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Physical change chemical change?

  1. Feb 21, 2006 #1
    In chemistry class they talk about physical change as something changing that is easily seen by the naked eye and chemical change as something more fundalmental that is something changing such as Na and Cl combining to form salt which is way different to Na or Cl.

    But what happens if you change the number of protons in an atom like a radioactive decay. It is not chemical and obviously not physical so what change is it?
  2. jcsd
  3. Feb 21, 2006 #2


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    Those definitions for physical and chemical changes are kind of vague and arbitrary, don't you think?

    I would call a reaction involving a change in the particles of a nucleus a nuclear reaction, which actually changes the *type* of the atoms involved, as opposed to a chemical reaction, in which the type of the atoms involved does not change, only their arrangement; they are recombined to form different substances or compounds. Particles in the atomic nuclei aren't affected. Chemical reactions only involve changes to the the electronic structure (meaning the structure of electrons) in the valence shells of the atoms involved...bonds are formed or broken, etc. etc. I'm being pretty general too.
  4. Feb 21, 2006 #3
    I think they are pretty vague also. I was thinking that we normally associate fundalmental changes as physics and chemistry as a subfield of phyics. But chemists try to look as though they are the important ones using the word physical for even smaller changes than chemical change. Nuclear change seems appropriate for a change in the structure of the nucleus but that is physics but they have already used up the word physical.
  5. Feb 21, 2006 #4
    That is most certainly a "physical" change. In addition, a change of atomic protons will change the properties of the atom itself, including it's potential "chemical" interaction, as the potential electron shell structure is likewise altered.
  6. Feb 21, 2006 #5
    The chemist has already used the word physicsal for changes that are apparent to the naked eye like a broken stick has physically changed compared to the original non broken stick
  7. Feb 21, 2006 #6
    The classic physical vs. chemical change lecture from HS Chem is not really a question of what is a physical change. Technically, things are being physically changed, moved around, etc on some level.

    Really what the teacher is asking is "does this form a new compound or not".
  8. Feb 21, 2006 #7


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    Also, another good way to think is, after the change can you put it back?

    If ice melts can you make it from water to ice again? Yeah, you freeze it.

    If you burn a match can you turn it into an unburned match again? No, you can't put all the smoke and heat back in.
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