What happens when you dissolve liquids with liquids?

Answer 1

When one combines two liquids there are two thermodynamic properties to consider. First, in no particular order, is Entropy and second is Enthalpy. The entropy of mixing is always positive. Entropy is the measure of disorder and when two liquids are mixed this allows for more states to be occupied providing position entropy. If one considered entropy alone then all liquids would mix, which isn't true(see Oil and Water). So one must also consider enthalpic effects. These effects deal with the type of intermolecular forces that each liquid can take part in. For instance, when one mixes methanol and water heat is evolved. This is because the methanol-water interaction is more favorable than the methanol-methanol interaction. As a result heat is given off because the molecules have reached a lower potential energy well. Also a neat thing to see is that when mixing two liquids that give off heat when mixed one will notice a decrease in the total volume of the solution. This is because of the favorable interactions literally pulling the molecules closer to each other.