The Sidney Young equation is used to correct values of this quantity based on changes in pressure. Various values of this quantity form the two axes of a Dühring plot. Mole fractions for the substance with a smaller value of this quantity define the axes of a McCabe–Thiele plot. By reducing pressure, (-5[1])a rotovap lowers the value of this quantity (10[2])for the solvent (10[1])in the flask. Negative azeotropes have a higher value of this quantity than either of their components, (10[1])and hence cannot be separated by simple distillation. (10[1])The ebullioscopic (10[1])constant times molality times van ’t Hoff factor calculates a colligative property known as this quantity’s namesake “elevation.” For 10 points, name this quantity of a substance at which vapor pressure equals surrounding pressure, causing it to vaporize. ■END■ (10[1])