What are the molecular properties of fluids

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The properties of liquids are partly similar to those of solids and partly to those of gases.

In liquids, the distance between the particles is variable, they are constantly changing. There is something in common with gases in which the particles are even more mobile. In solids, on the other hand, the distance between the particles is constant.

The particle distance between liquids and solids is (on average) smaller than that of gases, so liquids and solids are only slightly compressible. Gases, on the other hand, react to an increase in pressure with a significant reduction in volume.

Tab. 1
Particle distancesarrangementCompressibility
Solidsmallorderly fixed grid placeslow
liquidgenerally slightly larger than in solids, but variablelittle orderlow
gashighly variabledisorderedhigh

Energy and interaction

In a liquid, the kinetic energy of the particles is greatly reduced compared to a gas. The particles are held together in a bond by intermolecular forces of attraction. Depending on the structure of the substance, van der Waals forces, dipole-dipole forces or hydrogen bridges act between the molecules. The strength of the attractive forces determines the volatility and the boiling point of a substance.

Tab. 2
Relationship : >> ≈ <
Episode:Particles move at high speed in the available volume.Particles interact with surrounding particles, but still have enough kinetic energy to move freely against each other.Influence of the forces of attraction dominates. The mobility of the particles is limited to oscillations against each other.

Legend:: kinetic energy: intermolecular interaction

The interactions between the liquid particles are not completely overcome by temperature movement (kinetic energy) up to the boiling point. Nevertheless, the particle movement is so fast that liquids, unlike solids, do not take on a solid form: they adapt to their container.

Liquids and solids are collectively referred to as condensed phases.

Illustration of the mobility of particles