Question 6.7: calculating the energy change in the Formation of an Ionic c...
Calculating the Energy Change in the Formation of an Ionic Compound
Calculate the net energy change in kilojoules per mole of KF(s) that takes place on formation of KF(s) from the elements: K(</span><span class="fontstyle2">s)</span><span class="fontstyle3"> </span><span class="fontstyle4">+ </span><span class="fontstyle0">1/</span><span class="fontstyle0">2 F_{2} </span><span class="fontstyle0">(</span><span class="fontstyle2">g)</span> <span class="fontstyle4">→ </span><span class="fontstyle0">KF(</span><span class="fontstyle2">s)<span class="fontstyle0">. The following information is needed:
Heat of sublimation for K(s) = 89.2 kJ/mol E_{ea} for F(g)= -328 kJ/mol
Bond dissociation energy for F_{2}(g) = 158 kJ/mol E_{i} for K(g) = 418.8 kJ/mol
Electrostatic interactions in KF(s) = -821 kJ/mol
STRATEGY
Write a chemical reaction for each step in the process of forming the ionic solid KF and draw a Born–Haber cycle similar to Figure 6.7. The sum of the energy changes for each step should give the energy change for the overall reaction.

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