Just done an experiment where you dissolve benzoic acid in water at different temperatures and different volumes of water.(adsbygoogle = window.adsbygoogle || []).push({});

From the van't hoff equation you then plot a graph of ln(solubility) against 1/Temp which produces a straight line with gradient -ΔH/RT from which you get the enthalpy change.

(vant hoff equation): lnk = -ΔH/RT + constant

The first question was:

why isnt it necessary to express solubility in mol/l despite ΔH beight evaluated in J/mol?

I answered with:

It isn’t necessary to convert solubility into mol/l because it’s the difference in solubility that’s important. Therefore plotting solubility with either units will always produce a line of the same gradient but with different Y intercept (the intercept being insignificant)

Is that ok?

The second question im stuck on is:

Why is it that solubility, S, may be used instead of the equilibrium constant, K, in the van't hoff equation?

I would guess they are proportional to each other or something?

would really appreciate any help

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# Homework Help: Determination of enthalpy of solution (solubility/temp stuff)

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