Thermodynamics of alkali alkanoates VII. Heat capacity and thermodynamic functions of potassium acetate from 4 to 585 K

Abstract

The heat capacity of potassium acetate was measured by equilibrium adiabatic calorimetry from near 4 K up to 350 K and by d.s.c. from 325 K through melting (solid to isotropic liquid) to 585 K. No transition or anomaly was observed below 300 K in the heat-capacity curve but four anomalies were observed at super-ambient temperatures including a broad and diffuse hump extending from 300 to 375 K. A bifurcated peak was observed between 375 and 436.5 K with peak temperatures at 411 and 425 K and with enthalpy increments (A,,,Ha of 41.7 and 22.8R. K and entropy increments (A&J of 0.097R and O.O5R, respectively. A peak believed to be of first order (solid-to-solid transformation) was observed at 474 K having A,HL and A,,.sP, of 194R. K and 0.407R. Finally, a solid-to-(isotropic) liquid transition occurred at 582 K having

Thermophysics of metal alkanoates. Heat capacities and thermodynamic properties of potassiumn-hexanoate from temperatures from 6 K to 600 K. VIII

“…Potassium butanoate showed two closely spaced but independent solid → solid intercrystalline transitions at temperatures between 100 K and 200 K. Lithium butanoate, however, showed a rather broad thermodynamic transformation, neither first nor second order, spanning a temperature range of over 100 K above T trs = 160 K. Interestingly, potassium acetate exhibits a broad and diffused hump extending between 300 K and 375 K. (1) Also, in potassium butanoate, (2) intercrystalline a The immediately preceding paper is that of reference 1. transformations were observed at temperatures (123.85 and 142.3) K much lower than (252.5 and 325) K of the hexanoate. The fact that such solid → solid transitions (s → s) occur in potassium hexanoate at higher temperatures than the corresponding transitions in potassium butanoate is consistent with the fact that temperature effects seem to be less prominent in longer chain members where the longer hydrocarbon tails are less susceptible to motional reorientation with increasing temperature.…”

“…The thermodynamic properties of potassium acetate, (1) potassium butanoate, (2) and lithium butanoate (3) have been reported earlier. Potassium butanoate showed two closely spaced but independent solid → solid intercrystalline transitions at temperatures between 100 K and 200 K. Lithium butanoate, however, showed a rather broad thermodynamic transformation, neither first nor second order, spanning a temperature range of over 100 K above T trs = 160 K. Interestingly, potassium acetate exhibits a broad and diffused hump extending between 300 K and 375 K. (1) Also, in potassium butanoate, (2) intercrystalline a The immediately preceding paper is that of reference 1. transformations were observed at temperatures (123.85 and 142.3) K much lower than (252.5 and 325) K of the hexanoate.…”

The cohesive energy of molten salts and its density

“…f From reference [28] for LiOH and reference [29] for RbOH. g With [H T À H 0 ] 1 from reference [30] for Li acetate, reference [31] for Na acetate, and reference [32] for K acetate.…”

NMR relaxation study of methyl groups in solids from low to high temperatures

“…where c ͑H͒ ϭ 1 3k ͑H͒ [39] and ⌰ 3 is the angle between R is (or q zz ) at separate sites. This angle for R is between protons in a methyl group is 120°.…”

“…[38] and the exponential temperature dependence of the correlation time (Eq. [39]) are responsible for a characteristic temperature dependence of T 1 . The T 1 values calculated from Eqs.…”