In Chemistry, the chapters students often fear the most usually turn out to be the most scoring ones. Thermodynamics and Ionic Equilibrium fall exactly
in this category. Both have limited formulas, clear concepts, and pattern-based questions. If prepared with understanding rather than memorisation, these two units alone can fetch 2–3 assured questions in JEE Main. Thermodynamics revolves around three core quantities: Enthalpy (ΔH), Entropy (ΔS) and Gibbs Free Energy (ΔG). Every reaction’s feasibility depends on their relationship. Remember the three golden rules:
- If ΔG is negative, the reaction is spontaneous.
- If ΔG is positive, the reaction is non-spontaneous.
- And the key equation is: ΔG = ΔH − TΔS.
This single relation explains whether heat and disorder together will drive a reaction forward. Topics like heat capacity, bond enthalpy and Hess’s Law are frequently tested. Instead of memorising steps, visualise Hess’s Law using energy-level diagrams. Many questions can be solved logically without recalling the entire process. The most common mistakes occur in sign convention and unit conversion, so always double-check them in the final step.
Now to Ionic Equilibrium — one of the most concept-rich and high-yield chapters in Physical Chemistry. It deals with equilibrium in aqueous solutions of electrolytes. The main focus areas include pH calculations, acid–base behaviour, buffer solutions, salt hydrolysis, common ion effect, and solubility equilibrium. Due to its vast syllabus, many students leave it incomplete, leading to unnecessary loss of marks.
Electrolytes are classified into strong (complete ionisation) and weak (partial ionisation). The behaviour of weak electrolytes is explained using Ostwald’s Dilution Law. Acid–base strength is defined by Ka and Kb, while pH = –log[H⁺] forms the backbone of this chapter.
Buffer solutions maintain stable pH and are solved using the Henderson–Hasselbalch equation. Salts formed from weak acids or bases undergo hydrolysis. The common ion effect suppresses ionisation, while solubility is explained using Ksp.
A simple but effective daily practice plan:
- Solve different types of pH problems
- Apply correct approximations
- Revise Ka, Kb, Kw and Ksp relations
- Practise buffer and salt solution numerical
With regular practice, Ionic Equilibrium becomes predictable and scoring.
Remember, success in Thermodynamics and Ionic Equilibrium does not come from rote learning but from understanding relationships. When ΔH, ΔS, ΔG align with pH, Ka, Kb and Ksp in your mind, these chapters turn into guaranteed scoring units, delivering both marks and confidence in the exam hall.
(Inputs from Nitin Vijay, Educator and Founder, Motion Education, Kota)
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