Two volatile liquids, A and B, form a perfectly ideal solution. If of A and of B are mixed at consta — Solutions and Colligative Properties Chemistry Question
Question
Two volatile liquids, A and B, form a perfectly ideal solution. If $0.5\text{ moles}$ of A and $0.5\text{ moles}$ of B are mixed at constant temperature and pressure, the theoretical entropy of mixing ($\Delta S_{mix}$) is strictly positive. For this exact ideal mixing process, what is the exact magnitude of the overall enthalpy of mixing ($\Delta H_{mix}$) in Joules?
💡 Solution & Explanation
By standard thermodynamic definition, an ideal solution features intermolecular forces (A-B) that are exactly identical to the pure state forces (A-A and B-B). Because breaking the old interactions costs the exact same amount of energy as is released upon forming the new interactions, the net enthalpy change ($\Delta H_{mix}$) is strictly $0\text{ J}$.