GATE 2021 MT – Question 35
A crystal’s vacancy concentration doubles when temperature increases from 27 °C to 127 °C. Vacancy-formation enthalpy is ______ kJ/mol (two decimal places). Given $R=8.314$ J mol$^{-1}$ K$^{-1}$.
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Correct answer: 6.85 to 7.00
Explanation
With unchanged prefactor, ln(c2/c1)=Hf/R(1/T1−1/T2). Using 300 and 400 K gives Hf=8.314ln2/(1/300−1/400)=6915.39 J/mol, or **6.92 kJ/mol**.