Why lattice energy of lithium chloride is more exothermic than that of sodium chloride.
Think size of Li^+ vs Na^+.
bki
The lattice energy of an ionic compound is a measure of the strength of the electrostatic forces holding the ions together in the crystal lattice. It is an indication of the amount of energy required to separate one mole of a solid ionic compound into its gaseous ions.
In the case of lithium chloride (LiCl) and sodium chloride (NaCl), the lattice energy of LiCl is more exothermic than that of NaCl. This means that more energy is released when LiCl is formed from its constituent ions compared to NaCl.
To understand why this is the case, we need to consider a few factors:
1. Ionic Radius: The size of the ions involved plays a crucial role in determining lattice energy. Lithium (Li+) has a smaller ionic radius than sodium (Na+). Smaller ions have a higher charge density, which means that the positive charge is concentrated in a smaller volume. As a result, the electrostatic attraction between the oppositely charged ions in LiCl is stronger compared to NaCl.
2. Ion Charge: Both lithium and sodium ions have a +1 charge, so this factor does not contribute to the difference in lattice energy between LiCl and NaCl.
Considering these factors, we can conclude that the smaller ionic radius of lithium ions leads to a stronger electrostatic attraction between Li+ and Cl- ions in LiCl compared to Na+ and Cl- ions in NaCl. This stronger electrostatic attraction results in a more exothermic lattice energy for LiCl.
To actually calculate the magnitude of the lattice energy, one would need to use a mathematical model such as the Born-Haber cycle or the Kapustinskii equation, which take into account factors such as ion charges, sizes, and Madelung constants. Such calculations involve complex thermodynamic calculations and are beyond the scope of a simple explanation.