The mole fraction of Frenkel defects in a NaCl crystal at 1000 K is — Solid State Chemistry Question

💡 Solution & Explanation

Mole fraction = $\sqrt{N_i / N_o} \cdot e^{-E/2RT}$. Assuming $N_i \approx 2 N_o$ for tetrahedral sites, $\sqrt{2} \approx 1.414$. $E = 73600$, $2RT = 4000$. $E/2RT = 18.4$. $e^{-18.4} \implies 2.3 \log y = -18.4 \implies \log y = -8 \implies y = 10^{-8}$. Total fraction = $1.414 \times 10^{-8}$. Therefore, correct answer is B.