Now, when this guy is negative, when he's exothermic the bonds form are stronger than the bonds broken, so they're more stable. Now, when it's endothermic, when it's positive, the bonds form are weaker and less stable than the bonds that were broken. Now let's compare ideal and non ideal situations. Now, when we talk about ideal situations, we can graph Roth's law. And the Y axis is vapor pressure and the x axis is mole fraction. Now, we have two compounds here, compound A and compound B.