E=mc^2

[Sisyphus]

So 1g of matter is convertible to 25,000 kwh of electricity at 100% efficiency, regardless of what type of matter it is? So a fusion reactor that would convert hydrogen to helium would only deplete 1g of mass per 25,000kwh generated? So how would you figure out how much mass is lost in the conversion? Is this also explained by E=MC^2 or does that require attention to the internal structure of the atoms in question?

 

That would be 25,000,000 kwh, not 25,000. And yes, you need to know the masses of H and He to figure out how much you'll be going through.