Answer:
Carbonates (CO3-2), phosphates (PO4-3) and sulfides (S-2) are insoluble.
The exceptions are the alkali metals and the ammonium ion.
Answer:
+60.54 kJ/mol
Explanation:
The enthalpy of formation of a compound is the sum of the enthalpies of the formation of its constituents and the bond of them. To form a compound, energy must be lost, so, they're negative.
For SF4, the enthalpy is formed by the energy of one S, two F, and 4 S-F bond (Hb):
H = - (278.8 + 4*79.0 + 4*Hb)
-775 = -(594.8 + 4Hb)
594.8 + 4Hb = 775
4Hb = 180.2
Hb = +45.05 kJ/mol
For SF6, the enthalpy is formed by the energy of one S, six F, and 6 S--F bonds (Hb):
H = -(278.8 + 6*79.0 + 6*Hb)
-1209 = -(752.8 + 6Hb)
752.8 + 6Hb = 1209
6Hb = 456.2
Hb = +76.03 kJ/mol
Thus, the energy of S--F bond must be the average of these two:
(45.05 + 76.03)/2 = +60.54 kJ/mol
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