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Half Reactions

  1. Jan 24, 2017 #1
    I do not have a clear concept about half-reactions...Can someone please give the half reactions for following reaction,
    Zn^0 + 2H^1 Cl^-1 -----> Zn^+2 Cl2^-1 + H2^0
    or Zn + HCl ----> ZnCl2 + H2
  2. jcsd
  3. Jan 24, 2017 #2


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    Gold Member

    "Half reaction" is used when you have to deal with oxidation/reduction reactions. Half reaction represents how electron is produced/consumed for reducing and oxidizing agent. So,
    Zn = Zn2+ + 2e-
    2HCl + 2e- = 2Cl- + H2
    Add both equation and you will see.
  4. Jan 24, 2017 #3
    Also one more thing...In the given equation, the oxidation state of H is changed...So would we say that H is being reduced or its whole compound HCl is being reduced???
  5. Jan 24, 2017 #4


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    Staff: Mentor

    In water Cl- is just a spectator, it is H+ that reacts.

    But in the gas phase, where only HCl is present I am ready to accept your statement as a correct. Pointing to an element in a compound and stating "this is what is being reduced/oxidized" is often questionable, as it is whole molecule/ion that undergoes the reaction. Yes, when we use oxidation numbers for redox reactions that how we think about the process, but oxidation numbers are just a accounting device designed for keeping track of electrons in the reaction. There is no property of an atom that we can measure to check its oxidation number.
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