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title: "The enthalpy diagram below illustrates a Born-Haber cycle for the formation of the ionic compound \\(\\text{MX(s)}\\) from its elements in their standard states at \\(298 \\text{ K}\\).  Which of the following correctly identifies the thermodynamic process for Step 5 and the lattice enthalpy (\\(\\Delta H^\\circ_{\\text{lattice}}\\)) for the reaction \\(\\text{M}^+\\text{(g)} + \\text{X}^-\\text{(g)} \\rightarrow \\text{MX(s)}\\)?"
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url: "https://nerd-notes.com/ubq/123913/"
date_modified: "2026-09-28T12:31:06+00:00"
---

# The enthalpy diagram below illustrates a Born-Haber cycle for the formation of the ionic compound \(\text{MX(s)}\) from its elements in their standard states at \(298 \text{ K}\).

Which of the following correctly identifies the thermodynamic process for Step 5 and the lattice enthalpy (\(\Delta H^\circ_{\text{lattice}}\)) for the reaction \(\text{M}^+\text{(g)} + \text{X}^-\text{(g)} \rightarrow \text{MX(s)}\)?

The enthalpy diagram below illustrates a Born-Haber cycle for the formation of the ionic compound \(\text{MX(s)}\) from its elements in their standard states at \(298 \text{ K}\).

Which of the following correctly identifies the thermodynamic process for Step 5 and the lattice enthalpy (\(\Delta H^\circ_{\text{lattice}}\)) for the reaction \(\text{M}^+\text{(g)} + \text{X}^-\text{(g)} \rightarrow \text{MX(s)}\)?

![An energy level diagram in grayscale. A single vertical upward arrow on the far left is labeled Enthalpy, H. Six horizontal solid black line segments represent energy levels. Level 0 at mid-height is labeled M(s) + 1/2 X2(g). A lower level below Level 0 is labeled MX(s); a solid downward arrow from Level 0 to this lower level is labeled Step 1: Delta H1 = -560 kJ/mol. Above Level 0, Level 1 is labeled M(g) + 1/2 X2(g); an upward arrow from Level 0 to Level 1 is labeled Step 2: Delta H2 = +90 kJ/mol. Above Level 1, Level 2 is labeled M+(g) + e- + 1/2 X2(g); an upward arrow from Level 1 to Level 2 is labeled Step 3: Delta H3 = +420 kJ/mol. Above Level 2, Level 3 is labeled M+(g) + e- + X(g); an upward arrow from Level 2 to Level 3 is labeled Step 4: Delta H4 = +80 kJ/mol. Just below Level 3, Level 4 is labeled M+(g) + X-(g); a downward arrow from Level 3 to Level 4 is labeled Step 5: Delta H5 = -330 kJ/mol. A dashed downward vertical arrow connects Level 4 directly to the lowest level MX(s) and is labeled Step 6: Delta H_lattice = ?. No other text, lines, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790598665-ZvWtCK.jpg)

- **A.** Step 5 is the ionization energy of \(\text{X(g)}\), and \(\Delta H^\circ_{\text{lattice}} = -300 \text{ kJ/mol}\).
- **B.** Step 5 is the electronegativity of \(\text{X(g)}\), and \(\Delta H^\circ_{\text{lattice}} = -820 \text{ kJ/mol}\).
- **C.** Step 5 is the electron affinity of \(\text{X(g)}\), and \(\Delta H^\circ_{\text{lattice}} = +820 \text{ kJ/mol}\).
- **D.** Step 5 is the electron affinity of \(\text{X(g)}\), and \(\Delta H^\circ_{\text{lattice}} = -820 \text{ kJ/mol}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123913/*