السوائل - الطاقة الكيميائية .. الفيزياء

Liquids - Chemical Energy .. Physics

Liquids

When the temperature of a gas decreases, the average energy of its molecules decreases until it reaches a weak level, and it is difficult for them to overcome the forces of attraction between them, so they circle around each other in multiple groups, and their random movement decreases as a result. However, these groups remain able to slide over each other, and take the shape of the container in which they are located, and the body then becomes a liquid.

The molecules in liquids are in constant motion, so the part of them close to the surface of the liquid, which is characterized by its speed, is allowed to escape from the bonds that bind it to the adjacent section, which causes a decrease in volume and a type of evaporation occurs. The pressure of the free molecules is called the vapor pressure of the liquid, whose value does not change unless its temperature changes, so it increases with its rise, until it eventually becomes equal to atmospheric pressure, when the temperature of the liquid reaches the boiling point.

Although water is the most widespread liquid on the surface of the globe. The composition of it remained incomprehensible until relatively recently.

In its gaseous state (steam), it is composed of triatomic molecules. As for its liquid and solid states, additional forces are formed between its neighboring molecules and are called hydrogen bonds. These are electrical attraction forces whose value does not exceed one-tenth of the value of covalent valence bonds. Their function is to link the positive hydrogen nucleus in the atom with the smallest negative charge in the oxygen atom that belongs to the neighboring molecule. It is known that this small charge is formed as a result of the tendency of the electrons in the molecule to circle around the oxygen atom. As for snow, tetrahedral shapes are formed in which the water molecule is surrounded by four identical molecules, in a structure that extends to infinity. These structures collapse completely when the snow melts, and disintegrate into molecules that reassemble around each other. This is what makes water heavier than the ice that floats on its surface. It should be noted that although these tetrahedral bodies break down during the melting of ice, small clusters of molecules remain as long as the temperature does not reach 4 °C. After that, the density follows its usual rule and decreases as the temperature rises. For this reason, water has an unusual property, which is that its density reaches its maximum at a temperature of 4 °C. Hydrogen bonds continue to hold water molecules together until boiling begins at 100 °C. (Hydrogen bonds between water molecules form an open network structure (above) Fish live under the ice that floats on the surface of the water (below).