Los procesos siguientes se analizaron en el capítulo 18 ,...

Los procesos siguientes se analizaron en el capítulo 18 , "Química ambiental". Estime si la entropía del sistema aumenta o disminuye durante cada proceso: (a) fotodisociación de $\mathrm{O}_2(\mathrm{~g})$; (b) formación de ozono a partir de moléculas de oxígeno y átomos de oxígeno; (c) difusión de los CFC en la estratosfera; (d) desalinización del agua por ósmosis inversa.

Key Concepts

Diffusion Processes

Diffusion is the process by which particles spread from regions of higher concentration to regions of lower concentration due to their random thermal motion. This spontaneous mixing increases the entropy of a system because it leads to a more uniform distribution of particles and energy, enhancing the number of disordered microstates available.

Entropy

Entropy is a thermodynamic quantity that measures the degree of disorder or randomness in a system. It is a central concept in the second law of thermodynamics, which states that for any spontaneous process, the overall entropy of the universe increases. In chemical processes, entropy is influenced by factors such as the number of particles, the phase of the matter, and the dispersal of energy, making it a key tool for predicting the spontaneity of reactions.

Photochemical Reactions

Photochemical reactions involve chemical changes induced by the absorption of light. In these processes, photons provide the energy needed to break chemical bonds, leading to the formation or alteration of molecular species. This input of energy can significantly affect the entropy of a system by increasing or redistributing the accessible energy states of the molecules involved.

Molecular Aggregation and Reaction Stoichiometry

Changes in molecular aggregation, such as the formation of new compounds from atoms or smaller molecules, affect the system's entropy. The transition from a greater number of individual, free particles to a more complex, aggregated molecular structure typically changes the number of microstates available, thereby influencing the entropy change associated with the reaction.

Reverse Osmosis and Membrane Separation

Reverse osmosis is a membrane separation process that uses external pressure to force a solvent through a semipermeable membrane, separating solutes from the solvent. Unlike natural osmosis, which tends to increase entropy by mixing substances, reverse osmosis creates a more ordered state by concentrating solutes, thereby decreasing the system's entropy locally. This process requires an input of energy to overcome the natural tendency of systems to become more disordered.

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