Nuclear Reactions Mass Defect Binding Energy

1
Nuclear ReactionsMass DefectBinding Energy

• Honors Chemistry
• Mrs. Coyle

Indian Point, NY
2
Part I

• Nuclear Reactions

3
Transmutations

• When a nucleus of an element is transformed to a
  nucleus of another element.

4
Transmutations

• Can occur through
• Decay (Spontaneously)
• Nuclear Reactions (Fusion and Fission)

5
Nuclear Reactions

• Fission
• Fusion

6
Nuclear Fission

• Enrico Fermi (USA) 1930s
• Lise Meitner, Strassman, Hahn (Germany)
• Bombarding neutrons at 235U or 239Pu causes
  fission (splitting) of the nucleus producing new
  neutrons that then cause more fission in a chain
  reaction.
• Huge amounts of energy (mostly kinetic energy of
  fragments) is released

7
Nuclear Fission
Chain Reaction
Neutron bombardment

• n 235U ? 236U ?XY n energy

8
Nuclear Fission

• 235U is a rather rare isotope(0.7) of the more
  abundant 238U which does not undergo fission.
• Nuclear Bomb
• Nuclear Power Plants

9
Nuclear Fusion

• Suns energy comes from fusing of hydrogen to
  form helium
• Product has higher mass number than reactant

10
H H ? He n energy
11
Part II

• Mass Defect
• Binding Energy

12

Emc

• Mass Energy Equivalence
• Special Relativity

13
Rest Energy

• Matter at rest has rest energy, stored energy due
  to its mass.
• Energy is released when mass decreases in a
  nuclear reaction
• Mass and energy are equivalent
• Rest energy Emc2
• c is the speed of light not of the mass
• It takes energy to make mass

14
Mass Defect

• The nucleus of the atom is less massive than the
  total mass of its protons and neutrons
• Mass defect
• Dm(mass of constituent nucleons)
• -mass of the nucleus
• Note When calculating mass defect, keep all
  digits after decimal in the amus.

15
Binding Energy

• Energy required to separate a nucleus into its
  constituent nucleons
• Eb(Dm)c2
• Note
• 1 u 1.66054x10-27kg

16
Problem

• The mass of 12C is 12 u.
• Find the mass defect.
• Find the binding energy of its nucleus
• Find the binding energy per nucleon.
• b) 1.08x10-11 J c) 9 x 10 -13 J/nucleon

17
Energy of a Nuclear Reaction

• Conservation of mass and energy
• Endoergic(endothermic) Reaction Qlt0
• Massreactants energy? massproducts
• Exoergic (exothermic)Reaction Qgt0
• Massreactants ? massproducts energy

18
Threshold Energy

• Minimum kinetic energy required to start an
  endoergic reaction (activation energy)

19
Problem

• Calculate the energy released in the following
  fusion reaction
• 3 He 3 He ? 4 He 2 1 H
• 3.016029u 4.002603u 1.007825u
• Answer 2.06 x10 -12 J (or 12.9MeV)