|Why is fire hot? What is a nuclear bomb?
|Question Date: 2000-10-17|
Fire is hot because it burns things like wood and
gas that have a lot of energy. The energy of wood
and gas is chemical energy, from molecules that
have a lot of carbon and hydrogen atoms in them.
When these molecules react with oxygen, they get
changed into new molecules made up of the same
atoms that have carbon and hydrogen and oxygen
atoms in them. The new molecules don't have very
much chemical energy. But the energy is still
somewhere, because it can't be destroyed. The
extra energy is in heat.
A nuclear bomb is
a special unusual case where atoms actually get
destroyed, which gives off HUGE amounts of energy
plus new atoms that don't have as much energy as
the old atoms. You can search for things like
this on www.google.com. (good Internet search
That's a good question, because they are similar
in a way.Whenever you change matter (any kind of
stuff) it either requires some added energy, or
gives off extra energy. When water changes to
ice, it gives off a little energy. It's still the
same stuff and the same combination of elements.
It has just changed from a liquid to a solid.
When you change wood to ashes, it gives off so
much energy that you can feel it as heat. In this
case, the ashes are completely different from the
original wood with different combinations from
elements, and can not be changed back like ice to
A nuclear bomb involves another
kind of change. It involves changing a single
element itself by breaking atoms of that element
apart. This kind of change gives off a really
huge amount of energy in the form of an explosion.
Fire is the result of a chemical reaction between
a fuel and oxygen. When the fuel is carbon based
(like gasoline, etc.) We can generically write
this down by the following:
oxygen -> carbon dioxide + water
One way to
think about this is by the principle of
conservation of energy. To first think about
this, we must first realize that all molecules
have an associated energy with them, where the
amount of that energy is different for different
molecules. What this means is that in any given
process the total energy is still the same.
However, the principle does not say anything about
the form the energy has to be in. If we look at
the above reaction, we would find that the energy
of the products (the CO2 and water) have a lower
energy of fuel and oxygen. However, since energy
must be conserved, the extra energy is given off
as heat. It's that release of energy from the
chemical reaction that makes fire
There are two basic types of nuclear
bombs - fission and fusion. Atomic bombs are
based on nuclear fission. An atomic bomb is
primarily made up of the isotope plutonium 239.
If a neutron hits plutonium nuclei, it may start
the fission process where the nuclei is changed,
and some energy and another neutron are produced.
The neutron acts as a catalyst since it starts
the reaction but as one is taken, another is
produced. When this reaction goes on and on, it
is called a "chain reaction." Plutonium in itself
does not become dangerous until it reaches the
point of "critical mass" - meaning it is
relatively stable until the density of nuclei is
high enough such that neutrons can start a chain
reaction. However, if there is not enough mass,
the process will quickly die out. Surrounding the
plutonium are many explosive charges. To detonate
an atomic bomb, the explosive charges are
simultaneously fired and the explosion compresses
the plutonium into a smaller area. Now, when a
neutron is added, the nuclei are close enough such
that the fission process can proceed in a chain
reaction. As the nuclei are split, the result is
an incredible release of that atomic energy. The
bomb dropped on Nagasaki was an atomic
The other type of bomb is a hydrogen
bomb, or a fusion bomb. Here, hydrogen nuclei are
forced together such that they actually fuse and
form a helium nucleus. In this process, there is
again a huge release of energy from the reaction.
As it is difficult to get the hydrogen atoms to
fuse, an atomic fission bomb can be used to get
the hydrogen nuclei close enough together to
initiate the process. To give you an idea of how
much energy this type of reaction release, we can
think of the sun. This type of hydrogen fusion
reaction is the same process by which the sun (and
other stars) generate their heat and light.
Fire is hot because chemical bonds are being
broken between atoms in a material and in that
process some energy is released as heat (infrared
radiation) as well as visible light.
nuclear reaction, individual atoms such as
hydrogen can, under the right circumstances,
combine to form heavier atoms, such as helium, and
release a lot of energy. This is called fusion.
It turns out that you can't fuse atoms
with more protons than iron and get energy out.
On the other hand, you can break apart a heavy
atom, such as uranium or plutonium and get some
This is called
Conventional bombs and dynamite
make explosions by creating a fire that burns all
the fuel very quickly. A nuclear bomb is the
equivalent using nuclear energy instead of
chemical energy. The reaction is started and all
the nuclear fuel "burns" at once, causing a big
explosion. A fission bomb is created by getting a
critical mass of fissionable material in a small
volume. As an atom decays, it releases energy and
particles which cause more atoms to decay in a
chain reaction. A more powerful fusion bomb is
created by using a fission reaction to heat up
some radioactive hydrogen to hot enough
temperature to be able to fuse together and
thereby release a lot of energy.
aside, I believe nuclear power plants work by
using a controlled nuclear fission "fire" to turn
water into steam to drive an electric generator.
We don't have a fusion nuclear power plant yet
because it is very difficult to start a controlled
and sustained fusion reaction. Scientists are
working on it though. It would be very nice to
have fusion plants as there should be little or no
nuclear waste to deal with. We know it's
possible; nuclear fusion is what powers the Sun.
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