When atoms of the hypothetical element X are placed together, they rapidly undergo reaction to form the X2 molecule:
X(g) + X(g) → X2(g)
a. Would you predict that this reaction is exothermic or endothermic? Explain.
b. Is the bond energy of X2 a positive or a negative quantity? Why?
c. Suppose ∆H for the reaction is 500 kJ/mol. Estimate the bond energy of the X2 molecule.
d. Another hypothetical molecular compound, Y2(g), has a bond energy of 750 kJ/mol, and the molecular compound XY(g) has a bond energy of 1500 kJ/mol. Using bond-energy information, calculate
H for the following reaction.
X2(g) + Y2(g) → 2XY(g)
e. Given the following information, as well as the information previously presented, predict whether or not the hypothetical ionic compound AX is likely to form. In this compound, A forms the A+ cation, and X forms the X anion. Be sure to justify your answer.
Reaction: A(g) + 1/2X2(g) → AX(s)
The first ionization energy of A(g) is 400 kJ/mol.
The electron affinity of X(g) is 525 kJ/mol.
The lattice energy of AX(s) is 100 kJ/mol.
f. If you predicted that no ionic compound would form from the reaction in part e, what minimum amount of AX(s) lattice energy might lead to compound formation?