Everyone knows that water can be found in nature in three states of aggregation - solid, liquid and gaseous. On melting, the transformation solid ice into a liquid, and upon further heating, the liquid evaporates, forming water vapor. What are the conditions for melting, crystallization, evaporation and condensation of water? At what temperature does ice melt or steam form? We will talk about this in this article.

It cannot be said that water vapor and ice are rare in Everyday life. However, the most common is the liquid state - ordinary water. Experts have found that our planet is more than 1 billion cubic kilometers of water. However, no more than 3 million km 3 of water belong to fresh water bodies. Enough a large number of fresh water "rests" in glaciers (about 30 million cubic kilometers). However, melting the ice of such huge blocks is far from easy. The rest of the water is salty, belonging to the seas of the oceans.

Water surrounds modern man everywhere, during most daily procedures. Many believe that water resources are inexhaustible, and humanity will always be able to use the resources of the Earth's hydrosphere. However, this is not the case. The water resources of our planet are gradually depleted, and in a few hundred years, fresh water on Earth may not remain at all. Therefore, absolutely every person needs to take care of fresh water and save it. After all, even in our time there are states in which water supplies are catastrophically small.

Water properties

Before talking about the melting temperature of ice, it is worth considering the main properties of this unique liquid.

So, water has the following properties:

• Lack of color.
• Lack of smell.
• Lack of taste (but quality drinking water tastes good).
• Transparency.
• Fluidity.
• The ability to dissolve various substances (for example, salts, alkalis, etc.).
• Water does not have its own permanent shape and is able to take the shape of the vessel into which it enters.
• The ability to be purified by filtration.
• Water expands when heated and contracts when cooled.
• Water can evaporate to become steam and freeze to form crystalline ice.

This list presents the main properties of water. Now let's figure out what are the features of the solid state of aggregation of this substance, and at what temperature ice melts.

Ice is hard crystalline substance, which has a rather unstable structure. It, like water, is transparent, colorless and odorless. Ice also has properties such as brittleness and slipperiness; it is cold to the touch.

Snow is also frozen water, but it has a loose structure and has White color. It snows every year in most countries of the world.

Both snow and ice are extremely unstable substances. It doesn't take much effort to melt the ice. When does it start melting?

In nature, solid ice exists only at temperatures of 0 °C and below. If the temperature environment rises and becomes more than 0 °C, the ice begins to melt.

At the melting temperature of ice, at 0 ° C, another process occurs - freezing, or crystallization, of liquid water.

This process can be observed by all inhabitants of the temperate continental climate. In winter, when the temperature outside drops below 0 °C, it often snows and does not melt. BUT liquid water, which was on the streets, freezes, turning into solid snow or ice. In the spring, you can see the reverse process. The ambient temperature rises, so the ice and snow melt, forming numerous puddles and mud, which can be considered the only disadvantage of spring warming.

Thus, we can conclude that at what temperature the ice begins to melt, at the same temperature the process of water freezing begins.

Quantity of heat

In a science such as physics, the concept of the amount of heat is often used. This value indicates the amount of energy required for heating, melting, crystallization, boiling, evaporation or condensation various substances. Moreover, each of these processes has its own characteristics. Let's talk about how much heat is required to heat ice under normal conditions.

To heat the ice, you must first melt it. This requires the amount of heat needed to melt solid. Heat equals the product of the mass of ice and the specific heat of its melting (330-345 thousand Joules / kg) and is expressed in Joules. Suppose we are given 2 kg of solid ice. Thus, in order to melt it, we need: 2 kg * 340 kJ / kg = 680 kJ.

After that, we need to heat the resulting water. The amount of heat for this process will be a little more difficult to calculate. To do this, you need to know the initial and final temperature of the heated water.

So, let's say that we need to heat the water resulting from the melting of ice by 50 ° C. That is, the difference between the initial and final temperatures = 50 °C (initial water temperature - 0 °C). Then you should multiply the temperature difference by the mass of water and its specific heat capacity, which is equal to 4,200 J * kg / ° C. That is, the amount of heat required to heat water = 2 kg * 50 °C * 4,200 J*kg/°C = 420 kJ.

Then we get that for the melting of ice and the subsequent heating of the resulting water, we need: 680,000 J + 420,000 J = 1,100,000 Joules, or 1.1 Megajoules.

Knowing at what temperature ice melts, you can solve many difficult problems in physics or chemistry.

Finally

So, in this article, we learned some facts about water and its two states of aggregation - solid and liquid. Water vapor, however, is an equally interesting object to study. For example, our atmosphere contains approximately 25*10 16 cubic meters of water vapor. In addition, unlike freezing, the evaporation of water occurs at any temperature and is accelerated when it is heated or in the presence of wind.

We learned at what temperature ice melts and liquid water freezes. Such facts will always be useful to us in everyday life, since water surrounds us everywhere. It is important to always remember that water, especially fresh water, is an exhausting resource of the Earth and needs to be treated with care.

The same substance real world may be in different states depending on the environment. For example, water can be in the form of a liquid, in the idea solid body- ice, in the form of gas - water vapor.

• These states are called aggregate states of matter.

Molecules of a substance in different states of aggregation do not differ from each other. specific state of aggregation is determined by the arrangement of molecules, as well as the nature of their movement and interaction with each other.

Gas - the distance between molecules is much larger than the size of the molecules themselves. Molecules in a liquid and in a solid are quite close to each other. In solids even closer.

To change the aggregate body condition, he needs to give some energy. For example, in order to convert water into steam, it must be heated. In order for steam to become water again, it must give up energy.

The transition from solid to liquid

The transition of a substance from a solid to a liquid state is called melting. In order for the body to begin to melt, it must be heated to a certain temperature. The temperature at which a substance melts is called the melting point of the substance.

Each substance has its own melting point. For some bodies it is very low, for example, for ice. And some bodies have a very high melting point, for example, iron. In general, the melting of a crystalline body is a complex process.

ice melt chart

The figure below shows a graph of the melting of a crystalline body, in this case ice.

• The graph shows the dependence of the temperature of the ice on the time that it is heated. Temperature is plotted on the vertical axis, time is plotted on the horizontal axis.

From the graph, the initial temperature of the ice was -20 degrees. Then they started to heat it up. The temperature started to rise. Section AB is the section of ice heating. Over time, the temperature increased to 0 degrees. This temperature is considered the melting point of ice. At this temperature, the ice began to melt, but at the same time its temperature ceased to increase, although the ice also continued to heat up. The melting area corresponds to the BC section on the graph.

Then, when all the ice melted and turned into a liquid, the temperature of the water began to increase again. This is shown on the graph by ray C. That is, we conclude that during melting, the body temperature does not change, All incoming energy is used for heating.

Motion. Warmth Kitaygorodsky Alexander Isaakovich

The influence of pressure on the melting point

If the pressure is changed, the melting point will also change. We met with the same regularity when we talked about boiling. The higher the pressure, the higher the boiling point. As a rule, this is also true for melting. However, there are a small number of substances that behave anomalously: their melting point decreases with increasing pressure.

The fact is that the vast majority of solids are denser than their liquids. The exception to this rule is precisely those substances whose melting point does not change quite normally with a change in pressure - for example, water. Ice is lighter than water, and the melting point of ice decreases as pressure increases.

Compression promotes the formation of a denser state. If a solid is denser than a liquid, then compression helps solidify and prevents melting. But if melting is hindered by compression, then this means that the substance remains solid, whereas earlier at this temperature it would have already melted, i.e. as the pressure increases, the melting point rises. In the anomalous case, the liquid is denser than the solid, and the pressure helps the formation of the liquid, i.e. lowers the melting point.

The effect of pressure on the melting point is much less than that of boiling. An increase in pressure by more than 100 kg/cm 2 lowers the melting point of ice by 1 °C.

From here, by the way, it is clear how naive is the often encountered explanation of the sliding of skates on ice by a decrease in the melting temperature due to pressure. The pressure on the blade of the skate, in any case, does not exceed 100 kg/cm 2 , and for this reason a decrease in the melting point cannot play a role for skaters.

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