Entropy And Second Law

Question

Which of the following processes is associated with an increase in entropy of the system at constant temperature and pressure?

RankGuru · Accepted Answer

Entropy is a measure of disorder or randomness in a system. The Second Law of Thermodynamics states that spontaneous processes increase the entropy of the universe. When ammonium nitrate dissolves in water, the ionic lattice breaks apart into freely moving $NH_4^+$ and $NO_3^-$ ions in solution, dramatically increasing the disorder of the system — hence $\Delta S_{system} > 0$. Freezing of liquid water reduces molecular motion and produces a highly ordered crystal lattice, decreasing entropy. Condensation converts gaseous water (high entropy) to liquid (lower entropy), so entropy decreases. Formation of a crystal from a supersaturated solution is an ordering process that decreases entropy. This is directly covered in NCERT under entropy and spontaneity, noting that dissolution of ionic solids often involves large positive entropy changes. Plausibility check: the endothermic nature of NH$_4$NO$_3$ dissolution (it absorbs heat, making the container cold) confirms that entropy-driven thermodynamics governs the process despite an unfavorable enthalpy term.

Entropy And Second Law

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