Problem: Rubidium iodide has a lattice energy of -617 kJ/mol, while potassium bromide has a lattice energy of -671 kJ/mol.Why is the lattice energy of potassium bromide more exothermic than the lattice energy of rubidium iodide?

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FREE Expert Solution

We are asked to explain why the lattice energy of potassium bromide is more exothermic than the lattice energy of rubidium iodide.

Lattice energy represents the union of a gaseous cation and a gaseous anion in the formation of an ionic solid.


There are two main factors that contribute to the lattice energy of an ionic solid: 

  • the charge on the ions
    • as the charge of the ions increases, the lattice energy increases
  • the radius, or size, of the ions
    • as the size of the ions increases, the lattice energy decreases
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Problem Details

Rubidium iodide has a lattice energy of -617 kJ/mol, while potassium bromide has a lattice energy of -671 kJ/mol.

Why is the lattice energy of potassium bromide more exothermic than the lattice energy of rubidium iodide?