In an insulated calorimeter, mixing of with of produces a temperature rise of . In an identical expe — Thermodynamics and Thermochemistry Chemistry Question
Question
In an insulated calorimeter, mixing $100 \text{ mL}$ of $1.0 \text{ M } HCl$ with $100 \text{ mL}$ of $1.0 \text{ M } NaOH$ produces a temperature rise of $5.7^\circ\text{C}$. In an identical experiment, $100 \text{ mL}$ of $2.0 \text{ M } CH_3COOH$ is mixed with $100 \text{ mL}$ of $1.0 \text{ M } NaOH$, producing a temperature rise of $5.6^\circ\text{C}$. If the standard enthalpy of neutralization of a strong acid and strong base is $-57.0 \text{ kJ mol}^{-1}$, what is the standard enthalpy of ionization of acetic acid?
💡 Solution & Explanation
Moles neutralized = $0.1 \text{ mol}$. Heat released in strong/strong = $0.1 \text{ mol} \times 57.0 \text{ kJ mol}^{-1} = 5.7 \text{ kJ}$. Calorimeter heat capacity $C = 5.7 \text{ kJ} / 5.7^\circ\text{C} = 1.0 \text{ kJ/}^\circ\text{C}$. Heat released in weak/strong = $C \times \Delta T = 1.0 \times 5.6 = 5.6 \text{ kJ}$. $\Delta H_{neut}(weak) = -56.0 \text{ kJ mol}^{-1}$. Enthalpy of ionization = $\Delta H_{neut}(weak) - \Delta H_{neut}(strong) = -56.0 - (-57.0) = +1.0 \text{ kJ mol}^{-1}$.