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    Hi, I'm learning about spontaneous reactions recently and I'm still a little confused with the definitions. Is it true that if something dissolves at a certain temperature, the dissolution reaction is spontaneous at that temperature. Can something dissolve non-spontaneously?

    Thanks in advance.
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    A spontaneous reaction is a reaction which is feasible/can happen. So yes, it would be spontaneous at that temperature
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    Oh I see. So all dissolution reactions are spontaneous reaction (delta G < 0)?
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    (Original post by alexkon)
    Oh I see. So all dissolution reactions are spontaneous reaction (delta G < 0)?
    Yes if something will dissolve the dG is negative (dG actually only indicates the equilibrium position between the dissolved and pure substance, for all dG except in the limit of infinitely disfavourable, there will be some dissolution of the solute). Because of the nature of the expression for dG (dG=dH-TdS), G changes with T as dissolution is highly favourable in terms of entropy. This is why things dissolve more readily at higher T.
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    (Original post by JMaydom)
    Yes if something will dissolve the dG is negative (dG actually only indicates the equilibrium position between the dissolved and pure substance, for all dG except in the limit of infinitely disfavourable, there will be some dissolution of the solute). Because of the nature of the expression for dG (dG=dH-TdS), G changes with T as dissolution is highly favourable in terms of entropy. This is why things dissolve more readily at higher T.
    Thanks for the explanation, that helps a lot.
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    (Original post by alexkon)
    Oh I see. So all dissolution reactions are spontaneous reaction (delta G < 0)?
    All reactions, both chemical and physical are spontaneous. If they weren't spontaneous they could not happen ...
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    (Original post by charco)
    All reactions, both chemical and physical are spontaneous. If they weren't spontaneous they could not happen ...
    but they are only spontaneous under certain conditions surely?

    admittedly, the difference between spontaneous and feasible has had me stumped recently. any thoughts?
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    (Original post by tangaroo)
    but they are only spontaneous under certain conditions surely?

    admittedly, the difference between spontaneous and feasible has had me stumped recently. any thoughts?
    True, but any reaction that actually happens MUST be spontaneous.

    There are only two criteria for reaction, thermodynamic and kinetic.

    A process could be spontaneous, but not happen because of kinetic control, BUT it cannot be non-spontaneous and still happen ...
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    (Original post by charco)
    True, but any reaction that actually happens MUST be spontaneous.

    There are only two criteria for reaction, thermodynamic and kinetic.

    A process could be spontaneous, but not happen because of kinetic control, BUT it cannot be non-spontaneous and still happen ...
    You can force a reaction by doing electrical work.
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    (Original post by JMaydom)
    You can force a reaction by doing electrical work.
    Then it becomes spontaneous ...
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    Hi again, I'm actually doing a practical to calculate dG for the dissolution reaction of potassium hydrogen tartrate. I'm almost certain that my results are accurate (by comparing to official results) and the values for dH and dS look reasonable. But I'm getting a positive dG for T = 298K even though there is obviously dissolution reaction going on at 298K. Why??
 
 
 
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