12.4.2 Practice Megan Henderson

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12.4.2 Practice: A Pound of This and a Pound of That

Physical Science (S1744040)
Megan Henderson
Points possible: 50
Date: 01/7/2013
Fission

1.Uranium-235 decays naturally, by alpha decay. Write the balanced decay equation below. (5 points)

90231Th + 24He= 92235U

2.Uranium-235 has a half-life of about 700 million years. If 1 kg of U-235 is put on a shelf in a laboratory, how much of it will be left after 700 million years? (5 points)

There is barely any left, but there is 1/4kg.

3.Uranium-235 is a popular choice of fuel for nuclear reactors. But U-235 doesn't always fission the same way. Below are three ways it can split. Complete the nuclear equations so they balance. (6 points)

a)
b)
c)

4.Instead of allowing 1 kg of U-235 to decay naturally, imagine it is used as fuel in a nuclear reactor. It is bombarded with neutrons, causing it all to fission in a matter of days. After 1 kg of U-235 undergoes fission, the mass of the products is 8.4 x 10-4 kg less than the initial 1 kg. How much energy was produced by the fission of 1 kg of U-235? (Hint: Use Einstein's equation, E = mc2, where E is energy in Joules, m is mass in kilograms, and c is the speed of light, 3 x 108 m/s.) (8 points)

The Uranium loses 8.4 x 10^-4kg. Plug this into the equation E = mc^2 and that is the answer.

Fusion
5.The fusion of two hydrogen isotopes is shown below. Complete the nuclear equation so it balances. (5 points)

It would be about 2H (or H-2) and 3H (or H-3) isotope


6.If 1 kg of fuel is used in the above fusion reaction, the resulting helium has a mass of 0.993 kg. In other words, 0.007 kg of mass is converted to energy. How much energy is produced by the fusion of 1 kg of hydrogen? (Hint: Use Einstein's equation, E = mc2, where E is energy in Joules, m is mass in kilograms, and c is the speed of light, 3 x 108 m/s.) (6 points)

E--> mc2
E--> 0.007 x (3x108)2
E--> 6.3 x 1014J


Alternative Energy
7.Hydrogen fuel cells combine hydrogen and oxygen to produce water and energy. Assume 1 kg of fuel is used, and the mass of the water produced is 1.10 x 10-11 kg. How much energy is produced by this fuel cell? (Hint: Use E = mc2.) (7 points)

When you use 1kg of hydrogen to produce 16 kwh of energy.


Comparison
8.Complete the following table and questions. (8 points)
Reaction Mass "Lost" Energy Produced

Fission= of 1 kg of U-235
Fusion= of 1 kg of hydrogen
Fuel cell= with 1 kg of hydrogen and oxygen


Which type of reaction "loses" the most mass?

a fusion reaction loses the most mass.

Which type of reaction produces the most energy? Why?

A redox reaction produces the most energy.