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E=mc^2 states mass and energy are interchangeable but ?

  1. Jan 6, 2014 #1
    e=mc^2 states mass and energy are interchangeable but ??

    But daltons law of constabt mass is voilated as states that while a reaction the mass of product = mass of reactant
    any explainations?????
  2. jcsd
  3. Jan 6, 2014 #2


    Staff: Mentor

    I think you're mixing apples and oranges here. Einstein's E=mc^2 applies to nuclear reactions whereas Dalton's law applies specifically to chemical reactions.

    In a chemical reaction, electrons are interchanged, bonds are made, others are broken and energy is either given off or absorbed but no nuclear reactions are happening.
  4. Jan 6, 2014 #3

    ok thankyou so much jedishrfu
    my past 3 year doubt is now cleared thankyou so much
  5. Jan 6, 2014 #4
    In other words that change in mass is very small and hence negligible for molecules (not the same for nuclei-see link.).
  6. Jan 6, 2014 #5
    There is no violation because since mass and energy are equivalent, Dalton's Law is truly saying that the total of mass and energy remain constant (since they are equivalent), which it does.
  7. Jan 6, 2014 #6


    User Avatar

    Staff: Mentor

    You are wrong. E=mc2 is not about nuclear reactions, it is about mass and energy equivalence. Yes, it is most easily observable in nuclear reactions, but it doesn't mean it doesn't hold for other systems.

    In chemical reactions - strictly speaking - mass of products is NOT equal to mass of reactants when we take mass energy equivalence into consideration. However, the difference is many orders of magnitude lower than the accuracy with which we can weight substances involved, so for all practical purposes Dalton's law holds.
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