Updated April 27, 2018 By Chris Deziel
Water responds like any other compound to changing temperatures, but an anomaly occurs in a narrow range around the melting point, and it's a change that makes a big difference. When you heat ice, the molecules gain kinetic energy, and the ice expands until it melts. But once all the ice has turned to water and the temperature starts rising again, expansion stops. Between 32 and 40 degrees Fahrenheit (0 and 4 degrees Celsius), the melted water actually contracts as the temperature rises. Beyond 40 F (4 C), it starts to expand again. This phenomenon makes ice less dense than the water around it, which is the reason why ice floats.
Ice expands at a fixed rate, liquid water expands at an accelerating rate with increasing temperature and steam again expands at a fixed rate. Between the temperatures of 32 F (0 C) to 40 F (4 C), liquid water actually contracts with increasing temperature.
As a solid, ice can only expand linearly, which means the length and width of an ice cube can change. The coefficient of linear expansion for ice, which measures fractional change of length and width per degree Kelvin, is a constant 50 x 10-6÷ K. This means that ice expands in a uniform amount with each degree of heat you add to it.
When ice becomes liquid water, it no longer has fixed linear dimensions, but it has volume. Scientists use a different thermal coefficient -- the coefficient of volume expansion -- to measure the response of liquid water to temperature. This coefficient, which measures fractional changes in volume per degree Kelvin, is not fixed. It increases with mounting temperature until the water starts boiling. In other words, liquid water expands at an increasing rate as the temperature goes up.
When water turns into steam, it expands according to the ideal gas law: PV = nRT. If the pressure (P) and number of moles of vapor (n) maintain at a constant, the volume of steam (V) increases linearly with temperature (T). In this equation R is a constant called the ideal gas constant.
At its melting point, water exhibits a characteristic shared by no other compound. Instead of continuing to expand in the liquid state, it contracts, and its density increases until it achieves a maximum at 40 F (4 C). From the melting point to this critical point, the coefficient of expansion is negative, and at the point of maximum density, the coefficient of expansion is 0. If the temperature continues to rise, the coefficient of expansion again becomes positive.
If you reverse the temperature gradient and cool water to the freezing point, it starts expanding at 40 F (4 C) and continues to expand until it freezes. This is the reason water pipes burst in freezing weather and why you should never put a glass bottle full of water in the freezer.
QUESTION #371 Asked by: Remi Short Answer: by about 9% to 10% Long Answer: Normally, things expand when heated and contract when cooled. Water is an exception to this rule. Even though water does expand when heated and contract when cooled at most temperatures, water expands when cooled and contracts when heated between 4 degrees Celsius and 0 degrees Celsius. A very good web site about the properties and oddities of water can be found on the Okanagan University, Dept. of Geology website at: http://www.geog.ouc.bc.ca/physgeog/contents/8a.html Answered by: Charles Hill, Network Engineer, Deltona, FL Answer Hint: When water freezes, formation of ice takes place. It changes from liquid to solid state. Water crystallizes into hexagonal structure. It begins to take a more stable and definite shape. Complete step by step answer: The normal behavior observed in any substance is that they usually expand when heated as their density decreases and contracts on cooling as their density is maximum. But water is an exception. Water has a special property which is known as anomalous expansion of water. Because of this property, water when it freezes, its density becomes maximum value upto \[{{4}^{{}^\circ }}C\]. After that when the temperature of water changes from \[{{4}^{{}^\circ }}C\text{ to }{{\text{0}}^{{}^\circ }}\text{C}\] the density of water decreases and hence water starts to expand. When water freezes, its molecules form a hexagonal structure and therefore its size expands. Water molecules contain two hydrogen atoms and one oxygen atom. Water molecules are held together by intermolecular force of attraction. In liquid state water molecules can freely move around the container. They do not have any specific arrangement. There is a force of attraction between the hydrogen atom of one water molecule and oxygen atom of another water molecule. Although this force is not that strong compared to O-O attraction.When the water begins to freeze into ice, the water molecules are held by H-O bonds. This bond is not as tight as an O-O bond. As the H-O force of attraction is present in ice, its size expands.Therefore, the statement saying water contracts on freezing is a false statement. Additional information: There are other substances which can expand upon freezing. They are:- Bismuth- Gallium- Acetic acidNote: - The anomalous expansion property of water helps to preserve the lives of aquatic plants and animals in cold climate. - The way this property protects marine life is that during cooling of water, it becomes very dense at \[{{4}^{{}^\circ }}C\]. Due to maximum density the water at the top layer reaches the bottom and the lightest water at the bottom of the water body comes to the top. This lightest layer at the top is the first one to get frozen. After the top layer is completely frozen, it will not allow the cold of the winter to reach the bottom. This is because water and ice are insulators. Hence protecting the aquatic lives.
Usually, when things freeze - in other words turn from a liquid into a solid - they shrink or get smaller. This is because, normally, if you make something hotter, it vibrates more. When it vibrates more, it tends to take up more space, so it tends to expand. So, logically, if you cool something down, then the particles should move more slowly, collide and bounce off one another less hard and less frequently, and therefore, on average, spend more time closer together, making the material shrink. Ice, on the other hand, is very unusual in that, as it gets colder, although the particles are certainly vibrating less for the reason explained above, it nonetheless expands or gets larger. The reason for this is due to the strange shape of water molecules. If you've ever seen a picture of a water molecule you'll know that it looks like a "Mickey Mouse" head, with an oxygen atom where Mickey Mouse's face is, and then two hydrogen atoms where his ears are. The oxygen atom is slightly negative, and the hydrogens are slightly positively charged, so water molecules tend to stick together forming what are called hydrogen bonds. Owing to the water molecule adopting that shape, the way water molecules tend to link together in the liquid state is to form a very open structure with big holes. That means, there's quite a lot of extra "empty" space. When water freezes, the molecules get themselves into the most stable configurations or positions that have the minimum amount of energy in the resulting ice crystal. It so happens that the arrangement of water molecules that best satisfies this requirement is one that takes up even more space. And so ice expands when it freezes. |
When water freezes it contracts
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