A liquid will usually assume the shape of its container
A diagram of how the configuration of molecules/atoms differs for the solid, liquid, and gas phases.
A 'liquid' is one of the four principle
states of matter. A liquid is a
fluid that can freely form a distinct surface at the boundaries of its bulk material.
Characteristics
A liquid's shape is determined by, but not confined to, the container it fills. That is to say, liquid particles (normally
molecules or clusters of molecules) are free to move within the volume, but they form a discrete surface that may not necessarily be the same as the vessel. The same cannot be said about a
gas; it can also be considered a fluid, but it ''must'' conform to the shape of the container entirely.
At a temperature below the boiling point, a liquid will evaporate until, if in a closed container, the concentration of the vapors belonging to the liquid reach an equilibrium
partial pressure in the gas. Therefore no liquid can exist permanently in a
vacuum. The surface of the liquid behaves as an elastic membrane in which
surface tension appears, allowing the formation of
drops and
bubbles.
Capillarity is another consequence of
surface tension. Only liquids can display
immiscibility. The most familiar mixture of two immiscible liquids in everyday life are the
vegetable oil and
water in Italian salad dressing. A familiar set of miscible liquids are water and alcohol. Only liquids display
wetting properties. Liquids at their respective
boiling point change to
gases (except when
superheating occurs), and at their
freezing points, change to
solids (except when
supercooling occurs). Even below the boiling point liquid
evaporates on the surface. Objects immersed in liquids are subject to the phenomenon of
buoyancy, which is also observed in other fluids, but is especially strong in liquids due to their high density. Liquid components in a mixture can often be separated from one another via
fractional distillation.
The
volume of a quantity of liquid is fixed by its
temperature and
pressure. Unless this volume exactly matches the volume of the container, a surface is observed. Liquids in a gravitational field, like all fluids, exert pressure on the sides of a container as well as on anything within the liquid itself. This pressure is transmitted in all directions and increases with depth. In the study of fluid dynamics, liquids are often treated as
incompressible, especially when studying
incompressible flow.
If a liquid is at rest in a uniform
gravitational field, the
pressure at any point is given by
:
where:
:
= the
density of the liquid (assumed constant)
:
=
gravity
:
= the depth of the point below the surface.
Note that this formula assumes that the pressure ''at'' the free surface is zero, and that
surface tension effects may be neglected.
Liquids generally expand when heated, and contract when cooled.
Water between 0 °C and 4 °C is a notable exception; this is why
ice floats. Liquids have little
compressibility : water, for example, does not change its
density appreciably unless subject to pressure of the order of hundreds bar.
Examples of everyday liquids besides water are
mineral oil and
gasoline. There are also mixtures such as
milk, blood, and a wide variety of aqueous solutions such as household
bleach. Only six elements are liquid at room temperature and pressure:
bromine,
mercury,
francium,
cesium,
gallium and
rubidium.
[1] In terms of
planetary habitability, liquid water is required for the existence of
life.
Liquid measures
Quantities of liquids are commonly measured in units of
volume. These include the litre, not an
SI unit, and the
cubic metre (m³) which is an SI unit.
See also
★
Ripple effect
★
Multiphasic liquid
★
Viscosity
★
Surface tension
★
Sonoluminescence, emission of short bursts of light from imploding bubbles in a liquid when excited by sound.
Notes
1. Liquid Elements
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