The lattice energy of Barium Chloride (BaCl2) is -2056 kJ/mol. This value represents the energy released when gaseous barium ions (Ba²⁺) and chloride ions (Cl⁻) combine to form one mole of solid BaCl2.
Understanding Lattice Energy
Lattice energy is a measure of the strength of the bonds in an ionic compound. It is specifically defined as the energy change that occurs when one mole of a solid ionic compound is formed from its constituent gaseous ions. A more negative (or larger in magnitude) lattice energy indicates a stronger attractive force between the ions in the crystal lattice, leading to a more stable compound.
This energetic value is crucial for understanding the stability and formation of ionic compounds and is often determined indirectly using the Born-Haber cycle. This cycle applies Hess's Law to relate the enthalpy of formation of an ionic compound to various other thermochemical steps, including:
- Enthalpy of sublimation of the metal
- Ionization energies of the metal
- Bond dissociation energy of the non-metal
- Electron affinity of the non-metal
Thermochemical Data for BaCl2 Formation
To understand the context of BaCl2 lattice energy, various thermochemical values related to its formation are considered. These values are typically used in a Born-Haber cycle calculation to determine or verify the lattice energy.
| Process | Energy Value (kJ/mol) | Description |
|---|---|---|
| Lattice Energy of BaCl2 | -2056 | Energy released when gaseous Ba²⁺ and Cl⁻ ions form solid BaCl2. |
| First Ionization Energy of Ba | 503 | Energy required to remove the first electron from gaseous Ba atom (Ba(g) ⟶ Ba⁺(g) + e⁻). |
| Second Ionization Energy of Ba | 965 | Energy required to remove the second electron from gaseous Ba⁺ ion (Ba⁺(g) ⟶ Ba²⁺(g) + e⁻). |
| Electron Affinity of Cl | -349 | Energy change when a gaseous Cl atom gains an electron to form a Cl⁻ ion (Cl(g) + e⁻ ⟶ Cl⁻(g)). |
| Bond Energy of Cl2 | 239 | Energy required to break the covalent bond in one mole of gaseous Cl2 (Cl2(g) ⟶ 2Cl(g)). |
| Enthalpy of Sublimation of Ba | 178 | Energy required to convert solid Ba to gaseous Ba atoms (Ba(s) ⟶ Ba(g)). |
| Standard Enthalpy of Formation of BaCl2 | Not provided directly | Energy change when one mole of BaCl2 is formed from its elements in their standard states (Ba(s) + Cl2(g) ⟶ BaCl2(s)). This value can be calculated using the Born-Haber cycle and the provided data. |
Importance of Lattice Energy
The magnitude of lattice energy significantly influences several properties of ionic compounds, including:
- Melting Point: Compounds with high (more negative) lattice energies typically have higher melting points because more energy is required to overcome the strong electrostatic forces holding the ions together in the solid lattice.
- Hardness: Stronger ionic bonds due to higher lattice energy often result in harder materials.
- Solubility: While other factors like hydration energy also play a role, very high lattice energies can sometimes make compounds less soluble in water, as a lot of energy is needed to break apart the lattice.
Understanding lattice energy is fundamental in predicting and explaining the physical and chemical properties of ionic substances in chemistry. For further reading on lattice energy and the Born-Haber cycle, you can explore resources on ionic bonding.
