You are Here: Home >< Physics

# energy released

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
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
Attached Images

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.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
your full birthday is required
1. Oops, you need to agree to our Ts&Cs to register

Updated: June 22, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

### Who would you like to thank?

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.