A positive deviation from Raoult's law occurs when the intermolecular forces between unlike molecules (A–B) are weaker than those between like molecules (A–A and B–B). This causes the vapour pressure of each component to be higher than predicted by Raoult's law. When the positive deviation is large enough, the total vapour pressure curve shows a maximum, corresponding to a minimum in the boiling point vs. composition diagram. At this composition the solution boils at a temperature lower than either pure component, forming a minimum boiling azeotrope. Examples include ethanol–water and acetone–carbon disulphide systems. A maximum boiling azeotrope, by contrast, results from large negative deviations.