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?

Verified step by step guidance

1. Understand the concept of lattice energy: Lattice energy is the energy released when ions in the gaseous state form an ionic solid. It is influenced by the charges of the ions and the distance between them.
2. Consider the charges of the ions: Both rubidium iodide (RbI) and potassium bromide (KBr) involve ions with charges of +1 and -1, so the charge factor is the same for both compounds.
3. Examine the sizes of the ions: Rubidium (Rb) and iodide (I) ions are larger than potassium (K) and bromide (Br) ions. Larger ions result in a greater distance between the centers of the ions in the lattice.
4. Apply Coulomb's Law: The lattice energy is inversely proportional to the distance between the ions. Since RbI has larger ions, the distance is greater, resulting in a less exothermic lattice energy compared to KBr.
5. Conclude the comparison: The smaller size of K and Br ions in KBr leads to a stronger attraction between the ions, resulting in a more exothermic lattice energy compared to RbI.

Key Concepts

Lattice Energy

Lattice energy is the amount of energy released when gaseous ions combine to form an ionic solid. It is a measure of the strength of the forces between the ions in an ionic compound. A more negative lattice energy indicates a more stable ionic compound, as it reflects a greater release of energy upon formation.

Ionic Size and Charge

The size and charge of the ions involved in an ionic compound significantly influence lattice energy. Smaller ions can pack more closely together, leading to stronger electrostatic attractions and higher lattice energy. Additionally, ions with higher charges produce stronger interactions, resulting in more exothermic lattice energies.

Comparative Analysis of Ionic Compounds

When comparing ionic compounds like rubidium iodide and potassium bromide, it is essential to consider the specific ions involved. Potassium (K+) and bromide (Br-) ions are smaller and have higher charge density compared to rubidium (Rb+) and iodide (I-), which contributes to the greater lattice energy of potassium bromide, making it more exothermic than rubidium iodide.