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From Wikipedia

Dry ice

200px|thumb| [[sublimation (chemistry)|Sublimation]] of dry ice when placed on the surface of water at room temperatureDry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide.

Dry ice is used as a cooling agent. Moreover, for some applications, the convenience of its sublimation "into thin air," in contrast to the melt-water left by warming water ice, may outweigh other costs.

Properties

Dry ice is the solid form of carbon dioxide (chemical formula: ), comprising two oxygenatoms bonded to a single carbon atom. It is colourless, odourless, non-flammable, and slightly acidic.

At temperatures above -56.4|C|F|1 and pressures below 5.13 atm (the triple point), changes from a solid to a gas with no intervening liquid form, through a process called sublimation. The opposite process is called deposition, where changes from the gas to solid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at -78.5|C|F|1.

The density of dry ice varies, but usually ranges between about 1.4 and 1.6 g/cm3 (87–100 lb/ft3). The low temperature and direct sublimation to a gas makes dry ice an effective coolant, since it is colder than water ice and leaves no residue as it changes state. Its enthalpy of sublimation is 571 kJ/kg (25.2 kJ/mol).

Dry ice is non-polar, with a dipole moment of zero, so attractive intermolecularvan der Waals forces operate. The composition results in low thermal and electrical conductivity.

History

It is generally accepted that dry ice was first observed in 1834 by French chemistCharles Thilorier, who published the first account of the substance. In his experiments, he noted that when opening the lid of a large cylinder containing liquid carbon dioxide, most of the liquid CO2 quickly evaporated. This left only solid dry ice in the container. In 1924, Thomas B. Slate applied for a U.S. patent to sell dry ice commercially. Subsequently, he became the first to make dry ice successful as an industry. In 1925, this solid form of CO2 was trademarked by the DryIce Corporation of America as "Dry ice", thus leading to its common name. That same year the DryIce Co. sold the substance commercially for the first time; marketing it for refrigerating purposes.

The alternative name "Cardice" is a registered trademark of Air Liquide UK Ltd. It is sometimes written as "card ice".

Manufacture

Dry ice is easily manufactured. There are common steps taken in producing dry ice. First, gases containing a high concentration of carbon dioxide are produced. Such gases can be a byproduct of some other process, such as producing ammonia from nitrogen and natural gas, or large-scale fermentation. Second, carbon dioxide-rich gas is pressurized and refrigerated until it changes into its liquid form. Next, the pressure is reduced. When this occurs some liquid carbon dioxide vaporizes, and this causes a rapid lowering of temperature of the remaining liquid carbon dioxide. As a result, the extreme cold causes the liquid to solidify into a snow-like consistency. Finally, the snow-like solid carbon dioxide is compressed into either small pellets or larger blocks of dry ice.

Dry ice is typically produced in two standard forms: blocks and cylindrical pellets. A standard block weighing approximately 30 kg is most common. These are commonly used in shipping, because they sublimate slowly due to a relatively small surface area. Pellets are around 1|cm|1|abbr=on in diameter and can be bagged easily. This form is suited to small scale use, for example at grocery stores and laboratories.

Applications

Commercial

The most common use of dry ice is to preserve food, using non-cyclic refrigeration.

It is frequently used to package items that need to remain cold or frozen, such as ice cream or biological samples, without the use of mechanical cooling.

Moreover, dry ice can be used to flash freeze food, laboratory biological samples, carbonate beverages, and make ice cream.

Dry ice can be used to arrest and prevent insect activity in closed containers of grains and grain products, as it displaces oxygen, but does not alter the taste or quality of such foods. For the same reason, it can prevent or retard food oils and fats from becoming rancid.

When dry ice is placed in water sublimation is accelerated, and low-sinking, dense clouds of smoke-like fog are created. This is used in fog mac


From Yahoo Answers

Question:Do you know the correct formula to solve this problem? Also is the same formula used to answer a similar question: How much energy is needed to increase the temperature of 35g of water from 0 degrees C to 20 deg C?

Answers:Two constants you need, and their units will tell you how to solve the problems. Specific heat of water 4.184 J/(g K) heat of fusion 334 J/g 1) 334 J/g x 35g = 11,690 J notice the g's cancel and we are left with J 2) 4.184 J/(g K) x 35g x 20C = 2,929 J again g's cancel, as do temperatures.

Question:First of all I KNOW that water and ice are the same thing, just for different temperature's. But then I saw the Nature channel, and in andartica ice turns right into air when people are going by? How come? What do you call it? "Don't breathe that spacific air, it was just ice." I need a better warning for my friends, we are going skiing in Colorado and I don't want them to inhail it.

Answers:Ice can turn to water wapour by sublimation (the direct change from solid state to gas state). But I think it cannot just turn into air...

Question:When I turn the hot water on in bathroom or kitchen it starts flowing (warm) then in a few seconds it slows dows and stops altogether. I have a cold water tank in the loft, a hot water one in the bedroom, and a central heating gas boiler in the kitchen. The pipework has been recently replaced by a friend. Cold water is fine. I don't understand how the two tanks and the boiler work together? The radiators work just fine, why doesn't the hot water work? We tried airing the tank by connecting the hot and cold water pipes in the kitchen and letting the pressure from the mains push whatever bubbles there were out through the system but we still have no hot water. With an eight weeks old baby in the house this is a disaster - please, help! I forgot to add that the pipes are copper (mostly new ones), and the taps in both kitchen and bathroom are all brand new.

Answers:My first thought would be a leak that only drips (releases pressure) when the pipes expand from the heat of the water. If you're using something other than copper, than I couldn't tell you. I would suggest calling out a plumber and making sure your friend didn't screw things up. BTW, the cold and hot lines have separate pipes, so even if the hot doesn't flow, the cold would.

Question:2 kg of water at 25 degrees C is added to a large quantity of ice at 0 degrees C resulting in ice-water. How much water is there in the final state? What is the total change in entropy in this process? Can anyone help me out?

Answers:let there be (m) kg of ice. it is mixed with 2kg water at 25C. >>> resulting stage is Ice-Water i.e water at 0C or water could just melt the entire ice. final temperature = 0C heat lost of water = heat gained by ice in melting -------- (1) 2 * 4181.3 *[25 - 0] = m [334.88*1000] m = 0.624 kg ========================= water available = 2 + 0.624 kg = 2.624 kg ==================== in equ(1) we have assumed that the ice-water mixing container is isolated from the rest of universe > that is when no heat escapes from the system, and is fully utilised in melting the given ice. thus its an adiabatic change, so change in entropy of the process (dS) = 0

From Youtube

how to boil water into ice :we used a computer chip processing machine to bring the atmospheric pressure down to around 1 torr to freeze the water. To answer some of your questions, this machine is as old as dirt and is only used in a classroom for demonstrations and how to detect leaks and so on... It did not cost 4 million dollars to freeze water. We did it after class "because we could". I would have put the original uncut video on but it took about 20 minutes to turn into ice. "kinda boring" bad enough to sit through 5 minutes. and no its not fake, anyone can do it with a strong enough vacuum pump. Hope this clears up any confusion.

A glass of water turns into ice fog :A glass of water is thrown into the air at -45F in Deadhorse, Alaska. Watch as liquid water instantly turns into ice fog!