Lithium iodide has a lattice energy of -7.3 * 10^2 kJ/mol and a heat of hydration of -793 kJ/mol. Find the heat of solution for lithium iodide and determine how much heat is evolved or absorbed when 15.0 g of lithium iodide completely dissolves in water.

Name: Chemistry: A Molecular Approach
Author: Tro
ISBN: 9780137832217

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Identify the given values: Lattice energy of lithium iodide (LiI) is -730 kJ/mol and the heat of hydration is -793 kJ/mol.

Use the formula for the heat of solution: \( \Delta H_{solution} = \Delta H_{hydration} - \Delta H_{lattice} \).

Substitute the given values into the formula: \( \Delta H_{solution} = -793 \text{ kJ/mol} - (-730 \text{ kJ/mol}) \).

Calculate the molar mass of lithium iodide (LiI) by adding the atomic masses of lithium (Li) and iodine (I).

Convert 15.0 g of LiI to moles using its molar mass, then multiply the moles by the heat of solution to find the total heat evolved or absorbed.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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 requires more energy to break the ionic bonds. In this case, lithium iodide has a lattice energy of -730 kJ/mol, indicating the energy released during the formation of the solid from its gaseous ions.

Heat of Hydration

The heat of hydration is the energy change that occurs when ions are surrounded by water molecules and solvated. It is typically exothermic, meaning it releases energy, as water molecules stabilize the ions. For lithium iodide, the heat of hydration is -793 kJ/mol, indicating that a significant amount of energy is released when lithium and iodide ions dissolve in water, contributing to the overall energy change during the dissolution process.

Heat of Solution

The heat of solution is the overall energy change when a solute dissolves in a solvent, calculated as the sum of the lattice energy and the heat of hydration. It can be either exothermic (releasing heat) or endothermic (absorbing heat) depending on the magnitudes of these two energies. For lithium iodide, the heat of solution can be determined by adding the lattice energy and the heat of hydration, allowing us to assess whether the dissolution process is heat-releasing or heat-absorbing.

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