My dad says that cold water boils faster than hot. Is this true, and if so, why?
489650
No. Hot water will boil quicker because it is closer to water's boiling point. At sea level the bp of water is 100 C. (The boiling point is a little less at higher elevations). Once it gets heated to that it doesn't get hotter but rather it changes to a vapor. Cold water requires more energy over a longer period of time to heat it to the required temperature to reach its boiling point.
100455
Here's the thing: \nAdding salt to water actually increases the boiling point of water, so depending on how much salt you use, your boiling point of salt water could be something like 105 degrees celsius instead of 100.  Boiling point raising is an example of a colligative property, which is a property that is not dependent on what kind of particles you're using, just how many particles there are.  So if you added more salt, the water's boiling point would be higher.  \n\nThat means that your water would have to be at a higher temperature to boil.  This means that reasonably, it would take longer for you to get your water to that higher temperature, but not by a lot.  It would be roughly the same amount of time.  \n\nThe trick, though, is that because your water is boiling at a higher temperature, whatever you're cooking in that water is going to cook faster.  You're cooking it at 105 degrees instead of 100, so whatever you're cooking in the water will be done faster.  That's probably what your high school chemistry teacher meant.
216074
They don't!  The temperature of the water would actually take LONGER to drop than cold water would.  This is simple and very BASIC science!  Just like that stupid myth that cold water comes to a boil faster than hot.... damn, think for yourself and test it!
434026
If you place a glass of hot water in an ice box it will actually freeze faster than a glass of cold water. \n The reason is that the temperature difference makes the water circulate in the warm glass transfering the heat loss evenly through the contents, in cold water the outside freezes first which insulates the inside from heat transfer keeping the center liquid.\n Try it, you'll see.
67706
Yes. It takes more time for hot water to freeze - the cooling process takes longer when you start from a higher temperature.\n\nDifferent liquids freeze at different temperatures.\n\nIt depends how cold the place where you're putting the boiling water is, how much boiling water there is, etc.\n\nI think that each liquid has a specific temperature at which it freezes - it may not be associated with thickness.
662480
The one that heats up faster AND to higher temperatures is soil.\n\nWater can not gain or lose heat as quickly as soil due to latent heat. Water absorbs heat until it reaches the next phase change (vaporization) in which the water changes state.
131857
A liquid boils when its vapor pressure equals the pressure above the liquid.  At a given temperature, the vapor pressure of a liquid is constant.  At higher altitudes, the atmospheric pressure (the pressure above the liquid) is less than it is at lower altitudes, so water will boil at a lower temperature.
629453
warm water dissolves ice faster than warm air because it can transfer and absorb heat faster than warm air of the same temperature
621743
We cannot make a substance cold. \n\nWe can remove the heat from one place to another.\n\n  What is the difference between ice and water?\n\nFrom ice we have removed heat. The water is water because we have not removed heat from it. \n\nWe should not say ice is cold when compared to water, because we have not made it cold but we have removed heat from it.\n\nSimilarly when we want some hot coffee, we should ask, I want a coffee in which heat is added because we cannot make coffee hot.\n\nThank you.
432623
It depends on the temperature of the water and the air but if they are the same, then the ice in the water will melt faster because water is a better conductor for heat.
696743
NO! water will boil faster in the water in an area  above 6,000 feet. At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower, so it means it will boil faster.\n\nFor example: The boiling point of water is 100 °C (212 °F) at standard pressure. On top of Mount Everest the pressure is about 260 mbar (26 kPa) so the boiling point of water is 69 °C. It means lesser time to arrive to its boiling point.\n\nIf you were to boil water on Mount Everest,it  would be the lowest boiling point in the world because of its high elevation and low air pressure. If you were to boil water at the Dead Sea, it would reach the highest boiling point on Earth due to the low elevation and high air pressure. \n\nElevation affects the boiling point because of the amount of air pressure pushing down on the surface of the water. At a higher elevation the pressure is less and at a lower elevation  it is higher. When the pressure is higher, the molecules must absorb more energy in order to change state from liquid to gas therefore requiring more energy (temperature).♥
48257
ummm, no, water doesn't always boil at 100C.  It boils at 100c at one atmosphere, water will boil at room temperature in a vacuum.  But, hot water will boil faster, it requires less energy to heat the water, and the less water you have to boil the faster it will reach the boiling point.
1017824
Hot water will drop in temperature at a faster rate, but the cold water will freeze first except under certain circumstances in a phenomenon known as the Mpemba Effect\n\nhttp://math.ucr.edu/home/baez/physics/General/hot_water.html\nfor more details on the phenomenon
766842
1. microwaves heat water faster than boiling it over a heat source.\n\n2. microwaves have a more direct effect on an atom, since the energy is transferred directly form the MW to the atom, unlike the boiling water where it is transferred from heat source to water to the thing (w/ enzymes). the longer path means longer time.\n\n3. since the atoms (or molecules for enzymes) directly interact with the MWs, they are more likely to be destroyed than when boiling water is used. Hence the shorter time to ensure deactivation, and not destruction, is achieved
494092
As any sane and decent person would expect, hot water out of the tap will boil faster than cold water out of the tap. However, water that has been boiled once and allowed to cool will boil faster than hot water out of the tap. That's because boiling gets rid of the dissolved oxygen usually found in water, making it easier for the water to boil the second time around.
114884
Hot water does not freeze faster than cold, all conditions being the same, such as altitude, air pressure, and amount of cold applied to the water to make the water freeze.
335460
. Yes -- here is a general explanation for all you non-belivers.\n\nHot water can in fact freeze faster than cold water for a wide range of experimental conditions.  This phenomenon is extremely counter- intuitive, and surprising even to most scientists, but it is in fact real.  It has been seen and studied in numerous experiments.  While this phenomenon has been known for centuries, and was described by Aristotle, Bacon, and Descartes [1-3], it was not introduced to the modern scientific community until 1969, by a Tanzanian high school student named Mpemba.  Both the early scientific history of this effect, and the story of Mpemba's rediscovery of it, are interesting in their own right -- Mpemba's story in particular provides a dramatic parable against making snap judgements about what is impossible.  This is described separately below.\n\nThe phenomenon that hot water may freeze faster than cold is often called the Mpemba effect.  Because, no doubt, most readers are extremely skeptical at this point, we should begin by stating precisely what we mean by the Mpemba effect.  We start with two containers of water, which are identical in shape, and which hold identical amounts of water.  The only difference between the two is that the water in one is at a higher (uniform) temperature than the water in the other.  Now we cool both containers, using the exact same cooling process for each container.  Under some conditions the initially warmer water will freeze first.  If this occurs, we have seen the Mpemba effect.  Of course, the initially warmer water will not freeze before the initially cooler water for all initial conditions.  If the hot water starts at 99.9° C, and the cold water at 0.01° C, then clearly under those circumstances, the initially cooler water will freeze first.  However, under some conditions the initially warmer water will freeze first -- if that happens, you have seen the Mpemba effect.  But you will not see the Mpemba effect for just any initial temperatures, container shapes, or cooling conditions.\n\nThis seems impossible, right? Many sharp readers may have already come up with a common proof that the Mpemba effect is impossible.  The proof usually goes something like this.  Say that the initially cooler water starts at 30° C and takes 10 minutes to freeze, while the initially warmer water starts out at 70° C.  Now the initially warmer water has to spend some time cooling to get to get down to 30° C, and after that, it's going to take 10 more minutes to freeze.  So since the initially warmer water has to do everything that the initially cooler water has to do, plus a little more, it will take at least a little longer, right? What can be wrong with this proof?\n\nWhat's wrong with this proof is that it implicitly assumes that the water is characterized solely by a single number -- the average temperature.  But if other factors besides the average temperature are important, then when the initially warmer water has cooled to an average temperature of 30° C, it may look very different than the initially cooler water (at a uniform 30° C) did at the start.  Why? Because the water may have changed when it cooled down from a uniform 70° C to an average 30° C.  It could have less mass, less dissolved gas, or convection currents producing a non-uniform temperature distribution.  Or it could have changed the environment around the container in the refrigerator.  All four of these changes are conceivably important, and each will be considered separately below.  So the impossibility proof given above doesn't work.  And in fact the Mpemba effect has been observed in a number of controlled experiments [5,7-14]\n\nIt is still not known exactly why this happens.  A number of possible explanations for the effect have been proposed, but so far the experiments do not show clearly which, if any, of the proposed mechanisms is the most important one.  While you will often hear confident claims that X