Talk:Mass excess

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I believe mass excess is the difference between the true mass M of an atom and the atomic number A (M - A), not the other way around! Thus, when the author gives the mass excess for uranium 236, he is wrong by a sign. Strangely, however, the mass excesses he provides for Kr-92, Ba-141, and a neutron ARE CORRECT, so he clearly ignored his own erroneous definition and did it the right way the second time. This inconsistency messes up his example calculation for the reaction's change in mass excess because the sign has been switched for reactants but not for products! Furthermore, when people compare the mass excesses of reactants and products in a reaction, most people find the difference in mass excess between the reactants and the products (mass excess of reactants - mass excess of products) , not the other way around. This backward expression is similar to the backward way he defines mass excess in the beginning, and should be changed. Thus, I think the overall difference in mass excess between the reactants and the products of his example should be:

0.045563 − ( − 0.1334366) = 0.1789996 u

not,

− 0.1334366 − ( − 0.045563) = − 0.0878736 u

Could someone verify this? If I'm not mistaken, please correct this. Firth m (talk) 01:24, 3 March 2008 (UTC)

[edit] I agree with the mistake

Yes, the original author's definition of mass excess is backwards and should be equal to the actual mass minus the atomic mass, which makes the label "mass excess" make much more sense. I also agree that the given mass excesses for ⁹²Kr, ¹⁴¹Ba, and the neutron are correct.

(see http://www.nndc.bnl.gov/masses/mass.mas03)

This should definitely be corrected in the future, as I looked to Wikipedia to learn the correct definition of mass excess and was erroneously turned down the wrong path in my calculation.

Annes72 (talk) 20:39, 17 April 2008 (UTC)annes72