A materials engineer is investigating the feasibility of synthesizing new salt-based solid electrolytes. Four candidate reactions between pure elements are under consideration, each to be carried out at 500 °C and 5.0 atm in an inert atmosphere.
1. 2 Li(s) + Br₂(g) → 2 LiBr(s)
2. Sr(s) + S(s) → SrS(s)
3. Ba(s) + F₂(g) → BaF₂(s)
4. Al(s) + N₂(g) → 2⁄3 AlN(s)
The engineer must select the reaction that is projected to proceed most completely toward product formation under the stated conditions while minimizing input energy.
Rely on periodic trends in valence-electron configuration, ionization energy, electron affinity, and lattice energy to analyze the four reactions.
a) For each reaction, identify the charge and electron configuration of the cation and anion expected in the product.
b) Considering only periodic trends in first ionization energy and relevant electron affinities, order the four reactions from most to least favorable for initial electron transfer.
c) Explain how ionic charge and ionic radius together influence the lattice energy of each product, and predict which product’s lattice energy will be most negative (most exothermic).
d) Combine your reasoning from parts (b) and (c) to determine which reaction is most likely to be thermodynamically favorable under the given conditions. Support your answer with a brief, well-structured argument.