• Why does water freeze?

    Human life has always depended, and will depend on water. That is why from time immemorial people watched her very carefully. They found that in cold weather, water freezes, turning into a solid - ice, which when heated again becomes liquid, that is, water. How does this happen, why does water freeze, becoming ice?

    What is crystallization?

    Most substances on the planet, both natural and artificial, can be in several aggregative (phase) states. These are the forms of their existence, which can replace each other. Change of forms depends on external conditions. In nature, there are 3 states of matter - gaseous, liquid and solid.

    More than 80% of the water on our planet is in a liquid state. This suggests that water molecules move quickly and have a weak connection between them. For these reasons, water can take any form, but it cannot save it.

    But if the liquid is cooled, then it becomes solid. The speed of movement of its molecules can slow down so much that a stable bond is established between them. It turns out a solid body that has its own internal structure.When the structure is ordered, then it is called crystalline. In this case, ice is a crystalline substance. Ice crystals are hexahedral.

    The transition of a substance from a liquid to a solid is called crystallization or solidification. The reverse process, that is, the transition from a solid to a liquid � by melting.

    0 degrees on the Celsius scale was set to the freezing temperature of fresh

    What is the Mpemba Effect?

    The paradox that crystallization in hot water occurs earlier than in cold water is known as the �Mpemba Effect�. There are several options explaining why hot water freezes faster than cold water. Consider some of these options:

    1. Hot water has more crystallization centers than cold water. And with their small amount it becomes difficult to transition to a solid state.

    2. Cold water starts to freeze from above. This also worsens the processes of convection and radiation. Hot water freezes to the bottom. That is, the heat transfer from hot water is higher than that of cold.

    3. Hot water evaporates faster. This reduces its volume. And water with a smaller volume will freeze faster.

    4.If there is a snow lining under the container with hot water, then it thaws, and the thermal contact between the container and the cooling surface is improved. Thus, heat transfer increases. Under the container with cold water, the snow does not melt.

    Why salt water does not freeze?

    Water freezes (crystallizes) at any salinity. Just the freezing point of such water below. For example: distilled water, in which there is no salt, freezes at 0 * C; water, where 2 g of salt is dissolved in 1 liter, freezes at -0.1 * �; ocean water (35 g of salt / 1l) begins to freeze at -1.9 * �.

    In this case, only water is crystallized, and the brine itself has an even lower freezing point. That's why the arctic ice is always fresh.


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