1. Nuclear Chemistry Part II
Sections
Nuclear Chemistry Part II

2. Radioactive Decay Rates
Half-life – time it takes for ½ of the atoms in a sample of radioactive material to decay
Amount remaining = (Initial amount)(½)n
n = # of half-lives passed
Amount remaining = (Initial amount)(½)t/T
t is the elapsed time
T is the duration of the half-life
Practice Problems p

3. Nuclear Reactions & Energy
Energy released in chemical reactions is insignificant compared to the energy released in a nuclear reaction.
Any time a reaction involves an energy change, there is a mass change as well. (Even though this violates the Law of Conservation of Mass, the relationship between the two is expressed in Einstein’s equation, E =  mc2.)
Energy consumed/produced in chemical reactions is so small that the accompanying mass change is considered insignificant. (*not true for nuclear reactions)
Energy released from 1 kg of uranium is equivalent to energy released from 4 billion kg of coal.
Mass defect – difference in mass between nucleus and individual nucleons (plugged into E =  mc2 to account for huge release of energy)
Energy released when an atom’s nucleons bind together.
binding energy – energy required to break nuclei into individual nucleons
higher the binding energy  stronger the nucleons are held together  more stable nucleus
binding energy reaches peak around 60  elements with mass number of 60 are most stable

5. Fission – heavy atoms fragment into smaller atoms; always accompanied by very large release of energy
used to produce energy in power plants
chain reaction - neutrons released in one fission reaction used to initiate another, and another, and another . . .
An atomic bomb is an uncontrolled chain reaction.
Critical mass - fissionable material must contain a sufficient mass in order for a chain reaction to occur
subcritical mass – not enough to initiate chain reaction
supercritical mass – so much material that the reaction escalates violently (nuclear explosion)

7. Fusion – two or more light nuclei bond together to form a single more stable nucleus; capable of releasing large amounts of energy
occurs on the sun
hydrogen atoms fuse to form a helium atom
The lowest temperature capable of sustaining a fusion reaction is K!!!

9. Applications of Nuclear Rxns
Nuclear power plants – generation of electricity
Pros: reduces dependence on fossil fuels, no greenhouse gases (no global warming) produced, produces large amount of electricity from little fuel
Cons: storage of nuclear waste, possibility of nuclear failure (meltdown), target for terrorist attack, uranium a scarce resource
Nuclear medicine - radioisotopes used as radiotracers, PET scans, radiation therapy used to treat cancers
Military - atomic bombs, nuclear weapons

10. What Problems Are Associated with Nuclear Energy?
Proliferation Risks
Plutonium is a waste product of the fission of uranium and could be used to produce massive numbers of nuclear weapons.
Risk of Accident
Chernobyl, Three Mile Island
Can lead to death at site of explosion, but thousands’ health will be affected by radiation contamination
Environmental Degradation
The mining, refining & enrichment of uranium all pose environmental hazards.
Nuclear Waste
The waste products of the fission of uranium can remain radioactive for hundreds of thousands of years. How do we store this waste?