25.3. Lesson 25.3 Fission and Fusion. Overview. In this lesson, you will cover the topics of nuclear fission and fusion and nuclear reactors.

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1 25.3 Lesson 25.3 Fission and Fusion Objectives Lesson Links Describe what happens in a nuclear chain reaction Distinguish fission reactions from fusion reactions. Ch. 25 Core TR: Section 3 Review Ch. 25 Small Scale Lab 41: Half-Lives and Reaction Rates 25.3 Lesson Overview (PowerPoint file) 25.3 Kinetic Art: How a Nuclear Reactor Works Chapter 25 Online Student Edition Study WB Chapter 25 Lesson 3 Overview/Materials Overview In this lesson, you will cover the topics of nuclear fission and fusion and nuclear reactors. Classroom Materials Standard 1 Block 0.5 Nuclear Fission: wooden matchsticks Standard There are no items. Chemistry & You Engage Explain that about 92% of all the sun's atoms are hydrogen. The second most abundant element is helium. Ask What can you infer about the reactant and product of the nuclear reaction that takes place in the sun? (Hydrogen is the page 1 of 6

2 reactant and helium is the product.) Activate Prior Knowledge Engage Have students brainstorm examples of chain reactions, such as a multi-car accident on an icy highway. Have students consider how these chain reactions often result in a significant number of collisions from the single initial collision, and energy inputs and transfers are required for the collisions to proceed. Nuclear Fission Explain Figure Display Figure and explain that uranium-235 is called a fissionable material because its nucleus becomes unstable when it is struck by a neutron. Ask the students to hypothesize why enormous amounts of energy are released in the reactions Kinetic Art: How a Nuclear Reactor Works Note that three neutrons are produced by each fission event. Explain that fission reactions also produce radioactive waste products such as krypton-91 and barium Have students draw a diagram showing how the neutrons from a single fission process can induce subsequent fissions in other uranium-235 nuclei. The diagrams should illustrate the exponential nature of fission. Explain that this process is called a chain reaction because once it is triggered, the reaction will continue without outside intervention. Have the students explain why the reactions become exponentially larger. Have the students work through 25.3 Kinetic Art: How a Nuclear Reactor Works on PearsonChem.com and complete the accompanying questions. Discuss neutron moderation and absorption to make sure the students understand the whole process in nuclear reactors. Explain that the wastes produced in fission reactors contain isotopes with half-lives page 2 of 6

3 measured in the thousands or hundreds of thousands of years. Many proposals for storing or disposing of these wastes involve methods and materials that may be highly unsuitable. For example, the placement of wastes in thick drums that would then be sunk in the oceans one suggested method may contain the waste for only decades or a few centuries. The containers would begin to leak long before the contents were safe. The U.S. Department of Energy is responsible for cleaning up 130 nuclear sites and safely managing their waste. The sites include locations where uranium was milled, research labs, and former nuclear weapons production facilities. Have students research how the cleanups are progressing and how and where the nuclear waste is being disposed. Nuclear Fission Explore Cut some matchsticks in half and arrange the heads in branching chains on a noncombustible surface. The end of each matchstick should touch the heads of two other matchsticks, forming a "Y". Ignite the first matchstick head. The match will ignite a chain reaction Safety Keep all flammable materials away from the demo area. Have a fire extinguisher ready. Materials: wooden matchsticks Nuclear Fission Explain Display Figure and ask the students to explain how fusion reactions differ from fission reactions. Explain that the figure shows the reaction that occurs in the sun and is the reason that the sun shines. Tell the students that fusion is an appealing source of energy because the potential fuels are inexpensive and the amount of radioactive waste produced is theoretically minimal. page 3 of 6

4 Nuclear Fusion Extend Generate a discussion about the limitations of using fusion as an alternative energy source. Point out that the only known way of generating the necessary heat to start a fusion reaction is to use a fission bomb an uncontrolled reaction. Currently, no known materials or engineering designs exist that could withstand either the temperatures or the necessary fission-generated explosion. As a result, scientists have been pursuing the possibility of finding a situation in which fusion would occur at room temperature, a process called cold fusion. Have students research the history and current state of cold fusion research, and present a report explaining their findings. Assess and Remediate Evaluate Ask students to write nuclear equations describing fission and fusion. Chapter 25 Online Student Edition Ask How might a meltdown of a nuclear reactor occur? (Rapid removal of the control rods could allow too many neutrons to react with fissionable nuclei.) Ask Describe the conditions under which nuclear fusion will occur. (Temperatures in excess of 4.0 x 10 7 C; methods to confine and control the reaction are needed.) Then, have the students complete the 25.3 Lesson Check. Remediate Explain that both nuclear fission and nuclear fusion produce energy by the conversion of matter to energy. In fission, heavy nuclei are split into lighter nuclei. In fusion, light nuclei combine to form heavier nuclei. Fission reactions are relatively easy to control but produce radioactive wastes. Fusion reactions are difficult to initiate and control but produce little radioactive waste. Guide students in creating a concept map to help them organize the content in the page 4 of 6

5 lesson. Differentiated Instruction Struggling Students After preparing the match demonstration, allow students to examine the matchstick chain. Project Figure on the board, and identify parts of the chain that are equivalent to components of the U-235 reaction. Figure Ch. 25 Core TR: Section 3 Review Study WB Chapter 25 Lesson 3 Less Proficient Readers Explain that the term fission is generally used when an object splits into smaller parts. Demonstrate fission using rock candy crumbling into small pieces. Relate the concept of fission to fragmenting, breaking up, or crumbling. Explain that the term fusion is generally used when an object combines into a larger whole. Demonstrate fusion using popcorn pieces that are joined together to make a popcorn ball. Relate the concept of fusion to merging or joining together. Advanced Students Explain that the difference between the mass of a nucleus and the masses of the separated protons and neutrons is called the mass defect. Challenge students to use the mass defect and Albert Einstein's famous equation, E = mc 2, to calculate the energy released during a fission reaction. Focus on ELL and Language Have students write the definitions of fission and fusion in their notebooks in their native language and in English. Have students prepare a two-column table to use to compare and contrast these two processes. Encourage them to record sample reactions and characteristics of each process as they progress through the lesson. Have the students preview Figure and Figure and identify any similarities and differences that they find. Have them add these characteristics to their table. Figure Figure Ch. 25 Core TR: Section 3 Review Study WB Chapter 25 Lesson 3 page 5 of 6

6 My Notes Homework page 6 of 6