Nuclear Reaction: Definition & Examples

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  • 0:06 Nuclear Reactions vs.…
  • 0:42 Chemistry Review and…
  • 2:58 Fission
  • 4:10 Fusion
  • 4:49 Lesson Summary
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Lesson Transcript
Instructor: Amy Meyers

Amy holds a Master of Science. She has taught science at the high school and college levels.

Learn the differences between a nuclear reaction and a chemical reaction. Also learn how the nuclear reaction involves subatomic particles including protons and neutrons. Discover the different types of nuclear reactions including fission and fusion and also how a nuclear power plant works to produce energy.

Nuclear Reactions vs. Chemical Reactions

A nuclear reaction, very simply, is a reaction that affects the nucleus of an atom. This is different from a chemical reaction, which has nothing to do with the nucleus of an atom but rather involves changes in atoms' electrons that orbit the nucleus. In chemical reactions, the electrons are exchanged from one or more substances to produce a different substance, and the elements are the same in the products and reactants. In nuclear reactions, the particles in the nucleus are changed, and one element is transformed into another element when particles in the nucleus are gained or lost.

Chemical reactions involve the electrons in an atom, whereas nuclear reactions involve the nucleus
Chemical Reactions

Chemistry Review and Terminology

Let's do a little review of chemistry. An atom contains a nucleus where the protons and neutrons live surrounded by a cloud of electrons. These electrons live in energy shells around the nucleus. The atom is most stable when its outer shell is full. Atoms like to be stable. They work very hard to reach a level where their outer shells of electrons are filled by combining with other atoms and losing or gaining electrons. That is for chemical reactions. But as I said, nuclear reactions deal with the particles in the nucleus itself. These particles are called subatomic particles.

When we talk about nuclear reactions some of the terminology changes. The atom is now called the nuclide and we talk about how many protons and neutrons it has in its nucleus. The mass number is the sum of the protons and neutrons in the nucleus, and the atomic number is the number of protons in the nucleus. Nuclides are represented in one of two ways: either as 228 88 Ra, where the superscript is the mass number and the subscript is the atomic number; or as radium-228, where the number refers to the mass number.

In nuclear reactions, unstable nuclei spontaneously undergo changes to their numbers of protons and neutrons, giving off a lot of energy in the process and making themselves more stable. There are four types of nuclide emissions they can give off:

  • Alpha particle, which has a charge of +2
  • Beta particle, which has a charge of -1
  • Positron, which has a charge of +1
  • Gamma ray, which has a charge of 0

In an equation showing a nuclear reaction, the total of the atomic numbers and the total of the mass numbers must be equal on both sides of the equation: 4 11H nuclei = 42He nucleus + 2 Beta particles + energy. The beta particle is one of the types of nuclide emissions and equals a -1 charge.

Nuclear reactions result in much larger energy changes than chemical reactions. For example, one gram of deuterium that is present in about 30 liters of sea water would produce as much energy as 9000 liters of gasoline.

Compared to chemical reactions, nuclear reactions result in much larger energy changes
Nuclear and Chemical Reaction Comparison


There are two main types of nuclear reactions, fission and fusion. Nuclear fission is when the nucleus of a large atom is split into two or more fragments. This releases neutrons and energy. Nuclear fission can occur spontaneously, or it can be started when nuclei are hit by particles. When the nuclei are hit, neutrons are blown out of them. These neutrons go on to hit other nuclei, which release more neutrons, and a chain reaction has started. The chain reaction continues until all of the nuclei are split and all of the atoms are stable again. In nuclear fission, when a larger atom breaks apart, the mass of the two products is less than the mass of the original atom. This mass is lost in the form of energy. This is know from Einstein's famous E = mC^2, which says that mass and energy are directly proportional. A loss in one equals a gain in the other.

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