Thermophysics of metal alkanoates VI. Heat capacities and thermodynamic properties of lithium n-pentanoate and n-heptanoate

Abstract

The adiabatic calorimetric study (at 5 to 350 K) of lithium n-pentanoate and n-heptanoate proved that solid-state transitions occur at Ttrs/K = 209.31 and 319.06 in the former salt, and at Ttrs/K = 317.08 in the latter one. Concerning n-pentanoate, the discontinuous (predominantly first-order) crystal-to-crystal transition at 209.31 K is followed almost immediately by a broad and diffused "hump" (with a maximum at 319.06 K), which stretches over a temperature range of about 110 K, and is apparently related to the occurrence of a gradual higher-order, possibly second-order) transformation. Concerning n-heptanoate, the nature and order of its single transition should be the same as suggested for the lower-temperature transformation of the shorter homolog. At the transition temperatures, the values of Cp,m/R, [Delta]trsSm/R, and [Delta]trsHm/R are 27.4, 0.39, and 80 K; and 32.9, 1.94, and 330.1 K, for the 209.31 K and 319.06 K transitions of lithium n-pentanoate, respectively; and 7800, 2.228, and 702.44 K for lithium n-heptanoate. Thermodynamic functions are tabulated at selected temperatures for both samples.