The decomposition of \(\mathrm{Ca}(\mathrm{OH})_{2}(s)\) into CaO(s) and \(\mathrm{H}_{2} \mathrm{O}(g)\) at constant pressure requires the addition of 109 kJ of heat per mole of Ca1OH22.
(a) Write a balanced thermochemical equation for the reaction.
(b) Draw an enthalpy diagram for the reaction.
Text Transcription:
Ca(OH)_2(s)
H_2O(g)
Step 1 of 5) Electrons for which the principal quantum number n is larger than the value of n for the electron of interest contribute 0 to the value of S. Electrons with the same value of n as the electron of interest contribute 0.35 to the value of S. Electrons that have principal quantum number n - 1 contribute 0.85, while those with even smaller values of n contribute 1.00. For example, consider fluorine, which has the ground-state electron configuration 1s2 2s2 2p5 . For a valence electron in fluorine, Slater’s rules tell us that S = 10.35 * 62 + 10.85 * 22 = 3.8. (Slater’s rules ignore the contribution of an electron to itself in screening; therefore, we consider only six n = 2 electrons, not all seven). Thus, Zeff = Z - S = 9 - 3.8 = 5.2+, a little lower than the simple estimate of 9 - 2 = 7+.values of Zeff estimated using the simple method outlined in the text, as well as those estimated with Slater’s rules, are plotted in Figure 7.5. While neither of these methods exactly replicates the values of Zeff obtained from more sophisticated calculations, both methods effectively capture the periodic variation in Zeff. While Slater’s approach is more accurate, the method outlined in the text does a reasonably good job of estimating Zeff despite its simplicity. For our purposes, therefore, we can assume that the screening constant S in Equation 7.1 is roughly equal to the number of core electrons.
