Non-ideal Deviations

Question

Positive deviation from Raoult's Law occurs when intermolecular interactions in mixture are:

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1. **Ideal Case**: Interactions $A\u2013A, B\u2013B$, and $A\u2013B$ are equally strong.
2. **Positive Deviation**: Occurs when the attractive forces between unlike molecules ($A\u2013B$) are **weaker** than those between like molecules ($A\u2013A$ or $B\u2013B$).
3. **Escaping Tendency**: Because $A$ and $B$ do not like each other as much, they escape into the vapor phase more easily than expected.
4. **Observation**: This results in a total vapor pressure that is **higher** than predicted by Raoult's Law ($P_{total} > x_A P_A^\circ + x_B P_B^\circ$).
5. **Example**: Ethanol and Cyclohexane. Cyclohexane breaks the hydrogen bonds in ethanol, increasing vapor pressure.

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Non-ideal Deviations

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