 Solution

ID: past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2025/4/a/ii/solution

ln K_{a} = - \frac{Δ _{r} G ^{\circ}}{RT} = - \frac{41133}{8.3145 ( 298 )} = - 16.6011, K_{a} = 6.17 \times 1 0^{- 8} .

The positive standard Gibbs energy of reaction means that dissociation is unfavourable when every thermodynamic activity equals one; it does not forbid partial dissociation. The corresponding

p K_{a} = - lo g_{10} K_{a}

is about

7.21

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