Intermolecular forces of non-ideal solution Question

[Monkeymaniac]

While I was reading the "Solutions" section of EK general chemistry book (page 72), I found something extremely vague and abstract.

While explaining Roult's law (vapor pressure is proportial to the fraction of molecules exposed to the surface of the solution), it said, "as we saw with heats of solution, if the solution is not ideal, the intermolecular forces between molecules will be changed. Either less energy or more energy will be required for molecules to break the intermoleuclar bonds and leavae the surface of the solution."

Here what is it referring to when it talks about a solution being non ideal? I couldn't find any references to the term in the book. Does anyone have a clue?

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[linkin06]

it can be nonideal in two situations. if the intermolecular forces are stronger, then the vapor pressure predicted by raoult's law will be less than expected and more energy is required to break the solutions apart. if the intermoleclar forces are weaker (as in repelling), then the vapor pressure will be larger than expected and less energy is needed to break them apart.

disclaimer: it's been a month since i took my mcat and studied, so this is from what i remember.