When 1 g-equivalent of strong acid reacts with strong base, heat released is 13.5 kcal. When 1 g-equ — Thermodynamics and Thermochemistry Chemistry Question
Question
When 1 g-equivalent of strong acid reacts with strong base, heat released is 13.5 kcal. When 1 g-equivalent H2A is completely neutralized against strong base, 13 kcal heat is released. When 1 g-equivalent B(OH)2 is completely neutralized against strong acid, 10 kcal heat is released. What is the enthalpy change when 1 mole of H2A is completely neutralized by B(OH)2?
💡 Solution & Explanation
Neutralization of 1 mole of H2A by B(OH)2 involves 2 equivalents of each:<br>H2A + B(OH)2 → BA + 2$H_2O$.<br>The heat of neutralization for 1 equivalent of weak acid H2A with 1 equivalent of weak base B(OH)2 is:<br>ΔH_eq = ΔH_neut(SA/SB) + ΔH_diss(H2A) + ΔH_diss(B(OH)2)<br>We are given:<br>- ΔH_diss(H2A) per equivalent = 13.5 - 13.0 = +0.5 kcal/eq.<br>- ΔH_diss(B(OH)2) per equivalent = 13.5 - 10.0 = +3.5 kcal/eq.<br>Therefore, ΔH_eq = -13.5 + 0.5 + 3.5 = -9.5 kcal/eq.<br>For 2 equivalents (which corresponds to 1 mole of H2A reacting with 1 mole of B(OH)2):<br>ΔH_molar = 2 × (-9.5 kcal/eq) = -19 kcal/mol.