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Homework Help: Endothermic or Exothermic

  1. Oct 10, 2011 #1
    1. The problem statement, all variables and given/known data

    Label each of the following reactions as exothermic or endothermic ("exo" or "endo"), and according to whether work is done on or by the system, or no work is done at all ("on", "by" or "none")? Note that no "endo-on" cases appear here, as these are always thermodynamically unfavourable. There is no need to do any calculation, use chemical arguments to predict the sign of the enthalpy change.

    Pick from these > endo-by ,exo-none ,exo-by ,exo-on

    Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
    Cl2(aq) + 2 KBr(aq) → 2 KCl(aq) + Br2(aq)
    N2(l) → N2(g)
    NH3(g) + HCl(g) → NH4Cl(s)
    S(s) + 3/2 O2(g) → SO3(g)
    Last edited: Oct 10, 2011
  2. jcsd
  3. Oct 10, 2011 #2
    My attempt--- (are they right) ?
    Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) -- exo-on
    N2(l) → N2(g) -- exo by
    Cl2(aq) + 2 KBr(aq) → 2 KCl(aq) + Br2(aq) ---exo none
    NH3(g) + HCl(g) → NH4Cl(s) ---endo by
    S(s) + 3/2 O2(g) → SO3(g) ---endo by
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