Heat of Hydration At least two physical chemistry laboratory texts (DANIELS,F.,et al., "Experimental Physical Chemistry," D. P., AND GARLAND, C. W., "Experiments in Physical Chemistry," McGrawMcGraw-Hill (6th ed.); SHOEMAKER, Hill (2nd ed.)), describe an experiment for measuring the differential and integral heat of solution of KNOa, an endothermic Drocess which m&es the exoerimental Drocedure emeciallv simole. There are several salts which have well defined ily,lrHte9 and for tihieh fhe.hn11 oi solution 111both spcciis is chothernlic. ' l l a ~ ,the experirnenr is e3iily mcditied u ~ r dcvrcnded so that studenta may obrniu the enrhnlpy 01 the rrwrion
.
anhydrous salt(cryst)
.
+ nHnO(liq) = hydrate(eryst)
an excellent illustration of the concept of enthalpy as a state function (Hess' Law). We find ILFe(CN)a and its trihydrate to be particularly suitsble because of the large enthalpy of solution of both species. WALTER DANNHAUSER
SUNY AT BUFFALO BUFPBLO.NEWYORK14214
Volume 48, Number 5, May 1971
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