Water is one of the most amazing substances. Despite the wide distribution and widespread use, it is a real mystery of nature. Being one of the oxygen compounds, water, it would seem, should have very low characteristics such as boiling and freezing temperatures , heat of vaporization, etc. But this does not happen. In spite of everything, the heat capacity of water alone is extremely high.
Water is capable of absorbing a huge amount of heat, while at the same time practically without heating - this is its physical feature. The specific heat of water is about five times higher than the heat of sand, and ten times that of iron. Therefore, water is a natural cooler. Its ability to accumulate a large amount of energy makes it possible to smooth out temperature fluctuations on the Earth's surface and to regulate the thermal regime within the entire planet, and this happens regardless of the time of year.
This unique property of water allows its use as a cooling substance in industry and in everyday life. In addition, water is a widely available and relatively cheap raw material.
What is meant by heat capacity? As is known from the course of thermodynamics, heat transfer always occurs from a hot to a cold body. In this case, we are talking about the transition of a certain amount of heat, and the temperature of both bodies, being a characteristic of their state, shows the direction of this exchange. In the process of heat exchange, for example, of a metal body with water of equal mass at the same initial temperatures, the metal changes its temperature several times more than water.
If we take as a postulate the main assertion of thermodynamics - from two bodies (isolated from the others), when one gives off and the other receives an equal amount of heat, it becomes clear that metal and water have completely different heat capacities.
Thus, the heat capacity of water (as well as of any substance) is an indicator characterizing the ability of a given substance to give (or receive) a certain amount of heat when it cools ( heats ) per unit temperature.
The specific heat of a substance is the amount of heat required to heat a unit of this substance (1 kilogram) by 1 degree.
The amount of heat generated or absorbed by the body is equal to the product of the specific heat, mass and temperature difference. It is measured in calories. One calorie is exactly the amount of heat that is enough to heat 1 g of water per 1 degree. For comparison: the specific heat of air is 0.24 cal / g ∙ ° , aluminum - 0.22, iron - 0.11, mercury - 0.03.
The heat capacity of water is not constant. With an increase in temperature from 0 to 40 degrees, it decreases slightly (from 1.0074 to 0.9980), while for all other substances this characteristic increases during heating. In addition, it can decrease with increasing pressure (at depth).
As you know, water has three states of aggregation - liquid, solid (ice) and gaseous (steam). In this case, the specific heat of ice is about 2 times lower than that of water. This is the main difference between water and other substances, the specific heat of which does not change in the solid and molten state. What is the secret?
The fact is that ice has a crystalline structure, which, when heated, does not collapse immediately. Water contains small particles of ice, consisting of several molecules and called associates. When water is heated, part of the thermal energy is spent on the destruction of hydrogen bonds in these formations. This explains the unusually high heat capacity of water. The bonds between its molecules are completely destroyed only when water passes into steam.
The specific heat capacity of water vapor at a temperature of 100 ° almost does not differ from that of ice at 0 ° . This once again confirms the correctness of this explanation. The heat capacity of steam, as well as the heat capacity of ice, has now been studied much better than water, for which scientists have not yet come to a consensus.