| Popis: |
For the thermochemical study of negative hydride-ion desorption from powdery saline hydride (MH n , n = 1 or 2) deposited on a molybdenum ribbon heater, both negative-ionic and electronic desorption currents from MH n were measured simultaneously as a function of sample temperature (ca. 700–800 K) by using a mass spectrometer, thereby yielding the new data that the desorption energy ( E − ) of H − and the work function φ) of the desorbing surface of MH n are, respectively, 536 and 318 kJ mol −1 for LiH, 728 and 492 kJ mol −1 for CaH 2 , and 937 and 702 kJ mol −1 for SrH 2 . Our energy cycle, consisting of the four indirect processes equivalent in reaction energy to the direct desorption of H − from MH n , indicates that the theoretical values of E − — φ are 227, 224 and 227 kJ mol −1 for LiH, CaH 2 and SrH 2 , respectively. They are in good agreement with our respective experimental values of 218, 236 and 235 kJ mol −1 within the experimental error of ca. ±5%. This agreement indicates that the desorption of H − from MH n is explained reasonably well by our simple model based on chemical thermodynamics. |
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