Help Me With Chemistry Ahhh

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  1. #1
    Shadow12345
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    Help Me With Chemistry Ahhh

    I have been doing chemistry for way too long I am about to shoot myself and 27 innocent immigrants.

    Here is the question:
    How is the energy of a quantum related to the frequency of emitted radiation
    Okay there are two possible answers, I suspect the first one is the one they are looking for but this could be another damn trick question

    1)
    anyway to find the energy of a photon you do the following:
    energy = h(planck's constant) * frequency
    2)
    the other possible answer is that the energy of a quantum never changes because a quantum is the smallest 'packet' of energy that matter can gain or lose.

    someone please tell me which they think is correct and why

  2. #2
    The Earth is not flat. Clyde's Avatar
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    "How is the energy of a quantum related to the frequency of emitted radiation"

    Are you sure thats the question?

    I'm not familiar with "a quantum" being anything, though you may be using terminology i'm not familiar with or you may be doing stuff i have not come across (which seems odd).

    If its a 'photon' not a 'quantum' it still doesn't seem to fit, because a photon IS the radiation emitted, but that could just be peculiar phrasing.

    If its a quantum system, then all you can say is that something within the system has lost energy (like an electron, in an atomic system), and that the loss in energy corresponds to the energy of the photon emitted (which in turn corresponds to the frequency via E=hf).
    Last edited by Clyde; 12-14-2002 at 03:33 PM.

  3. #3
    Shadow12345
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    a quantum is not a photon, however a photon (being the smallest 'particle of light') has exactly a quantum of energy, and yes I am sure that's how the question is phrased. I just put down the first thing I thought was correct from my original post, thank you for replying Clyde.

    EDIT: To put it differently a photon always has a quantum of energy, but depending on the beginning energy level of the electron and the energy level currently at can produce photons with different Joules of energy and I think that is what the question is getting at.

    I believe that is what 'h' is for, convert joules to quantums?

    6.626e-34 Joules * seconds / photon
    Last edited by Shadow12345; 12-14-2002 at 03:57 PM.

  4. #4
    The Earth is not flat. Clyde's Avatar
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    "a quantum is not a photon, however a photon (being the smallest 'particle of light') has exactly a quantum of energy"

    Ok, it is weird terminology, but ok, you call the amount of energy a photon has a 'quantum'.

    Well then the answer is E=hf as you said earlier.

    "I believe that is what 'h' is for, convert joules to quantums?"

    This statement doesn't seem to make sense; if you are saying that a 'quantum' is the amount of energy a photon has then that energy is already measured in joules, there is no conversion necessary.

    Planks constant (h) converts the frequency measured in hz into energy measured in joules, via E = hf.

    For radiation this value relates to the energy of a photon which is what you seem to calling 'a quantum'.

    "6.626e-34 Joules * seconds / photon"

    I don't quite understand what your doing here, f is measured in hz or S^-1 not seconds, so the energy per photon would be 6.626 *10^-34 * the frequency in hz or s^-1 of the radiation.

    "however a photon (being the smallest 'particle of light')"

    Thats not really true, photons are not exactly particles in the classical sense, they have wave-like and particle-like properties. Their 'size' is not a meaningfull concept, their energy on the other hand is.
    Last edited by Clyde; 12-14-2002 at 04:21 PM.

  5. #5
    Shadow12345
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    I don't quite understand what your doing here, f is measured in hz or S^-1 not seconds, so the energy per photon would be 6.626 *10^-24 * the frequency in hz or s^-1 of the radiation.
    that's because I forgot to include frequency

    energy = 6.626e-34 joules * second / photon (frequency)

    that should be more like it

    a quantum can mean both:
    The smallest amount of a physical quantity that can exist independently, especially a discrete quantity of electromagnetic radiation.
    This amount of energy regarded as a unit.


    " however a photon (being the smallest 'particle of light'"

    Thats not really true, photons are not exactly particles in the classical sense, they had wave-like and particle-like properties. Their 'size' is not a meaningfull concept, their energy on the other hand is.
    everything has wave and particle characteristics, even you

    represented by this equation
    lambda = h / mass * velocity

    so objects with huge masses have very small wavelengths.

    photons are pure energy and are considered to have no mass (they are gamma rays) a photon is the smallest 'unit' of light, it has a quantum of energy.

    This is all getting way too confusing, i'll ask my chemistry teacher next week and tell the results lol

    EDIT:
    here is the best definition I could find of joule

    a unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second

    EDIT1:
    One joule is approximately equal to 0.738 foot pounds.

    from www.dictionary.com
    Last edited by Shadow12345; 12-14-2002 at 04:27 PM.

  6. #6
    Just a Member ammar's Avatar
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    Talking

    Close this thread please.... No more chemistry.
    Just kidding
    none...

  7. #7
    The Earth is not flat. Clyde's Avatar
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    "energy = 6.626e-32 joules * second / photon (frequency)"

    what does second/photon mean?

    E = h f

    Energy, measured in joules (J) = planks constant, measured in Joule seconds (Js) * frequency, measured in hertz or 1/seconds (Hz or S^-1)

    "everything has wave and particle characteristics, even you"

    Well I don't actually have any observeable wavelike characteristics because my wavelength is too small. I no doubt have them, however I do not behave in a quantum way.

    "photons are pure energy and are considered to have no mass (they are gamma rays)"

    That's not quite true, photons are not considered to have REST mass, they do have a mass equivalent though, thats part of their particle like nature (mass relates to energy via E=mc^2)

    And they are not necessarily gamma rays, gamma is radiation at a specific wavelength (pretty small), but all electromagnetic radiation consists of photons; radiowaves, microwaves, visible light, infra red, xrays, gamma, etc.

    "A quantum can mean both:
    The smallest amount of a physical quantity that can exist independently, especially a discrete quantity of electromagnetic radiation.
    This amount of energy regarded as a unit. "

    Well I don't think its a term that is normally used, and the first definition seems a little odd because not all physical quantities are quantised into discrete packets.

    However your second definition seems to fit, a 'quantum' being the amount of energy a photon has, that energy is measured in joules, (joules being the unit used to measure energy -all energy)

    "This is all getting way too confusing, i'll ask my chemistry teacher next week and tell the results lol "

    Heh, i'm not confused, well, i find it somewhat odd that you are using a term i have never come across but that's just terminology, there is nothing wrong with the underlying principles.
    Last edited by Clyde; 12-14-2002 at 04:40 PM.

  8. #8
    Shadow12345
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    what does second/photon mean?
    uhh because that's the energy per photon

    That's not quite true, photons are not considered to have REST mass, they do have a mass equivalent though, thats part of their particle like nature (mass relates to energy via E=mc^2)
    are you agreeing with me or disagreeing with me or what

    And they are not necessarily gamma rays, gamma is radiation at a specific wavelength (pretty small), but all electromagnetic radiation consists of photons; radiowaves, microwaves, visible light, infra red, xrays, gamma, etc.
    good point

    Well I don't think its a term that is normally used, and the first definition seems a little odd because not all physical quantities are quantised into discrete packets.
    www.dictionary.com

    Heh, i'm not confused, well, i find it somewhat odd that you are using a term i have never come across but that's just terminology, there is nothing wrong with the underlying principles.
    which term haven't you come across?

  9. #9
    erstwhile
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    It would appear from your original question:
    How is the energy of a quantum related to the frequency of emitted radiation
    that 'quantum' is being used as a synonym for 'photon' which, although not unheard of, is unusual in this context. In this case, as Clyde has explained and you have suspected, your first answer is correct ie
    1)
    anyway to find the energy of a photon you do the following:
    energy = h(planck's constant) * frequency
    Consider also that you are specifically asked to relate 'energy to frequency' - which your first answer explicitly does.

  10. #10
    Shadow12345
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    Originally posted by Ken Fitlike

    Consider also that you are specifically asked to relate 'energy to frequency' - which your first answer explicitly does.
    Sounds good to me!!!!!

  11. #11
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    The answer they're looking for is either the equation E=hf or a written description of it.

    edit:

    h has the units J s and freq has the units s-1. Therefore E is measured in J, big suprise. It confused things a lot with the second/photon business.
    Last edited by crag2804; 12-15-2002 at 07:48 AM.

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