# What are positive and negative deviation with respect to ideal binary mixtures?

##### 1 Answer

Ideal solutions are such that

For **ideal binary mixtures**, let us suppose both components are at least somewhat volatile liquids.

When two liquids

- Liquid
#A# may prefer to interact more with liquid#B# than with liquid#A# (negative deviation). - Liquid
#A# may prefer to interact with liquid#A# more than with liquid#B# (positive deviation). - There may be no preference of
#A# or#B# to interact with either#A# or#B# over the other (ideal solution).

We can examine this relationship by considering the energies

**NEGATIVE DEVIATION LEADS TO VOLUME CONTRACTION**

With **negative deviation**:

#\mathbf(2epsilon_(AB) < epsilon_(A A) + epsilon_(BB))#

You can see the vapor pressure vs. mole fraction curve dip below the ideal/Raoult's Law lines, hence *negative* deviation.

Here, ** favorably** with liquid

Therefore, ** after** mixing, the most likely

*average distance*of molecule

**together than it would be from molecule**

*closer***the volume of the solution contracts after mixing**, relative to the ideal solution.

That means **difficult to make vaporize overall** because the molecules

**POSITIVE DEVIATION LEADS TO VOLUME EXPANSION**

On the other hand, with **positive deviation**:

#\mathbf(2epsilon_(AB) > epsilon_(A A) + epsilon_(BB))#

You can see the vapor pressure vs. mole fraction curve bulge above the ideal/Raoult's Law lines, hence *positive* deviation.

Here, ** poorly** with liquid

Therefore, ** after** mixing, the most likely

*average distance*of molecule

**away than it would be from molecule**

*farther***the volume of the solution expands after mixing**, relative to the ideal solution.

That means **easy to make vaporize overall** because the molecules