Chemistry - Thermochemistry Question with Solution | TestHub
The hydrogen bond between F- and CH3COOH is analysed by a Born-Haber cycle with the following data (in kJ/mol): lattice energy of NaF·CH3COOH, 740; enthalpy of vaporization of CH3COOH, 24; enthalpy of solution of NaF, 10; solvation energy of Na+(g), -410; solvation energy of F-, -389; enthalpy of formation of NaF·CH3COOH(s) from NaF(s) and CH3COOH(l), -30. Find the energy of the hydrogen bond between F- and CH3COOH in the gas phase (in kJ/mol).
Answer:
Solution:
Lattice enthalpy of NaF from ΔHsol = U - (solvation energies): UNaF = 10 + 410 + 389 = 809 kJ/mol. Route 1: NaF(s) + CH3COOH(l) → NaF·CH3COOH(s) (-30), then to Na+(g) + F-⋯HOOCCH3(g) (+740): net +710. Route 2: NaF(s) → Na+(g) + F-(g) (+809), CH3COOH(l) → (g) (+24), form H-bond (-x). Equate: 710 = 809 + 24 - x, so x = 123 kJ/mol. The answer is 0123.
