# Energy change in a nuclear reaction

## Homework Statement:

A fluorine - 18 nucleus can capture proton producing a neon - 19 nucleus as the product. The mass defect of fluorine - 18 and neon - 19 are 0.14712 u and 0.15398 u respectively. What is the energy change associated with this reaction?

## Relevant Equations:

E = mc^2
I got 6.5 MeV but I don't understand how to determine whether the energy is released or absorbed. My guess: the energy is absorbed because mass defect of neon is bigger?

Thanks

## Answers and Replies

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haruspex
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Homework Statement:: A fluorine - 18 nucleus can capture proton producing a neon - 19 nucleus as the product. The mass defect of fluorine - 18 and neon - 19 are 0.14712 u and 0.15398 u respectively. What is the energy change associated with this reaction?
Homework Equations:: E = mc^2

I got 6.5 MeV but I don't understand how to determine whether the energy is released or absorbed. My guess: the energy is absorbed because mass defect of neon is bigger?

Thanks
What is your understanding of how mass defect is defined?

What is your understanding of how mass defect is defined?
Difference between total mass of products and parents because some of the masses are converted to energy

haruspex
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Difference between total mass of products and parents because some of the masses are converted to energy
That's ambiguous because a difference is unsigned, and when given as the mass defect of an atom it is not in respect of an arbitrary disassemblage. Can you be more precise?

I think the more appropriate definition of mass defect is the total mass of proton and neutron minus mass of the nuclei

haruspex
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I think the more appropriate definition of mass defect is the total mass of proton and neutron minus mass of the nuclei
Right, so has the mass defect (of the whole system) increased or decreased? What does that mean about the change in total mass?

Right, so has the mass defect (of the whole system) increased or decreased? What does that mean about the change in total mass?
The mass defect of the system increases so the total mass also increases. This means that Ne has higher binding energy than F so some energy must be released to keep the energy conserved?

Thanks

haruspex
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The mass defect of the system increases so the total mass also increases.
A defect is a shortage. If I have a shortage of cash for something I want to buy and the shortage increases, do I have more cash or less?

A defect is a shortage. If I have a shortage of cash for something I want to buy and the shortage increases, do I have more cash or less?
Oh ok so since the shortage increases it means that mass of the product is less compared to mass of reactants so some of mass of reactants is converted to energy and released through the process

haruspex
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Oh ok so since the shortage increases it means that mass of the product is less compared to mass of reactants so some of mass of reactants is converted to energy and released through the process
Yes.

Thank you very much