GCEChemistryChemical Bonding2020

The lattice energy of an ionic compound can be calculated using a Born-Haber cycle. Given the following data for the formation of sodium chloride: enthalpy of formation = $-411$ kJ/mol, atomization enthalpy of Na = $+108$ kJ/mol, atomization enthalpy of Cl = $+122$ kJ/mol, first ionization energy of Na = $+496$ kJ/mol, electron affinity of Cl = $-349$ kJ/mol. The lattice energy of NaCl is

A$-788$ kJ/molCORRECT
B$+788$ kJ/mol
C$-698$ kJ/mol
D$+411$ kJ/mol
AI
Toaster Teacher
Why the answer is A, and why the others tempt you.
Using Hess's law: Lattice energy = Enthalpy of formation − (atomization of Na + atomization of Cl + ionization energy of Na + electron affinity of Cl) = −411 − (108 + 122 + 496 + (−349)) = −411 − (377) = −788 kJ/mol. The negative value confirms energy is released when the ionic lattice is formed, consistent with lattice formation being exothermic.
Want this in Pidgin, Yoruba, Igbo or Hausa? Sign up free →

Practice more Chemistry questions

GCE Chemistry has thousands more questions like this — with Worked answers on every one.

Start practicing free →See all Chemistry questions