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E=mc² machine

  1. Sep 28, 2010 #1
    Hope this theoretical question isnt too stupid, just my physics teacher couldnt give me a satisfying answer and im only 14. (english is also not my mothertongue, pls excuse grammatical failures)

    So what if there was some sort of machine, that would just convert mass into energy after e=mc².

    If you were to feed this machine first with 1 kg of CO², you'd get 9 GJ.

    If you were then to feed this machine with the aquivalent of C and O needed to produce 1kg of CO², but seperatly, you'd still get out the 9 GJ.

    But what happend with the theoretical chemical Energy C and O has?

    Does it maybe get lost when C and O becomes plasma thus releasing the energy held by the angle of the electron pairs to eachother?

    So, doesnt that also mean, that no such machine could exist, without having to heat up the mass to a very high point?
  2. jcsd
  3. Sep 28, 2010 #2
    The "empirical" law of baryon number conservation (the sum of protons plus neutrons) prevents conversion of 1 Kg of CO2 (~500 g of protons, ~500 g of neutrons, ~0.25 g of electrons) into pure energy. Excluding considering nuclear binding energies, 1 kG of protons and 0.5 g of electrons would have the least mass that conserves baryon number.

    Bob S
  4. Sep 28, 2010 #3
    There is no machine you can use, but there is a physical processs called Annihilation. When a particle and its antiparticle (electron positron for example) 'collide' the result is a total conversion of MATTER to energy. It should be noted that it's matter you're thinking of, not mass... mass is present as a function of energy-momentum too.

    If you take a molecule of helium, and anti-helium, the result is a total conversion from matter to energy, including all of the binding energies: chemical, molecular, atomic. Annihilation is the only means that I know of which conceivably gives 100% efficiency for conversion.
  5. Sep 28, 2010 #4
    Such a machine would indeed be impossible when taking into regard some advanced physics.

    However, let's assume for now we could make such a machine. It is true that to make CO2 from the seperate components takes some energy. This energy can be found by precisly weighing C and O seperatly and then weighing the combination: CO2. You would find that the CO2 is ever so slight heavier than the weight of a C and two O's added! The difference in weight is minute, a lot smaller than 1%. But precisly that weight is the energy (through E-mc^2) that it takes to bind the C and O atoms. It is called the binding energy. So feeding the machine CO2 would make it produce a little more energy.

    Good question!
  6. Sep 28, 2010 #5
    Huh? You have this reversed.

    The C + O -> CO2 reaction is exothermic (gives off energy). This is normal every-day combustion. It is, in fact, a very common reaction. You see it when charcoal burns in your barbecue grill. The heat of the charcoal comes from this reaction.

    C and O want to combine because the combination has LESS mass, NOT MORE. CO2 has less mass than C and 2 O.

    From: http://en.wikipedia.org/wiki/Binding_energy

    (bold is mine)
  7. Sep 28, 2010 #6
    You're right, my bad.
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