# Chap 3 Solns-5/E

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```12-35
12.30 This problem asks that we compute the number of Frenkel defects per cubic meter in silver chloride
at 350&deg;C. Solution of this problem is possible using Equation 12.2. However, we must first determine the value of
N, the number of lattice sites per cubic meter, which is possible using a modified form of Equation 4.2; thus
N =
=
N Aρ
AAg + ACl
(6.023 &times; 10 23 atoms/mol)(5.50 g/cm3 )(10 6 cm3 / m3)
107.87 g/mol + 35.45 g/mol
= 2.31 x 1028 lattice sites/m3
And, finally the value of Nfr is computed using Equation 12.2 as
⎛ Q ⎞
fr
⎟
N fr = N exp ⎜⎜−
⎟
2kT
⎝
⎠
⎡
⎤
1.1 eV
= (2.31 &times; 10 28 lattice sites/m3 ) exp ⎢⎥
-5
⎢⎣ (2)(8.62 &times; 10 eV/K)(350 + 273 K) ⎥⎦
= 8.24 x 1023 defects/m3
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```