A student's solution reads: "Silicon dioxide has the formula

PHYSICS · Subjective · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Lattice dynamics and thermal properties of solids · Lattice dynamics and thermal properties of solids

Condensed Matter Physics, Ch Einstein, Debye and the heat capacity of solids

Problem

A student's solution reads: "Silicon dioxide has the formula SiO2\mathrm{SiO_2}, so a mole of it contains NAN_A vibrating units. Each unit carries 3N3N modes' worth of motion the way a single atom does, so CV=3R=24.94 J mol−1K−1C_V = 3R = 24.94\ \mathrm{J\,mol^{-1}K^{-1}}." Find the error in this reasoning, and give the correct classical (Dulong-Petit) molar heat capacity of SiO2\mathrm{SiO_2}, per mole of formula units.

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