http://www.ck12.org Chapter 11. Nuclear Chemistry
fission and nuclear fusion produce so much energy.
FIGURE 11.18
Albert Einstein is considered by many to be the greatest physicist of all
time.You can listen to a recording of Einstein explaining his famous equation at this URL: http://www.youtube.com/w
atch?v=CC7Sg41Bp-U.
What Einstein’s Equation Means
In Einstein’s equation, the variableEstands for energy and the variablemstands for mass. Thecin the equation is
a constant. It stands for the speed of light. The speed of light is 300,000 kilometers (186,000 miles) per second, so
c^2 is a very big number, no matter what units are used to measure it. Einstein’s equation means that the energy in a
given amount of matter is equal to its mass times the square of the speed of light. That’s a huge amount of energy
from even a tiny amount of mass. Suppose, for example, that you have 1 gram of matter. That’s about the mass of a
paperclip. Multiplying that mass by the square of the speed of light yields enough energy to power 3,600 homes for
a year!
Mass and Energy in Nuclear Reactions
When the nucleus of a radioisotope undergoes fission or fusion, it loses a tiny amount of mass. What happens to the
lost mass? It isn’t really lost at all. It is converted to energy. How much energy?E=mc^2. The change in mass is
tiny, but it results in a great deal of energy.
What about the laws of conservation of mass and conservation of energy? Do they not apply to nuclear reactions?
We don’t need to throw out these laws. Instead, we just need to combine them. It is more correct to say that the sum
of mass and energy is always conserved in a nuclear reaction. Mass may change to energy, but the amount of mass
and energy combined remains the same.
Lesson Summary
- Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This releases a great deal of
energy. Nuclear power plants use the energy from nuclear fission to generate electricity. - Nuclear fusion is the fusing of two or more smaller nuclei to form a single, larger nucleus. Fusion releases
even more energy than fission. Researchers are trying to find a way to use the energy from nuclear fusion to
generate electricity.