Chapter 25 Nuclear Chemistry 25.3 Fission and Fusion 25.1 Nuclear Radiation 25.2 Nuclear Transformations 25.3 Fission and Fusion 25.4 Radiation in Your Life Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Where does the sun’s energy come from? CHEMISTRY & YOU Where does the sun’s energy come from? 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What happens in a nuclear chain reaction? Nuclear Fission Nuclear Fission What happens in a nuclear chain reaction? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Fission When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments. This process is called fission. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear 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. U Uranium-235 (fissionable) 235 92 Uranium-236 (very unstable) 236 Ba Barium-142 142 56 Kr Krypton-91 91 36 3 n 1 Neutron More neutrons are released by the fission. These neutrons strike the nuclei of other uranium-235 atoms, which causes a chain reaction. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Fission In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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

Nuclear reactors use controlled fission to produce useful energy. Nuclear Fission 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear reactors use controlled fission to produce useful energy. Nuclear Fission Nuclear reactors use controlled fission to produce useful energy. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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

How do fission reactions and fusion reactions differ? Nuclear Fusion Nuclear Fusion How do fission reactions and fusion reactions differ? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The energy emitted by the sun results from nuclear fusion. Fusion occurs when nuclei combine to produce a nucleus of greater mass. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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

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. The reaction also produces two positrons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Fusion Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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

Glossary 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 Bullet #2: it was “nuclear moderation” earlier; which is correct? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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

Electrons and the Structure of Atoms BIG IDEA 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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