How to identify deviation type from data: (1) Compare observed $P_{total}$ with Raoult's prediction — higher means positive deviation. (2) delta_H_{mix}: positive (endothermic) = positive deviation; negative (exothermic) = negative deviation. (3) delta_V_{mix}: positive (expansion) = positive deviation; negative (contraction) = negative deviation. (4) Similar molecules = ideal $\frac{benzene}{toluene}$. Disrupted H-bonds = positive $\frac{ethanol}{cyclohexane}$. New H-bonds formed = negative $\frac{chloroform}{acetone}$. Special case: two components that can form ion pairs or strong complexes show extreme negative deviation.