substance

Water

Water is a liquid substance exhibiting fluid dynamics, quantum effects, and crowd simulation properties.
24 related articles · 1 formulas · 6 who worked here

Description

Water (H₂O) is a polar compound with a bond angle of about 104.5°. Oxygen pulls electrons, acquiring a partial negative charge, while hydrogens become positive. The resulting hydrogen bonds create a dynamic network, making water an excellent solvent for many substances. Water reaches its maximum density at 4 °C, not at freezing; this leads to convective mixing, preventing water bodies from freezing solid.

History

In antiquity, water was considered one of the primary elements. In 1781, Henry Cavendish synthesized water; Lavoisier named its components hydrogen and oxygen. Gay-Lussac and Humboldt determined the volume ratio 2:1. In the 20th century, X-ray diffraction and neutron scattering revealed the structure of water and ice; high-pressure ice phases were discovered by Percy Bridgman. Quantum chemical models of hydrogen bonding were developed by John Pople.

How it works

The hydrogen bond in water has a partially covalent character (~10%) and energy of about 20 kJ/mol. Its directionality and saturation ensure a local tetrahedral structure, which makes ice have a more open packing and lower density. Upon melting, some bonds break, but short-range order persists. When heated from 0 to 4 °C, residual ordering collapses, increasing density. Quantum effects (proton tunneling) are important for the properties of heavy water and some ice phases.

In practice

A universal solvent for chemical reactions, heat carrier in cooling and heating systems, basis of biological fluids, key factor in Earth's climate system.

Fun fact

Hot water sometimes freezes faster than cold water — the mysterious Mpemba effect, for which there is still no clear explanation.

Concept graph →

Formulas

$$\mathcal{M} = \frac{v}{c_s}$$
Ratio of flow velocity to local speed of sound.
What is in the formula
\mathcal{M}variableMach number — mach number
vvariableflow velocity — velocity metre per second
c_svariablelocal speed of sound — speed of sound metre per second
\mathcal{m}=\frac{ωa}{c_s(a)} · 2607.16422v1

Related articles · 129

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Quantum Chemistry for Hundreds of Thousands of Atoms
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