25.3 fission and fusion > 1 copyright © pearson education, inc., or its affiliates. all rights...

25.3 Fission and Fusion >25.3 Fission and Fusion >

1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Chapter 25Nuclear Chemistry

25.1 Nuclear Radiation25.2 Nuclear Transformations

25.3 Fission and Fusion

25.4 Radiation in Your Life



Where does the sun’s energy come from?

CHEMISTRY & YOUCHEMISTRY & YOU

The sun is about halfway through its life cycle. It has been producing energy for about 5 billion years and is expected to continue to produce energy for about 5 billion more.



Nuclear FissionNuclear Fission

Nuclear Fission

What happens in a nuclear chain reaction?




When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments.

• This process is called fission.




The figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron.

• More neutrons are released by the fission.

• These neutrons strike the nuclei of other uranium-235 atoms, which causes a chain reaction.

UUranium-235(fissionable)

23592 U

Uranium-236(very unstable)

23692

BaBarium-142

14256

KrKrypton-91

9136

3 n10

Neutron




In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.




Nuclear fission can release enormous amounts of energy.

• The fission of 1 kg of uranium-235 yields an amount of energy equal to that produced when 20,000 tons of dynamite explode.

• An atomic bomb is a device that can trigger an uncontrolled nuclear chain reaction.




Nuclear reactors use controlled fission to produce useful energy.

• The reaction takes place within uranium-235 or plutonium-239 fuel rods.

• A coolant absorbs heat produced by the controlled fission reaction and transfers the heat to water, which changes to steam.

• The steam drives a turbine, which drives a generator that produces electricity.




Nuclear reactors use controlled fission to produce useful energy.



How does the fission of a uranium-235 nucleus cause a chain reaction?

When slow-moving neutrons bombard uranium-235, the atom splits and releases more neutrons. These neutrons then collide with more uranium atoms, and so on.



Nuclear FusionNuclear Fusion

Nuclear Fusion

How do fission reactions and fusion reactions differ?




The energy emitted by the sun results from nuclear fusion.

• Fusion occurs when nuclei combine to produce a nucleus of greater mass.






• In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei.






• In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei.

• The reaction also produces two positrons.




Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei.



Key ConceptsKey Concepts

In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.

Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart to form smaller nuclei.



Glossary TermsGlossary Terms

• fission: the splitting of a nucleus into smaller fragments, accompanied by the release of neutrons and a large amount of energy

• neutron moderation: a process used in nuclear reactors to slow down neutrons so the reactor fuel captures them to continue the chain reaction



Glossary TermsGlossary Terms

• neutron absorption: a process that decreases the number of slow-moving neutrons in a nuclear reactor; this is accomplished by using control rods made of a material such as cadmium, which absorbs neutrons

• fusion: the process of combining nuclei to produce a nucleus of greater mass



Electrons and the Structure of Atoms

• During fission and fusion, atoms change their chemical identity as the number of protons in their nuclei change.

• In fission, large nuclei split into two or more smaller nuclei.

• In fusion, smaller nuclei combine to form larger nuclei at extremely high temperature and pressure.

BIG IDEABIG IDEA



END OF 25.3END OF 25.3

25.3 fission and fusion > 1 copyright © pearson education, inc., or its affiliates. all rights...

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