The key difference between bond enthalpy and lattice enthalpy is that the bond enthalpy is the amount of energy that is required to break down a chemical bond, whereas the lattice energy is the amount of energy that is required to form one mole of an ionic compound from the cations and anions in the gaseous state.
Both these terms describe energy exchange between a system and its surrounding. Bond enthalpy is the opposite of the lattice enthalpy. Bond enthalpy explains bond breaking while lattice enthalpy explains bond formation. This is why they are opposite phenomena to each other.
CONTENTS
1. Overview and Key Difference
2. What is Bond Enthalpy
3. What is Lattice Enthalpy
4. Side by Side Comparison – Bond Enthalpy vs Lattice Enthalpy in Tabular Form
5. Summary
What is Bond Enthalpy?
Bond enthalpy is the amount of energy that is required to break down a chemical bond. If we apply the standard definition here, it says that bond enthalpy is the enthalpy change when one mole of bonds are broken in a substance at 298 K. Since this term deals with bond breaking, we can name it as bond dissociation energy as well. Other synonyms include bond strength and average bond energy.
Figure 01: Bond Energies of Some Chemical Bonds
If the value of bond enthalpy is high, it means the bond is very strong and difficult to break down. Hence, it requires more energy to break down that particular bond. Typically, the units that we use for the determination of the value for bond enthalpy is kcal/mol (kilocalories per mole) or kJ/mol (kiloJoules per mole).
What is Lattice Enthalpy?
Lattice enthalpy is the amount of energy that is required to form one mole of an ionic compound under standard conditions using the cations and anions in the gaseous state. Since we are dealing with crystal lattices here, the term lattice enthalpy is used for crystal lattices; in other words, it is applied for solid compounds. It is a measure of the forces that bind the ions together (the cohesive forces).
Figure 02: A Lattice Structure
Generally, lattice energy is important in the determination of some physical properties, including solubility of crystals, hardness and volatility. Typically, lattice energy is a negative energy, but lattice enthalpy is a positive value. This is because the volume of a mole of the crystalline solid decreases when forming the lattice.
What is the Difference Between Bond Enthalpy and Lattice Enthalpy?
Bond enthalpy is the process opposite to lattice enthalpy since bond enthalpy deals with bond breaking while lattice enthalpy deals with bond forming. Hence, the key difference between bond enthalpy and lattice enthalpy is that bond enthalpy is the amount of energy that is required to break down a chemical bond whereas lattice energy is the amount of energy that is required to form one mole of an ionic compound from the cations and anions in the gaseous state. Bond enthalpy is the enthalpy change when one mole of bonds is broken in a substance at 298 K. Therefore, we can call it as bond dissociation enthalpy as well.
Summary – Bond Enthalpy vs Lattice Enthalpy
Bond enthalpy deals with bond breaking while lattice enthalpy deals with bond forming. Hence, the key difference between bond enthalpy and lattice enthalpy is that bond enthalpy is the amount of energy that is required to break down a chemical bond whereas lattice energy is the amount of energy that is required to form one mole of an ionic compound from the cations and anions in the gaseous state.
Reference:
1. Helmenstine, Anne Marie. “Bond Enthalpy Definition in Chemistry.” ThoughtCo, Aug. 8, 2019, Available here.
2. “Bond Energy.” Wikipedia, Wikimedia Foundation, 4 Nov. 2019, Available here.
3. “Lattice Energy.” Wikipedia, Wikimedia Foundation, 11 Nov. 2019, Available here.
Image Courtesy:
1. “Bond energies” By Chem540f09grp8 – Own work (Public Domain) via Commons Wikimedia
2. “Sodium-chloride-3D-ionic” By Benjah-bmm27 (talk · contribs) – Own work (Public Domain) via Commons Wikimedia