Chemistry

Problem

Several familiar phenomena are governed by fundamental classes of chemical reactions. Consider the three processes described below. • Discharge of an alkaline battery (overall cell reaction):

Zn(s) + 2\,MnO_2(s) + 2\,OH^-(aq) \rightarrow Zn(OH)_2(s) + Mn_2O_3(s)

• Formation of calcium oxalate kidney stones:

Ca^{2+}(aq) + C_2O_4^{2-}(aq) \rightarrow CaC_2O_4(s)

• Atmospheric production of acid rain (overall):

SO_2(g) + H_2O(l) + \tfrac{1}{2}O_2(g) \rightarrow H_2SO_4(aq)

(a) For each process, identify the dominant reaction class (acid–base, redox, and/or precipitation). (b) For the battery discharge, use oxidation-number changes to justify the classification you assigned in part (a). Specify which species is oxidized and which is reduced. (c) For the kidney-stone formation, explain how lattice-energy and solubility considerations make the solid product more stable than the dissolved ions. (d) Acid-rain formation proceeds through several elementary steps. Describe how proton transfer and electron transfer are both involved across the sequence of steps, and explain why the overall process is commonly categorized as a redox reaction even though the final product is an acid.

Intuitive explanation

Each of these processes represents a different fundamental reaction class: the battery is a redox reaction where electrons transfer between species and energy is harnessed; kidney stone formation is a precipitation reaction driven by the insolubility of the product; and acid rain formation is an oxidation reaction where $SO_2$ is oxidized to a higher oxidation state. Recognizing which class governs each process tells you what thermodynamic or kinetic principles matter most—electron flow, solubility equilibria, or oxidation state changes.

Intuitive explanation

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