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substance Conditions

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Freezing (hardening) is a transition of the liquid or fused substance in a firm condition. Boiling is liquid transition in a gaseous state or steam. It concerns all substances, and not just water.

The Fused pig-iron hardens, or stiffens, at temperature nearby 1535°Р, and its condition at lower temperatures correctly name fallen asleep. Therefore the term "чрё=№трэшх" it is not necessarily connected with concept "§юыюф".

Freezing points (hardening) and substance boiling depend on pressure. Even so far as concerns water, terms "чрьхЁчрэшх" and "ъшяхэшх" are not always used in the usual value. For example, water will begin to boil at a room temperature if sharply to lower pressure of air. Therefore "ъшя Ёшщ" not always means "уюЁ ёшщ".

Even at normal pressure of air many substances boil at very low temperatures. Them we usually name gases. So, air consists basically of two gases - nitrogen and oxygen. Their usual gaseous state speaks that they begin to boil at temperatures much more below zero: -196°Р (nitrogen) and -183°Р (oxygen). Therefore even in the coldest corners of the Earth temperature above their boiling points, and, hence, they remain gases.


substance Conditions

To understand that such hardening and boiling, it is necessary to know, why substances take the form of a firm body, a liquid or gas. These forms are known as a substance condition. As a whole, at constant temperature the sizes and the form of a firm body do not change. A liquid, spreading, changes the form, but its volume remains invariable. And at gas constants are not neither volume, nor the form. Gas extends or compressed to fill volume or the form of a vessel occupied with it.

Almost all matter consists of atoms which are grouped in molecules. Molecules are in constant movement, and energy of their movement (kinetic energy) defines a substance condition - firm, liquid or gaseous. In a firm body at molecules of poorly kinetic energy, they fluctuate round the fixed points. Therefore the firm body keeps the form. Liquid molecules possess sufficient energy to overcome force of a mutual attraction. They can move and, thus, change the liquid form. Gas molecules possess the big kinetic energy and are almost free in the movement.


Transition a liquid - gas

Transition a liquid - gas Not all molecules of a liquid move with identical speed. Some of them dvizhutsja so quickly that are capable to get through a surface into air and to turn to gas, or steam. If, for example, you leave an open glass with water in a warm premise for some days, the water level will gradually go down, while the glass completely will not become empty. This process of evaporation occurring on a surface of a liquid, it is not necessary to confuse to boiling at which transformation into steam occurs in all weight of a liquid. As the substance condition depends on intensity of movement of its molecules, it can vary at change of kinetic energy of molecules. We, often change a substance condition, subjecting to its influence of heat (one of energy forms). When, for example, we boil water; It turns to gas - steam, - as heat forces all molecules to move so quickly that it is already not enough force of their mutual attraction to keep them together. As a result of a molecule disappear in the form of steam, water "ъшяш=". Usually it occurs at temperature 100°Р.


Transition gas - a liquid

Steam again turns to water at certain loss of heat. This phenomenon can be observed at long boiling of water in a teapot. Cold surfaces indoors become covered by a moisture as the part of formed steam gives to them warmly at contact. As a result of steam molecule slow down movement, and it turns to water. It is said that steam was condensed in a liquid state, and the phenomenon name "ъюэфхэёрчшхщ".

We wrongly consider the ferry white clubs at a teapot nouse, but the present steam cannot be seen. Visible clubs consist of the tiny droplets of water formed at condensation of steam when on an exit from a teapot it faces rather cold air.


Transition a liquid - firm substance

It is possible to force to pass a liquid in a firm condition, having taken away from it warmly. For this purpose it is enough to place of it in colder environment. At loss of heat of a molecule of a liquid slow down the movement and, eventually, cannot move any more, and simply fluctuate round the fixed points. With approach of this phase the liquid hardens, i.e. Turns to firm substance. For example, water freezes at temperature 0°Р.

The Majority of substances crystallise at transition from a liquid state in the firm. So, NaCl (table salt) forms crystals of the cubic form.

Heating up, firm substances can pass again in a liquid state as speed of movement of their molecules thus increases.

At heating of firm substance for the purpose of transformation into a liquid its temperature grows at the expense of heat absorption. But, having reached melting points, the substance temperature remains to a constant though process of absorption of heat proceeds. Warm, used for transformation of firm substance into a liquid, does not increase after achievement of a melting point and is called as the latent warmth of fusion. Only after all firm substance will pass in a liquid state, its temperature starts to grow again.


Steam formation

If to continue to heat up a liquid, its temperature will grow before boiling point achievement then remains invariable as transformation of a liquid into gas demands heat considerable quantity. Warm, used for liquid transition in a gaseous state, is called as warmth of steam formation. As soon as all substance will turn to steam, its temperature will grow again.

At gas cooling its temperature falls in the beginning. Then, after achievement of a boiling point of substance, gas gives the warmth of steam formation and passes in a liquid state at the same temperature. Only when all gas will turn to a liquid, the substance temperature starts to fall.

At the further cooling the temperature decreases to a liquid freezing point then it gives the latent warmth of fusion and passes in a firm condition at the same temperature. When all liquid hardens, the substance temperature starts to fall again.


Pressure

Though it is considered that water freezes at 0°Р, and begins to boil at 100°Р, it is true only in the conditions of normal atmospheric pressure. With pressure change the temperature of transition of substance from one modular condition in another varies also. For example, at pressure increase the temperature of thawing of ice or water freezing decreases. That is why so it is easy to slide on the fads on ice of a skating rink or the frozen lake. The weight of a body of the person through narrow edges of the fads with huge force presses on ice. The point of thawing of ice as a result decreases, and its temperature becomes insufficiently low that it remained in a firm condition, and ice under the fads instantly turns to water. When pressure upon water stops, it again quickly turns to ice.

With pressure change also the temperature of boiling of water also varies. For example, at low pressure it is easier to molecules to disappear in air, and water begins to boil at temperature below the usual.

Sometimes climbers complain that cannot make good tea highly in mountains. It occurs because the above you rise in mountains, the less thickness of a layer of air over you. Thus pressure falls, and water begins to boil at temperature, too low for extraction of all flavouring substances from tea leaves. The further heating will accelerate boiling process, but will not raise a water temperature.

The Boomerang effect is observed at kipjachenii waters in a pressure cooker. Steam formed at boiling of water, has no exit from this tight vessel, and pressure in it increases. Thus the temperature of boiling of water raises, and water remains in a liquid state, will not heat up yet to temperature above its usual boiling point.

The Principle of influence of pressure upon liquids and gases is used in refrigerators. In some of them the liquid with low temperature of boiling at first turns to steam at the expense of pressure reduction. It occurs in the pipes passing through the freezing chamber. Turning to steam, the coolant absorbs hidden warmly internal part of a refrigerator and its contents, thereby, cooling them. Then steam is compressed and turns back to a liquid. Thus the coolant gives the latent heat deduced outside through tubes, located on a back wall of a refrigerator.


Impurity

Sometimes for definition of unknown products of chemical reactions and experiences their freezing points and boiling are used. But such method is applicable only for pure substances as presence of impurity reduces temperature of freezing and raises boiling temperature. So, table salt addition to water reduces a point of its freezing. That is why in the winter of road salt. Salty water freezes at temperature -8°Р and more low, therefore while the temperature will not fall at least to this point, freezing does not occur.

Ldosoljanaja a mix at times is applied in quality "ю§ырцфр¦Ёхщ ёьхёш" for nizkotemperaturnyh experiences. When ice thaws, it absorbs the latent heat demanded for transformation, from the surrounding his environment, thereby, cooling it. Heat is thus absorbed so much that the temperature can fall more low -15°Р.


Why ice floats

Why ice floats the Majority of substances extend at heating and are compressed at cooling. For example, mercury in a thermometer rises on a narrow tube and shows rise in temperature. As mercury freezes at -39°Р, it is not necessary for the thermometers used in severe temperature conditions.

Water also extends at heating and is compressed at cooling. However in a range of cooling from approximately 4°Р to 0°Ра it extends. Water pipes if water in them has frozen in the winter can burst, and the big weights of ice were formed. Pressure of ice upon pipe walls happens enough for their rupture.


water Expansion

As water extends at cooling, the ice density (the firm form of water) is less, than at water in a liquid state. In other words, the given volume of ice weighs less, than the same volume of water. Therefore ice is formed on a surface of ponds and lakes.

Around Northern and southern poles of the Earth water freezes and forms icebergs. Some of these floating ice slopes have the impressive sizes. In 1956 in a southern part of Pacific ocean largest of icebergs known to the person has been found out. The area of its surface exceeded 31 000 km 2 .