water molecules constantly breaks any H-bonds that form.  As the kinetic energy (temperature) of the water decreases, the water becomes more dense, down to about 4 deg. C.  \n\nBelow 4 deg. C, the H-bond alignment of molecules outweighs the kinetic energy and the density of water begins decreasing.\n\nFrom Wikipedia:\nA simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold.
663824
it lowers the freezing point of water, make it more dense, so it has to e colder for water to freeze
435763
In order for snow to form the air must be supercooled. The process of snow formation starts w/ the Bergeron Process. This is also known as cold cloud precipitation.\n\nTiny ice particles form around condensation nuclei aka aerosols (pollen, dust, ash, salts, etc.) in the upper atmosphere.\n\nThey grow larger & larger until they can no longer be supported & gravity takes over.\n\nThe reason why the whole cloud won't freeze is b/c they are individual ice crystals. There is no way that they could stay suspended long enough to grow large enough to stick together.\n\nSo your answer is gravity takes over!
464226
Water mixes with water, rather than floating.  However, it is possible for warmer water to STRATIFY from colder - that is, the warmer water is on top while the colder is on the bottom.
323097
Ice has a lower density than water. When water freezes, the way in which the molecules rearrange to make a solid means that they are slightly further apart than in liquid water. Since density = mass/volume, and in ice there is slightly less mass in the same volume, ice is less dense.\n\nTherefore, because of Archimedes' buoyancy principle (the upward force on an object in liquid is equal to the mass of substance *displaced* by the object), ice floats. The ice displaces a volume of water equal to the volume of ice, but that volume of water has more mass than the same volume of ice, so the upward force is greater than the mass of ice. So the ice floats.
807739
They do freeze. They just don't normally freeze solid.\n\nIn the more extreme climates, like North Dakota, engineers incorporate heating systems into the tank design. Specifically, the central pipe that runs from ground level up into the bottom of the tank is called a riser. Water is pumped into the base of the riser and allowed to rise into the tank.  Many tank risers are wrapped with heat tape, covered with insulation and capped by an aluminum jacket.  In addition, a heating system may be installed in an adjacent building or into the valve pit underneath the riser.  The heater introduces heated water or steam into the base of the riser.  In either case, the heat rises into the tank to retard freezing.\n\nIce forms on the surface of the contents, in many cases several feet thick. Normally, this ice layer floats on the surface as the water level rises and falls.  Many times the ice freezes to the roof or upper walls of the tank and remains there as the level fluctuates underneath under daily usage.\n\nIn more temperate climates, steel ladders are installed inside the tank, and riser and water level control probes hang from the roof. In colder climates, all inside fixtures must be left out since the ice layer tends to rip them out.
149250
When the temperature of the water in the bottle approaches 32 degrees farehheit (the temperature where water freezes) is expands.  This pre-freeze expansion can rupture most nearly full containers.\n\nThe one good thing about this unusual physical phenomenon is that this is the reason that tce forms on the tops of lake or pond water.  This enables people to skate on the ponds in winter time.  The top layer of water freezes, while the lower water stays in a liquid form.
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Normally at 0ºC or 32ºF.  At that point water just begins to crystalize.\n\nThere are cases when water will not freeze, like \n- freezing point depression due to hydration,\n- freezing point depression due to osmotic effects (these are both equilibrium effects),\n- supercooling: the delay or absence of formation of an ice crystal in the absence of efficient ice nucleators and/or\n- the high viscosity\n\nFor every 0.5ºC (1ºF), water's viscosity will change by about 1.5%.\n\nWater viscosity is inversely related to temperature. The lower temperature, the higher viscosity.\n\nBut, water's dynamic viscosity at 0ºC is 3.732µ [ 10-5 (lb.s/ft2)] and the kinematic viscosity is 1.924v [10-5 (ft2/s)].
926439
fresh water freezes faster...ps, i gave you best answer on a question
694763
because ice is less dense than water, therefore it floats, this helps the species of the lake survive in winter time because the ice acts as an insulator
92209
It rains because the upper atmosphere is warmer than the air at the ground. Generally this is freezing rain, but not always.
628553
The wind would be blowing towards the north over the lake. This would push water on the surface of the lake towards the north. And you wouldn't even notice the difference in the level.
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It's because of the lower pressure with the higher altitude.  Remember the phase diagram denotes the phase of a particular compound in terms of the pressure and temperature.  If you're sufficiently talented with respect to the maths, refer to a physical chemistry text and research upon chemical equilibrium and dG/dn.\n\nhttp://www.freewebs.com/chemistryhomework\n\nEDIT:  \n\nYou said:\n------------\nThe phase diagram doesnot explain this.\nYou forgot that it takes higher pressure to shift the freezing point higher in the phase diagram, not lower pressure like up in the mountain.\n--------------\n\nIncreasing the pressure makes it easier to melt ice, e.g. the pressure exerted by ice skates result melted ice at the surface, this is a common excerpt in introductory chemistry texts.  Again, also consider dG/dP and chemical equilibrium.
172797
there is ice when it is cold, this is known as being frozen
873711
Not quite right.  It is most dense at 4 degrees C.  If it didn't, the water would freeze from the bottom up.  As it approaches 0 degrees, it becomes less dense and rises above the more dense warmer water and freezes on the surface and goes down.  Otherwise, fish would be on top of the ice and die after it froze.
35421
Ice will form on a surface that has water on it, if the surface is below freezing, or technically, can extract enough heat from the water to allow the water to fall to below freezing temperature.\n\nThis happens a lot when it has snowed, then there is a sunny or warm day, melting the snow to water because the ground temperature warms to above freezing.\n\nThen, at night, the ground will maintain the above freezing temperature for a while, but slowly cool off.\n\nA bridge has less 'mass' to maintain the warmer, higher, temperature, plus the air flowing above and below the bridge will cool the bridge faster, so it cools to below freezing faster. This causes bridges to frequently form ice more quickly than ground surfaces.\n\nUnder the right circumstances, the ice will form on the road as well. Just ask a busy auto body shop in winter.