The effect of the water vapor pressure on the thermal dehydration of manganese(II) formate dihydrate was studied by means
of isothermal gravimetry under various water vapor pressure, ranging from 4.6 to 24.4 torr.
The kinetics of dehydration was described by a two-dimensional phase-boundary model,R2. The rate of dehydration decreased with increasing atmospheric water vapor pressure, but the Smith-Topley phenomenon was
not observed for the present dehydration. The activation energy and the frequency factor for the dehydration were 110–170
kJ·mol−1 and 1010–1016 cm·s−1, respectively. These values increased with increasing water vapor pressure, and were much larger than those reported for
the dehydration in vacuum.