The variation of the ionic product of water () with temperature is thermodynamically determined. Whi — Ionic Equilibrium Chemistry Question
Question
The variation of the ionic product of water ($K_w$) with temperature is thermodynamically determined. Which of the following mathematical relations correctly correlates $K_w$ with absolute temperatures $T_1$ and $T_2$?
💡 Solution & Explanation
The auto-ionization of water is an endothermic process ($\Delta H^\circ > 0$). The temperature dependence of the equilibrium constant is rigorously given by the van 't Hoff equation: $\log \left(\frac{K_{w2}}{K_{w1}}\right) = \frac{\Delta H^\circ}{2.303R} \left(\frac{1}{T_1} - \frac{1}{T_2}\right) = \frac{\Delta H^\circ}{2.303R} \left(\frac{T_2 - T_1}{T_1 T_2}\right)$.