The physical and chemical properties of water: generalities and curiosities
Water is vital for life! It covers 70% of the planet, it is a simple molecule with complex properties. One of the few substances to exist in nature in all three forms: gas, liquid and solid. What are its properties and curiosities? Because water is a very curious compound in many physical and chemical aspects ...
Unlike most liquids:
- water expands as it solidifies,
- it contracts on fusion,
- it reaches its maximum density at 4 ° C,
- its viscosity decreases when compressed,
- it has unique electrical and thermal properties,
- it accumulates an abnormally high amount of heat,
- its boiling point is much higher than expected.
In the late 1700s, Lavoisier and Cavendish, separately, discovered that water consists of:
- flammable air (hydrogen) and
- vital air (oxygen)
In fact, water is made up of two hydrogen atoms and one oxygen atom.
H2O symbol: hydrogen oxide.
Atomic or molecular mass
Water is made up of one oxygen atom and two hydrogen atoms.
Oxygen: 16 grams.
Hydrogen: 2 * 1 grams.
Molar mass of water: 18 grams.
Each oxygen atom is attached to the two hydrogens by chemical bonds. Singularity of water: each oxygen atom has special relationships with the hydrogen atoms of neighboring molecules called hydrogen bonds:
- these connections are made and broken billions of times per second,
- they are responsible for forming networks of hexagons,
- the result is a sort of crystal-like arrangement, rather than a chaotic anarchy like most liquids,
- this explains why the water is abnormally stable.
1) Ice floats on water: the density of ice is 8% lower than that of liquid water.
This means that 8% of the mass of an ice cube is above the surface or larger view: 8% of the mass of icebergs is at the surface.
2) The water-ice passage is done with expansion: if the water occupies a constrained volume, the container is subjected to colossal pressure (more than 2000 bars).
Almost all liquids have the opposite property: they contract while solidifying.
3) 6-pointed stars: The snowflakes are shaped like 6-pointed stars. Water molecules organize themselves into hexagonal networks. There are 12 varieties of ice cream (see following articles).
The referential water of our physical measurement units
Temperature: by definition of the degree Celsius scale, under normal atmospheric pressure.
Melting point: 0 ° C
Boiling point: 100 ° C
By definition, calorie is the amount of heat required to raise the temperature of water from 14,5 to 15,5 ° C of 1 gram of distilled water.