Explosives are classified as
substances that undergo an exothermic reaction at
a very quick rate. These reactions are all
characterized by a higher quantity of gas phase
products than reactants. This increase in
particles as well as the increase in heat released
from the chemical bonds is what causes the
expansion (explosion) for conventional explosives.
For low explosives this means that the required
chemicals are available for combustion in the
explosive itself. This way the rate of combustion
is quick enough to provide an explosion if it is
kept in a small container (such as gun powder in a
gun barrel). High explosives in contrast can
either be a reaction that occurs between two
chemicals like in low explosives or a
decomposition of one chemical into multiple
chemicals. The increase in rate of combustion or
decomposition causes the energy released into the
particles and heat to move faster than the speed
of sound. Because the energy cannot be transferred
fast enough by the surrounding medium (air) the
energy is built up and passed along moving at the
maximum possible velocity for that medium (speed
of sound). It is this phenomenon that causes the
shock wave from explosions.
For thermonuclear devices the
primary source of energy released in the explosion
comes from the fission or fusion reaction that
takes as the bomb detonates. When compared to the
power of conventional bombs, the energy released
by a nuclear bomb easily dwarfs a normal bomb. For
example the first ever nuclear bomb dropped was
code named "Little Boy" and exploded with the
force of 15,000 tons of TNT. The largest nuclear
weapon every dropped was the "Tsar Bomba" and it
exploded with the force of 50 megatons of TNT. On
google earth you can still see the crater from
where it landed (as it blew away a good chunk of
an island). Originally the Tsar was intended to be
a 100 megaton bomb but it was scaled down due to
concerns of radiation fall out.
