Enthalpies of solution of Kbr, Ki, Kio3, and Kio4 in H2o

Abstract

Enthalpy of soluti on measureme nt s of four potassium salts in H20 were made in either an adiabatic or an iso pe ribol cal orimeter or both . The following summari zes the measured and recomme nd ed values: The value for KIO. has bee n corrected for the hydrol ys is of the pe ri odate ion. The .:lC " = -(82. 5 ± 4.3)J · mol -I ·K-1 for the unh ydrolysed reaction. For the reaction of KBr in H20 , .:l C " was measured as -(1 66.6 ± 7.2) ]-,nol -I·K -I in the temperature range 298 K to 3 19 K.Measure ments with the iso peribol calorimeter are also re ported for the e ndothermic reacti on of tri s(h ydrox ymeth yl)aminomethane, SRM 724a, in aqueous NaOH (0.05 mol·L -I).Compari sons of measurement s by different calorim eters on the same samples revea l unid e ntified calorimetri c eITors for e ndothermi c reactions which are greater than the imprec ision of the measurements.

The enthalpy of solution of SRM 1655 (KCl) in H2O

“…Gunn [4] s howed differences of as much as 35 J.mor l (0 .2%) in M ,o)n of samples with different ori gin s and drying procedures. A recent stud y [5] revea led systemati c errors of as much as 0. 7 perce nt in th e enthalp y of solution of KBr measured by three high-precision ca lori meters.…”

Systematic errors in an isoperibol solution calorimeter measured with standard reference reactions

“…In our earlier study on KBr [5] the isoperibol results of Efimov showed a puzzling curvature in the plot of the values for the enthalpy of solution of KBr versus concentration of the final solutions. It now appears that this was due to a comb ination of errors from thermal lags and inadequate stirring.…”

“…The vessel temperature was constantly rising throughout the experiment, and the mean temperature of the initial and final calibration periods differed from that of the reaction period by about 0.1 K or less (one exception was 0.3 K). The observed temperature 5 The results in section 4 indicate a sys temati c error estimated to be 0.06 percent du e to failure to me asure the e nergy equi va le nts over th e sam e tempe rature range as th e reacti o n. This would in crease th e mean valu e by 0.01 kj .mo!-I which would still he within th e experimental un ce rtaint y of th e valu e obtained from meas urements in th e adiabatic calorimete r.…”

“…However, in some laboratories [5,14], the jacket is maintained slightly below the final temperature of endothermic reactions (where electrical energy is not added). This was done to reduce the magnitude of the heat leak corrections, and the errors in such corrections.…”

“…Design criteria and possible sources of systematic errors in calorimeters have recently been discussed a priori in a series of papers by West, Churney, and Armstrong [1][2][3][4].1 They also suggest experimental tests to determine whether some systematic errors are likely to occur during calorimetric measurements. Recent work [5] indicated disagreement in results obtained by three calorimeters believed to be capable of measurements of highest accuracy and experimental imprecision of 0_1 percent or less. Two of these were isoperibol calorimeters of the same design used by different scienti sts at different locations; the values measured for the -Ce nt er for Thermodynamics and Molecu lar Science, Na ti onal Measurement Laboralory.…”