Thermochemistry

Question

Write the thermochemical equation that would be used to represent the standard heat of formation of KBr(s).

AND Determine ∆H_f°

Answer 1

Use Born-Haber cycle to figure out enthalpy of formation KBr (s)

K (s) ------> K (g) ΔH_sublimation= 110.3 _kJ/mol

K (g) ------> K⁺ + e^- IE = 398 kJ/mol

1/2 Br₂ (l) ----> Br (g) E_atomization = 210 kJ/mol

Br (g) + e^- ------> Br^- E_{e affinity} = -349 kJ/mol

K⁺ + Br^- -------> KBr (s) E_lattice = -626 kJ/mol

K (s) + 1/2 Br₂ (l) -----> KBr (s) ∆H_f° = 110.3 + 398 + 210 + (-349) + (-626) = -256.7 kJ/mol