why does it take so much more energy to boil 10 grams of water than to melt 10 grams of ice?
546552
It is called latent heat or the amount of heat required to change phases.  The latent heat of vaporization is usually much great than that of freezing.\n\nEach chemical or molecule has a different latent heat to change from liquid to gas.  It is also interesting that when water vapor condenses into liquid water, it gives off the exact same amount of energy that it took to boil it.\n\nNow think of dry ice (frozen carbon dioxide).  It goes straight from solid to gas (sublimation) and think about how much of a kick (freezing power) it has.
739180
Warm water is absorbed easier into the body.  Cold water takes longer to absorb, therefore burning more calories.
512779
Well... break it down to formulas. 1 calorie is the energy needed to heat 1 gram of water by 1 degree celcius.\n\nSo to heat 1000 grams of water (1 liter) by 1 degree, it takes 1000 calories. Now double the water to 2 liters and it will take 2000 calories.\n\nIf you are adding heat at a rate of 1000 calories per minute, then 1 liter of water heats at 1 degree celcius per minute and 2 liters heat at a rate of 1/2 degree celcius per minute. So yes. It is linear.\n\nHOWEVER (there is always a however) there are many factors that go into this in a lab setup. Namely, a larger volume of water will have more surface area and disipate heat to the suroundings faster. Also, a larger pan (wider) will heat faster than a taller pan. Etc, etc, etc.
638380
Heat will always travel from the warmer to the cooler. For example, an ice cube might be 32 degrees. If it is sitting in a room with an air temperature of 70 degrees, the heat in the air will travel into an ice cube until it melts completely. Once it melts, the water it was made of will continue to absorb the heat in the air until it is the same temperature as the air. The same occurs with oil in an engine, or any other object. Some things absorb or lose heat faster than others, and the more of a temperature difference there is, the faster the heat travels from the warmer object to the surrounding air, water, or whatever. An ice cube will melt much faster in boiling water than it will in cold water. Water will also freeze faster the colder the freezer is. I have proven this a number of times by putting room-temperature water bottles in various freezers. Some freeze in less than an hour, some freeze in several hours, depending on the freezer's temperature. Here's a conversion for Celsius and Fahrenheit.\n\nConvert Fahrenheit to Celsius F=1.8(C)+32\n\nConvert Celsius to Fahrenheit C=(F-32)/1.8 \n\nTo answer your other question, it has nothing to do with how many degrees per gallon of water in order to freeze it. What is important is that the air temperature is below freezing. The farther below freezing the air is, the faster the water will freeze. The more water there is, the longer it will take to freeze. The warmer the water is, the longer it will take to freeze. There are several variables. The volume of water, the temperature of the water, and the temperature of the air. It is the same for motor oil, or any other liquid. The rate of heat transfer is different for everything.
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
541181
See this answer.  Dig into the citations for the reference articles in them.  The second also has references.\n\nHot freezes faster in many cases, given certain controls such as same amount of water, same size and shape container, standard pressure etc.  There  is at least one experiment showing that water at 90 degrees C will freeze quicker than water at 18 degrees C.  This is significant since one side is quite close to boiling and the other is basically room temperature.\n\nIf you are not a high school student, I would look up linear programming ( a branch of algebra not computer science) and develop a sensitivity analysis to determine the impact of various effects.
143592
Heat required to rise the temperature of  ice from \n-10 degree centigrade to 0 degree centigrade \n= ms(t2-t1)\n=10 * 2.1 * 10  g* {joule/(g*degree)} (degree)\n=210 joule\n\nHeat required to convert ice to water  \n=mass x specific latent heat fusion of ice \n=10 * 336  g*joules per gram\n=3360 joule\n\nHeat required to rise the temperature of  water from \n0 degree centigrade to 100 degree centigrade\n=ms(t2-t1)\n=10 * 4.2 * 100\n=4200 joule\n\nHeat required to convert water to steam\nmass x specific latent heat of vaporisation of water\n10 * 2264\n22640 joule\n \nHeat required to rise the temperature of steam from \n100 degree centigrade to 110 degree centigrade \n= ms(t2-t1)\n=10 * 2 *  (110-100)\n=200 joule.\n\ntotal of all is  30610 joule.
601632
Water boiling has to do with air pressure.\n\nThe higher your elevation, the less pressure exerted on the water, so it can boil at a lower temperature.\n\nThe closer to sea level you get, the more air pressure there is, so it requires more energy to boil.  (Going lower then sea level will still increase the boiling temperature).\n\nIt's also important to note, that when water is boiling, it keeps a constant temperature.  So if you look at this graph of time vs average temperature....\n\n|.........../..\n|........../..\n|....------.... <---  Boiling Temperature\n|../...........\n|./............\n\nYou see that when the boiling occurs, the temperature does not increase.  Only when all the water is evaporated does the temperature increase.  This ALSO works for ice in water.  The water will remain at 0 degrees celcius till all the ice is melted.\n\nHope this helps you understand melting/boiling points.
971810
If the water is already frozen and you remove more heat, all you will get is colder ice.  Otherwise, we need to know at what point is it at in the latent heat of fusion.
220158
Do not offer bribes, this is immoral.\nMany here come to assist as a service.\n\nYour answer is here:\n\nWhen ice melts, kinetic energy of H2O molecules is increased by absorption of heat energy from the surroundings.\n\nHowever as the kinetic energy is increased to make the molecules move freely, Hydrogen Bonding among the water molecules becomes more effective and so a particular intermolecular distance is maintained among the molecules. \n\nThis is effective upto 4C.\n\nAfter 4C the H-bonding becomes so week as against kinetic energy that free movement of molecules is no more restricted and thus abnormal behaviour of water molecules is stopped.
482741
You need a few different constants to figure this out.\n\nWater has a Specific Heat of 1 kcal/kg/°C\nThat means it needs 1 kcal per kilogram to heat the water 1 degree celsius\n\nIt has a density of 1000 kg/m3\n\nIt has a Latent heat of Fusion of 80 kcal/kg (melting) and 65 J/kg (freezing)\n\nSo if you know the volume you can work out the weight of the water. Once you have the weight (or you already know it), you can work out the rate of the drop (or increase) of water temperature.\n\nOnce you get to the point of freezing, or melting, simply add on the latent heat, and you can then get the total amount of energy required to change the water from one temperature to the next.\n\nSo for example;\n\n1) How much energy to heat 2 kg water from 18°C to 100°C is =>\n\n2kg * 1 * (100-18) = 164 kcal (The heat up curve is fairly straight)\n------------------------------->\n\n2) 2kg of water from 5°C to -10°C is as follows;\n\n(2 x 1 * (5 - -10)) + (65 * 2) = 160 kcal\n\nCurve drops down fairly constantly, then flats out until the water turns to ice, then continues to drop until you are at your temperature.\n\nI hope that helps a little.\n\nIf you want to figure out the times for all this to happen, you need to either know what heat source you are using (for example the wattage of the kettle element), and also you need to figure out the heat losses from the container (e.g. kettle or pipe, etc.)\n\nThese can all then be converted to an equivalent kcal number.
408269
It actually can be, believe it or not.  It has to do with hydrogen bonds.  Water exhibits very strong hydrogen bonding due to its polarity, and in order to freeze, these hydrogen bonds in liquid water must be broken.  In hot water, more of these bonds are already broken, so a quick drop in temperature could allow the water to freeze before the hydrogen bonds reform.\n\nNote that this is strictly a kinetic or time-based effect.  Thermodynamics dictates that cold water will freeze faster since a smaller energy drop is required, but in some cases it is entropically favored for hot water to freeze faster.\n\nAlso note that stirring the water vigorously will also break hyrdogen bonds, so stirred cold water will almost always freeze before stirred hot water.  You will only observe the phenomenon of interest when the water is fairly pure and undisturbed, and the temperature drop is rapid enough.\n\nWe discussed this very problem in my graduate-level thermodynamics class.
787766
There is no set speed because ice melts from the outside first. A solid block of ice, 1000g, will melt more slowly than 1000g of ice cubes, which will melt slower than 1000g of crushed ice. The more surface area exposed, the faster it melts. Also, it depends on the temperature of the ice. Ice from a -5C freezer will melt faster then ice from a -30C freezer.\n\nYou have asked this question twice. Why don't you carry out an experiment and find it our for yourself, using a kitchen scale, a timer, and a thermometer?
862439
The steam.  It would have to go through a phase change and give up a bunch of energy to turn back into water at 100.  Assuming you mean equal mass of water and steam. \n\nSame question for ice.  How much energy does it take to melt 1 Kg of ice at 0 to water at 0?
62870
Cold Water. - Most of the time. \nI have tried and tested this before (Tap Water). The hot water normaly takes about 10 minutes longer. When using Tempratures like 30 degrees and 70 degrees this will begin to vary and warm water might start freezing faster than cold water. \n\nWarm water can in fact sometimes freeze faster than Cold water but it very much depends on the conditions.\n\nWhat you are thinking of is the Mpemba effect. This could be due to a number of factors including but not limited to Evaporation (less water needed to be freezed), Dissolved Gasses and Convection.\n\nFor a lengthy but thorough explanation see the link below.\n(Very reliable references) \nhttp://math.ucr.edu/home/baez/physics/General/hot_water.html
241754
Thermal intertia.  It works the other way too, cold water boils quicker than hot water.  The reason is when hot water is placed into the ice cube tray it immediately begins cooling.  Then when you put it into the freezer it continues to accelerate more and more quickly to the low temp desired.  Cold water would begin warming as soon as it gets put into the tray and then you have to cool it back down (opposite direction heating takes more energy)
1096429
Ice requires a crystalline lattice structure. The salt ions (Na+ and Cl-) physically interfere with the formation of that lattice structure by standing in the way of water molecules. A lower temperature is therefore necessary to form ice and so water that contains ionic salt can drop to lower temperatures before forming ice. The same general effect applies to boiling water. Because the salt prevents molecules from escaping into the atmosphere as gas, the boiling point is raised.\n\nNote: I assume you meant 0 degrees Celsius. The Fahrenheit scale is somewhat different, since water freezes at 32 degrees Fahrenheit. But don't let these numbers cause you to believe something different is going on in the salt/water/ice mixture. The Celsius scale is set such that water freezes at 0 degrees (absent salt). This doesn't mean that at 0 Celsius and below there is no temperature or energy. Just the same, below 0 degrees Fahrenheit compounds still have energy and temperature. Scientists tend to use another scale which more accurately depicts true temperature, which is the Kelvin scale. In the Kelvin scale, absolute zero- the temperature at which all molecules and atoms stop moving- is really 0. But 0 Kelvin is much lower than either 0 Celsius or 0 Fahrenheit. To convert from Celsius to Kelvin, just add 273 degrees (or subtract 273 from Kelvin to Celsius). So 0 Celsius is actually 273 degrees Kelvin.  \n\nIn any case, if you were looking for an answer that has to do with the chemical properties of the salt/ice/water mixture, and why, for example, salt tends to lower the freezing point (or raises the boiling point), my first answer is right.  Any solute you add to a solvent will change the colligative properties of the solvent.  It interferes with the organization of water molecules such that they have a harder time aligning into a crystalline ice pattern, and therefore a lower temperature is required for ice to form. Note also that whenever you have an ice/water mixture, the entire mixture maintains the same temperature until all of the water has turned to ice. That is, in pure water that contains ice, the water will stay at 0 degrees Celsius until all the water has turned to ice, and then the ice will gradually drop in temperature. The salt just lowers that freezing point, but the same applies, just that the salt/water/ice mixture remains at that lower freezing point until all water as frozen, then it drops further in temperature.