Question

Calculate the lattice energy (kJ/mol) of the hypothetical ionic compound MX from the information given below.IE1(M) = 538 kJ/molM(s) => M(g) ΔHo = 74.4 kJ/molΔHof(MX) = -169.7 kJ/molX2(g) => 2X(g) ΔH = 157 kJEA (X) = -366 kJ/molIE1 (X) = 271 kJ/mol

Answer 1

Answer:

The correct answer is -494.6 kJ/mol

Explanation:

Find enclosed the Born Haber cycle for MX. The solid compound M (M(s)) is sublimated to M(g) and then it is ionizated to M⁺. The gaseous compound X₂(g) is first dissociated to its atoms in gaseous phase X(g) and then it is ionizated to give X⁻(g). Lattice energy (LE) is the energy required to form 1 mol of MX(s) from its ions in gaseous phase.

From the cycle, we have:

ΔHºf= ΔHsub + IE + ΔHdis + EA + LE

⇒LE= ΔHºf - ΔHsub - IE - 1/2 ΔHdis - EA

  LE= -169.7 kJ/mol - (74.4 kJ/mol) - (538 kJ/mol) - 1/2 (157 kJ/mol) - (-366 kJ/mol)

  LE= -494.6 kJ/mol