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# energy released Watch

1. Hi Guys,
for a reaction equation if you want to find out the energy released do you have to calculate the change in mass first and then use it in the equation E=mc^2 in order to find out the energy released?the question is on the attachment below. please have a look at it and let me know what you think thanks
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2. Yes, you need to calculate the difference in mass between the reactants and products. This mass difference can be converted into the energy released using E = mc^2.

Alternatively, as you are given the mass in terms of u, you can find the mass in terms of u and use the conversion 1 u = 931.5 MeV/c^2 to find the energy released in MeV.
3. (Original post by AlesanaWill)
Yes, you need to calculate the difference in mass between the reactants and products. This mass difference can be converted into the energy released using E = mc^2.

Alternatively, as you are given the mass in terms of u, you can find the mass in terms of u and use the conversion 1 u = 931.5 MeV/c^2 to find the energy released in MeV.
So basically should i convert that nuclear mass given in the question to MeV first and then takes it from there? Or is it not nessecarry ?
4. (Original post by Alen.m)
So basically should i convert that nuclear mass given in the question to MeV first and then takes it from there? Or is it not nessecarry ?
Convert all the masses into units of u and find the mass difference. The energy released is then 931.5 multiplied by this value, in MeV. (Assume the neutrino is massless.)
5. (Original post by AlesanaWill)
Convert all the masses into units of u and find the mass difference. The energy released is then 931.5 multiplied by this value, in MeV. (Assume the neutrino is massless.)
So masses has to be in the u unit all the time?
6. (Original post by Alen.m)
So masses has to be in the u unit all the time?
The conversion to kg in the definitions sheet doesn't have enough significant figures. see MS. http://filestore.aqa.org.uk/subjects...MS-JUN13.PDF#4

tbh I think that's a bit of a shady way of denying a mark but I guess that's how the examiner wants you to play it.

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