Lattice Energy — Predicted 2026
AI-Predicted Question Angles for UPSC 2026
Comparative Analysis of Lattice Energy Trends
highNEET frequently tests the ability to compare lattice energies of different ionic compounds. This often involves series where either the cation or anion changes, allowing students to apply the rules of ionic charge and size. For example, questions comparing $LiF$, $NaF$, $KF$ (varying cation size) or $NaCl$, $MgCl_2$, $AlCl_3$ (varying cation charge) are highly probable. Students need to understand that charge is the dominant factor, followed by size. Expect MCQs asking to arrange compounds in increasing or decreasing order of lattice energy.
Born-Haber Cycle Calculation (Numerical)
mediumWhile not as frequent as conceptual questions, numerical problems involving the Born-Haber cycle are a staple. These questions require students to calculate lattice energy given other enthalpy terms (sublimation, ionization, dissociation, electron affinity, enthalpy of formation) or to find one of the enthalpy terms given the lattice energy. The complexity often lies in ensuring correct stoichiometry (e.g., for $MgCl_2$, two ionization energies and two electron affinities are needed) and proper sign conventions for exothermic/endothermic processes. A well-structured step-by-step solution is key to avoiding errors.
Conceptual Understanding and Misconceptions
highQuestions testing the fundamental definition of lattice energy, its nature (exothermic for formation), and why it cannot be directly measured are common. Distinguishing lattice energy from other thermodynamic terms like enthalpy of formation, bond dissociation energy, or hydration energy is a frequent trap. Questions might also probe the relationship between lattice energy and physical properties (melting point, solubility), asking students to explain observed trends based on lattice energy principles. Understanding the 'why' behind the trends is as important as knowing the trends themselves.