Raoult's Law graphs

[unsung]

Can someone explain the Raoult's Law graphs to me. I don't understand the graphs of the deviations- i.e. when the curve is below the line, when the curve is above the line.

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[Quantum Chem]

When the vapor pressure lines of the individual substances the graph is showing negative deviation. When this occurs there is a greater interaction between the different liquids than there is with the same liquid. So in a mixture of X and Y, the X-Y interaction is greater than the X-X and Y-Y interaction.

Positive deviation is seen when the lines are above the theoretical line. This happens when X-X or Y-Y interactions are stronger than X-Y interactions. In ideal solutions the interactions are all equal: X-X = X-Y = Y-Y.

 

[CommSNTS]

http://www.chemguide.co.uk/physical/phaseeqia/idealpd.html

This site helped me understand it pretty well.

 

[gogopogo]

Wow do I love that site. Thanks a lot!

 

[Heyeon]

Thanks for the site. It really simplifies the concept!!

 

[unsung]

http://www.chemguide.co.uk/physical/phaseeqia/idealpd.html

This site helped me understand it pretty well.

I followed it up until they did the BP/vapor composition stuff. Think that stuff if necessary for MCAT? Good site, though.