Nuclear Fission - Calculations of Energy

In summary, the conversation discussed the calculation of energy released in a nuclear fission reaction and the confusion around the negative result. The solution was to remember that energy is conserved and to rearrange the equation to get a positive value for Q, indicating that energy was released in the reaction.
  • #1
Lissajoux
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Homework Statement



Example nuclear fission:

[tex]{}_{92}^{235}U+{}_{0}^{1}n \rightarrow {}_{38}^{90}Sr+{}_{54}^{163}Xe+10{}_{0}^{1}n+Q[/tex]

How much energy does such fission release?

Homework Equations



I'm given the values of [itex]M({}^{235}U), m_{n}, M({}^{90}Sr), M({}^{136}Xe)[/itex] but I've not listed them here.

The Attempt at a Solution



I thought that Q(energy) = energy in final state - energy in initial state. I.e. that:

[tex]Q={}_{38}^{90}Sr+{}_{54}^{163}Xe+9{}_{0}^{1}n -{}_{92}^{235}U[/tex]

But this gives me a negative answer, of around [itex]-0.15u[/itex]. I thought that it should be positive, unless this is just from how I've set out the equation and can just say it's positive. Done a few things similar to this, but still rather confused with getting the hang of it.
 
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  • #2
To get it straight just remember that you are conserving energy, so [tex]E_i = E_f[/tex]. Using this you get:

[tex]U+n = Sr+Xe+10n+Q[/tex]

[tex]Q = (U+n)-(Sr+Xe+10n)[/tex]

So, Q = (initial masses) - (final masses). Now it will be positive, meaning energy was released during this reaction. It all depends on where you put the Q in the reaction formula. It would be the other way around if Q was on the initial side (meaning it takes energy to perform the reaction).
 

1. What is nuclear fission?

Nuclear fission is a process in which the nucleus of an atom splits into smaller fragments, releasing a large amount of energy in the form of heat and radiation.

2. How is energy calculated in nuclear fission?

The energy released in nuclear fission can be calculated using the famous equation E=mc², where E is the energy released, m is the mass of the fissioned nucleus, and c is the speed of light.

3. What is the difference between nuclear fission and nuclear fusion?

Nuclear fusion is the process of combining two or more smaller nuclei to form a larger one, while nuclear fission is the process of splitting a larger nucleus into smaller ones. Both processes release a large amount of energy, but they differ in the elements involved and the energy released.

4. How does nuclear fission produce energy?

During nuclear fission, a small amount of mass is converted into a large amount of energy according to Einstein's famous equation E=mc². This energy is released in the form of heat and radiation, which can be harnessed for various purposes such as electricity generation.

5. What are some practical applications of nuclear fission?

Nuclear fission has several practical applications, including electricity generation in nuclear power plants, production of radioisotopes for medical and industrial purposes, and propulsion in nuclear submarines and spacecrafts.

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