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?
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.
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.
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??