Question

Thermodynamics of potassium nitrate dissolving in water experiment post-lab questions: What does the sign of the delta G tell you about the dissolution process for this experiment? Is the dissolution process spontaneous at all temperature? If not at what temperature does this spontaneity change?

Answer 1

A dissolution process generally increases randomness of a system. So dissolution of KNO3 in water is a spontaneous process means ΔS= +ve

the relation between Ksp and ΔS is as follow.

-RTlnKsp = ΔG .................(1)

note that

as temperature increases, solubility also increases

so solubility product will also increase.

Generally spontaneous process is governed only by sign of entropy.

But here ΔG if negative also indicate spontaneous reaction.

Now observe the equation 1

At higher temperature Ksp will increase and will cause

increase in negative value of ΔG (so actually G decreases)

so it can be said that at higher temperature ΔG will be

more negative and process will be more spontaneous.

ΔG = ΔH - TΔS

The transition spontaneous to non spontaneous occurs at equillibrium, where

ΔG = 0

so ΔH = TΔS

T= ΔH/ ΔS

If you know values of  ΔH/ ΔS you can find temperature at which transition occur.