NCERT · Class 12 · Chemistry · SolutionsState Raoult's law for solutions containing volatile liquid components and explain ideal and non-ideal solutions briefly.

According to Raoult's law for a solution of volatile liquids, the partial vapor pressure of each component of the solution is directly proportional to its mole fraction present in solution. For a binary solution containing two volatile liquids 1 and 2, the partial vapor pressure $p_1 = p_1^0 \cdot x_1$ and $p_2 = p_2^0 \cdot x_2$, where $p_1^0$ and $p_2^0$ are the vapor pressures of pure components 1 and 2 at the same temperature. Ideal solutions are those solutions which obey Raoult's law over the entire range of concentration. For an ideal solution, the enthalpy of mixing ($\Delta_{mix}H$) is zero and the volume of mixing ($\Delta_{mix}V$) is zero, meaning intermolecular solute-solvent forces are nearly equal to solute-solute and solvent-solvent forces (e.g., hexane and heptane). On the other hand, non-ideal solutions do not obey Raoult's law over the entire range of concentration. In such solutions, the enthalpy and volume of mixing are generally non-zero, and they show deviations—either positive or negative—from ideal behavior due to differences in intermolecular interactions.