CK-12 Physical Science - For Middle School

http://www.ck12.org Chapter 11. Nuclear Chemistry

11.3 Nuclear Energy

Lesson Objectives

• Describe nuclear fission and how it is used for energy.


• Describe nuclear fusion and challenges to its use for energy.


• Relate nuclear energy to Einstein’s equation,E=mc^2.

Lesson Vocabulary

• nuclear energy


• nuclear fission


• nuclear fusion

Introduction

Nuclear energyis the energy released in nuclear reactions. Two types of reactions that release huge amounts of
energy are nuclear fission and nuclear fusion.

Energy from Nuclear Fission

Nuclear fissionis the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a
great deal of energy from a very small amount of matter. For example, nuclear fission of a tiny pellet of uranium-235,
like the one pictured inFigure11.11, can release as much energy as burning 1,000 kilograms of coal!

Nuclear fission of uranium-235 can be represented by this equation:

235

92 U+1 Neutron→

92

36 Kr+

141

56 Ba+3 Neutrons+Energy

As shown inFigure11.12, the reaction begins when a nucleus of uranium-235 absorbs a neutron. This can happen
naturally or when a neutron is deliberately crashed into a uranium nucleus in a nuclear power plant. In either case, the
nucleus of uranium becomes very unstable and splits in two. In this example, it forms krypton-92 and barium-141.
The reaction also releases three neutrons and a great deal of energy.

Nuclear Chain Reaction

The neutrons released in this nuclear fission reaction may be captured by other uranium nuclei and cause them to
fission as well. This can start a nuclear chain reaction (seeFigure11.13). In a chain reaction, one fission reaction