 One is that the molar ratio of the constituents of an azeotrope is not generally the ratio of small integers.For example, the azeotrope formed by water and acetonitrile contains 2.253 moles ( or 9/4 with a relative error of just 2% ) of acetonitrile for each mole of water.A more compelling reason for believing that azeotropes are not compounds is, as discussed in the last section, that the composition of an azeotrope can be affected by pressure.