Helium
(He)
Helium is the second
lightest element and is the second most abundant element in the
universe, being present at about 24% of the total elemental
mass. When Helium is liquefied
it
is the coldest liquid known and can exhibit some unique properties,
such as negative surface tension.
Physical
properties
Phase at STP
Gas
Melting
point
0.95 K (−272.20 °C, −457.96 °F) (at 2.5 MPa)
Boiling
point
4.222 K (−268.928 °C, −452.070 °F)
Density (at
STP)
0.1786 g/cm3
Other Properties
Speed of Sound: 972 m/s
Thermal Conductivity: 0.1513 W/(m·K) [at room temperature]
Example uses of helium
Used
as an inert non reactive gas for a range of
industrial applications, e.g. welding
Used as a coolant in super conducting electromagnets magnets
Used in airships and party balloons to cause buoyant lift
Used as a diving mix gas to reduce the effect of nitrogen narcosis with
depth
Used as a coolant gas within some light bulbs
Can be used to ease breathing for some hospital patients, e.g.
asthmatics due
to the low density of the gas (this can make breathing easier)
Helium is used to purge the gas tanks of spacecraft using liquid
propellants,
e.g. liquid hydrogen and liquid oxygen as helium gas will not liquefy
and hence
provide an inert gas blanked over these volatile fuels
The following videos show some chemistry experiments and
demonstrations relating to Helium
This
video is a demonstration showing some of
the characteristic properties associated with Helium
Due to the low density of helium and
the increased speed of
sound through this gas, when compared to normal air, inhaling helium
raises the
pitch of your voice. Care should be exercised if performing this
experiment;
inhaling helium displaces oxygen and without sufficient oxygen in our
lungs an
insufficient amount of oxygen is transferred into the blood stream-
this can
result in unconscious or even death.
Helium
(He)