Difference Between Solvation Energy and Lattice Energy

Key Difference – Solvation Energy vs Lattice Energy
 

Solvation energy is the change in the Gibbs energy of a solvent when a solute is dissolved in that solvent. Lattice energy is either the amount of energy released during the formation of a lattice from ions or the amount of energy required to break down a lattice. The key difference between solvation energy and lattice energy is that solvation energy gives the change of enthalpy when dissolving a solute in a solvent whereas lattice energy gives the change of enthalpy when formation (or breakdown) of a lattice.

CONTENTS

1. Overview and Key Difference
2. What is Solvation Energy
3. What is Lattice Energy
4. Side by Side Comparison – Solvation Energy vs Lattice Energy in Tabular Form
5. Summary

What is Solvation Energy?

Solvation energy is the change in Gibbs energy when an ion or molecule is transferred from a vacuum (or the gas phase) to a solvent. Solvation is the interaction between a solvent and molecules or ions of a solute. The solute is the compound that is going to be dissolved in the solvent. Some solutes are composed of molecules whereas some contain ions.

The interaction between solvent and solute particles determine many of the properties of a solute. Ex: solubility, reactivity, colour, etc. During the process of solvation, solute particles are surrounded by solvent molecules forming solvation complexes. When the solvent involved in this solvation is water, the process is called hydration.

Different types of chemical bonds and interactions are formed during the solvation process; hydrogen bonds, ion-dipole interactions and Van der Waal forces. Complementary properties of solvent and solute determine the solubility of a solute in a solvent. For example, the polarity is a major factor that determines the solubility of a solute in a solvent. Polar solutes dissolve well in polar solvents. Nonpolar solutes dissolve well in nonpolar solvents. But the solubility of polar solutes in nonpolar solvents (and vice versa) is poor.

When it comes to thermodynamics, the solvation is possible (spontaneous) only if the Gibbs energy of the final solution is lower than the individual Gibbs energies of solvent and solute. Therefore, the Gibbs free energy should be a negative value (Gibbs free energy of the system should be decreased after the formation of the solution). The solvation includes different steps with different energies.

1. Formation of a cavity of solvent to make space for solutes. This is thermodynamically unfavourable because when the interactions between solvent molecule are decreased, and the entropy is decreased.
2. Separation of the solute particle from the bulk is also thermodynamically unfavourable. That is because the solute-solute interactions are decreased.
3. The solvent-solute interactions take place when solute enters the solvent cavity is thermodynamically favourable.

Solvation energy is also known as the enthalpy of solvation. It is useful to explain the dissolution of some lattices in solvents while some lattices do not. The change of enthalpy of solution is the difference between energies of releasing a solute from bulk and combining solute with solvent. If an ion has a negative value for the enthalpy change of solution, it indicates that the ion is more likely to dissolve in that solvent. A high positive value indicates that the ion is less likely to dissolve.

What is Lattice Energy?

Lattice energy is a measure of the energy contained in the crystal lattice of a compound, equal to the energy that would be released if the component ions were brought together from infinity. The lattice energy of a compound can also be defined as the amount of energy required to break down an ionic solid into its atoms in the gaseous phase.

 Ionic solids are very stable compounds due to the enthalpies of formation of ionic molecules along with the stability due to lattice energy of the solid structure. But the lattice energy cannot be measured experimentally. Therefore, a Born-Haber cycle is used to determine the lattice energy of ionic solids. There are several terms need to be understood before drawing a Born-Haber cycle.

1. Ionization energy – The amount of energy required to remove an electron from a neutral atom in the gaseous
2. Electron affinity – The amount of energy that is released when an electron is added to a neutral atom in the gaseous
3. Dissociation energy – The amount of energy required to break apart a compound into atoms or ions.
4. Sublimation energy – The amount of energy required to convert a solid into its vapour
5. The heat of formation – The change in energy when a compound is formed from its elements.
6. Hess’s law – A law which states that the overall change in the energy of a certain process can be determined by breaking the process into different steps.

The Born-Haber cycle can be given by the following equation.

Heat of formation = heat of atomization + Dissociation energy + sum of ionization energies + sum of electron affinities + lattice energy

Then the lattice energy of a compound can be obtained by rearranging this equation as follows.

Lattice energy = heat of formation – {heat of atomization + Dissociation energy + sum of ionization energies + sum of electron affinities}

What is the Difference Between Solvation Energy and Lattice Energy?

Summary – Solvation Energy vs Lattice Energy

Solvation energy is the change of enthalpy of a system during the solvation of a solute in a solvent. Lattice energy is the amount of energy released during the formation of a lattice or the amount of energy required to break down a lattice. The difference between solvation energy and lattice energy is that solvation energy gives the change of enthalpy when dissolving a solute in a solvent whereas lattice energy gives the change of enthalpy when formation (or breakdown) of a lattice.

Reference:

1.“Lattice Energy.” chem.purdue.edu. Available here 
2.International Union of Pure and Applied Chemistry. “Solvation energy.” IUPAC Gold Book – solvation energy. Available here 
3.“Solvation.” Wikipedia, Wikimedia Foundation, 5 Mar. 2018. Available here

Image Courtesy:

1.’Na+H2O’By Taxman (Public Domain) via Commons Wikimedia  
2.’Born-haber cycle LiF’By Jkwchui – Own work, (CC BY-SA 3.0) via Commons Wikimedia