The Entropy of Formic Acid. The Heat Capacity from 15 to 300°K. Heats of Fusion and Vaporization

Abstract

The heat capacity of solid and liquid formic acid has been measured from 15 to 300°K. The melting point is 281.40°K (0°C=273.10°K). The heat of fusion is 3031 cal. mole-1 and the heat of vaporization at 298.10°K is 4754 cal. mole-1. (1 mole=46.0260 grams.) The vapor pressure at 298.10°K is 4.31 cm of mercury. From the third law of thermodynamics and the calorimetric data the entropy has been calculated. To the value obtained from the calorimetric measurements an entropy of R/2 ln 2, due to the random orientation of hydrogen bonds in the solid which has been predicted by Pauling, has been added. This gives 31.51 cal. deg.-1 mole-1 for the entropy of the liquid at 298.10°K and 47.46 for the entropy of 46.0260 grams of gas, P=4.31 cm, in equilibrium with the liquid at 298.10°K. These are the values that should be used in thermodynamic calculations.

Vapor Pressure and Heat of Vaporization of Molecules That Associate in the Gas Phase

“…The vapours of formic and acetic acid are classical examples for strong dimerization, and generations of scientists have studied the effect of the dimers on their physicochemical properties 12,18 . Several complications lead to discordant results for all relevant experimental quantities (p-V m g -T data, vapour pressure, ∆ v H) -these are: (i) tendency for adsorption of the acid at the walls of the container 19 ; (ii) tendency to decompose to CO and H 2 O 20 ; (iii) water impurities 21,22 ; (iv) slow kinetics of equilibration between the monomers and the dimers 23 . In confirmation of the last point, Faubel and Kisters 24 found the evaporative flux carries strongly non-equilibrated mixture of monomers and dimers: what vaporizes from the surface at 252 K is a mixture of 70% monomers and 30% dimers, while the equilibrium fraction of dimers is approximately w 2 = 96% at this temperature; in addition, the average kinetic energy of the dimers is higher than that of the monomers, corresponding to an effective difference in temperature of 100-200 K 24 .…”

“…From our fitted value of ∆ v C 1 = −47.26 J/molK and the heat capacity of the liquid, C m l = 123.3 J/molK 36,37 , the capacity of the monomer follows, S1. We further simultaneously fit Eq (15) to vapour pressure data 21,22,39 falling in the range T = [-5, 120] °C and p = [1, 170] kPa, and Eq (8) to vaporization heat data 21,23,40 . The parameters p ꝋ = 5.692 kPa, ∆ v H ꝋ = 45.902 kJ/mol, and ∆ v C 1 = −39.3 J/molK are thus obtained (cf.…”

Piezoelectric Nylon‐11 Nanowire Arrays Grown by Template Wetting for Vibrational Energy Harvesting Applications

“…[52] Thus, in our fabrication process, a warm (~ 60 °C) formic acid solution of Nylon-11 was used to infiltrate the AAO template pores by the aid of capillary action. As the solution travelled through the pore channels, the viscosity increased due to rapid evaporation of formic acid (heat of vaporization = + 23.1 kJ mol -1 as compared to + 31.3 kJ mol -1 for acetone, + 40.66 kJ mol -1 for water), [53] forming microdroplets of Nylon-11 which appeared as a nano-particulate film on reaching the opposite template surface and on cooling thereafter ( Figure S2 in Supporting Information). The film thus obtained was loosely attached to the template surface and could be easily removed by mechanical polishing, leaving a nanowire-filled AAO template.…”

Nylon‐11 nanowires for triboelectric energy harvesting

“…For example, in this context, among possible good solvents of Nylon-11, formic acid can be chosen due to its rapid evaporation rate (heat of vaporization = +23.1 kJ mol −1 as compared to +31.3 kJ mol −1 for acetone, +40.66 kJ mol −1 for water). 43 The advantage of this evaporation-driven crystallization is that the temperature-induced chain mobility can be maintained throughout the process, resulting in much higher sample crystallinities ( Figure 5B). Figure 6 shows XRD patterns of various Nylon-11 film samples fabricated by both temperature-driven and evaporation-driven crystallization methods.…”

“…Therefore, the solvent should not only have good compatibility with the polymer material used, but it also needs to be relatively volatile (ie, having a high vapor pressure). For example, in this context, among possible good solvents of Nylon‐11, formic acid can be chosen due to its rapid evaporation rate (heat of vaporization = +23.1 kJ mol −1 as compared to +31.3 kJ mol −1 for acetone, +40.66 kJ mol −1 for water) 43 . The advantage of this evaporation‐driven crystallization is that the temperature‐induced chain mobility can be maintained throughout the process, resulting in much higher sample crystallinities (Figure 5B).…”