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    I've calculated the enthalpy change of solution (dissolving) of an organic molecule in water to be +0.013 KJmol-1 in my lab experiment .. is this realistic? The wikipedia examples of enthalpy change of solution seem to be much much larger! But they're for inorganic/ionic compounds so I'm not sure if that's why.

    Thank you
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    (Original post by monkeyslut27)
    I've calculated the enthalpy change of solution (dissolving) of an organic molecule in water to be +0.013 KJmol-1 in my lab experiment .. is this realistic? The wikipedia examples of enthalpy change of solution seem to be much much larger! But they're for inorganic/ionic compounds so I'm not sure if that's why.

    Thank you
    ermm, solvation of ionic compound in water is always exothermic due to hydration enthalpy dominating over lattice enthalpy.

    but for organic compound, they shouldn't even be soluble in water in the first place, hence you tend to phase out aqueous and organic layer quite easily in labs. in the case they do, it tends to be the case of hydrogen bonding assisted or any other hydrophilic group that aids solvation. so it makes sense to have small value there.

    but hey, i can't really tell if you don't tell me what molecule you have got.
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    (Original post by shengoc)
    ermm, solvation of ionic compound in water is always exothermic due to hydration enthalpy dominating over lattice enthalpy.

    .
    This is not correct.

    Several ammonium salts, iodides and others have endothermic enthalpies of solution...
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    (Original post by charco)
    This is not correct.

    Several ammonium salts, iodides and others have endothermic enthalpies of solution...
    ah, those experiments that have flasks stuck on wooden plaque, classic! my bad.
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    (Original post by shengoc)
    ermm, solvation of ionic compound in water is always exothermic due to hydration enthalpy dominating over lattice enthalpy.

    but for organic compound, they shouldn't even be soluble in water in the first place, hence you tend to phase out aqueous and organic layer quite easily in labs. in the case they do, it tends to be the case of hydrogen bonding assisted or any other hydrophilic group that aids solvation. so it makes sense to have small value there.

    but hey, i can't really tell if you don't tell me what molecule you have got.
    oops, sorry I used potassium hyrdogen tartrate so it is an organic molecule and sparingly soluble although it does have an ionic bond (the potassium) and several polar regions due to the OH groups. so I understand why it's small... but POSITIVE? aahh i thought it should be exothermic for the reasons you say..

    thanks!
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    (Original post by shengoc)
    ah, those experiments that have flasks stuck on wooden plaque, classic! my bad.
    aaarrrghhhh!!!
    :angry:
 
 
 
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