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KEY  TERMS:  Ch  9.4  Nuclear  Reactions  

•  Nuclear  Fission  –  the  process  of  splitting  a  nucleus  into  two  nuclei  with  smaller  masses  

•  Chain  reaction  –  ongoing  series  of  fission  reactions  •  Critical  mass  –  the  amount  of  fissionable  material  required  so  that  each  fission  reaction  produce  approximately  one  more  fission  reaction  

•  Nuclear  Fusion  –  two  nuclei  with  low  masses  are  combined  to  form  one  nucleus  of  larger  mass  

•  Fission and Fusion Video    

Nuclear Fission •  Fission means “to divide” •  The process of splitting a nucleus into two nuclei

with smaller masses •  This occurs when a neutron hits the nucleus of an atom

•  Only large nuclei can underdo fission reactions •  Two uses from book: generate electricity, nuclear

weapons •  The total mass of the products is slightly less than the

mass of the original nuclear and the neutrons that break free •  The missing mass is converted into large amounts of

energy

Nuclear Fission

Neutron Uranium - 235

Lighter element

Lighter element

Neutrons + Energy

Nuclear Fission •  Chain reactions are continuing series of reactions in which each

produces a product that can react again •  If chain reaction occurs too quickly, explosions occur, releasing a lot

of energy all at once

energy

energy

energy

energy

energy

energy

Fission of Uranium-238

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Nuclear Fusion •  Fusion = combine •  Nuclear Fusion is when two or more nuclei combine to

form a larger nucleus (requires very high temps to overcome the repulsive forces)

•  The sun uses this process to produce energy •  It fuses hydrogen into helium •  The problem lies in the energy involved to start fusion •  Most nuclei that can undergo fusion are fairly unreactive •  Energy given off (output) does not outweigh the energy needed

(input)

•  Hydrogen Bomb •  Just like in fission, a small amount of mass is converted

into a large amount of energy

Fusion of Hydrogen into helium

Nuclear Fusion

energy

energy

neutrino

positron

neutrino

positron

Energy to Mass Conversions •  Think back to the law of conservation of energy •  We need to include mass in this law when talking

about fission and fusions reactions •  This relationship is shown by Einstein’s theory of

relativity •  This states that energy and mass are equivalent and

can be converted using the equation E=mc2

Warm-Up 1.  What type of nuclear reaction shown below? 2.  Write an equation for the reaction. You only need to

include the symbol and mass number.

3.  What type of nuclear reaction is shown below?