Thermal decomposition of solid sodium bicarbonate

The thermal decomposition of solid sodium bicarbonate has been studied in the temperature range 360–500 K over a range of partial pressures of carbon dioxide. The effect of water vapour has also been studied. Above 440 K the reaction follows contracting-cube kinetics with an activation energy of 32 kJ mol–1 and a frequency factor of 101 s–1. In this temperature range the presence of water or carbon dioxide has little effect on the kinetics. Below 390 K the reaction follows first-order kinetics. In nitrogen, the activation energy is ca. 64 kJ mol–1, the frequency factor is 105 s–1 and water vapour has little effect. High partial pressures of carbon dioxide increase the activation energy to ca. 130 kJ mol–1 and the frequency factor to 1013.5 s–1. The results of microscopic examination generally confirm the kinetics but show that at low temperatures in nitrogen and carbon dioxide the processes are different in detail.