Lr. Watson et al., HIGH-TEMPERATURE MASS-SPECTROMETRIC STUDIES OF THE BOND-ENERGIES OF GAS-PHASE ZNO, NIO, AND CUO, Journal of physical chemistry, 97(21), 1993, pp. 5577-5580
The equilibria Ni(g) + 1/2O2(g) reversible NiO(g), Cu(g) +1/2O2(g) rev
ersible CuO(g), CuO(g) + Ni(g) reversible Cu(g) + NiO(g), and Zn(g) 1/2O2(g) reversible ZnO(g) were studied by high temperature mass spect
rometry with a position-sensitive ion detection system. Except for ZnO
(g), all gaseous species in these equilibria were observed. The DELTA(
f)H-degrees-298(II,III)[NiO(g)] and D-degrees-0(II,III)[NiO(g)] determ
ined reinforce literature values within experimental error. Values obt
ained for DELTA(f)H-degrees-298[CuO(g)] and D-degrees-0[CuO(g)] have a
large uncertainty associated with them, perhaps due to lack of equili
brium. Moreover, second and third law heats are not in agreement. ZnO(
g) was not observed; however, by evaluating the sensitivity of the ins
trument, a lower limit for the standard enthalpy of formation for ZnO(
g) was determined: DELTA(f)H-degrees-298[ZnO(g)] greater-than-or-equal
-to 151 kJ/mol. From this value an upper limit for the dissociation en
ergy of ZnO is determined: D-degrees-0[ZnO(g)] less-than-or-equal-to 2
26 kJ/mol (less-than-or-equal-to 2.3 eV). This bond energy is 48 kJ/mo
l (0.5eV) lower than the upper limit obtained from a previous thermoch
emical study but is in agreement with a more recent determination base
d on a study of threshold for an ion-neutral reaction.7