CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
At its melting point, naphthalene transitions from a molecular crystal to a liquid while remaining at essentially the same temperature.
Answer the following about the molar volume of naphthalene in its solid and liquid phases at the melting point (about 80 °C):
(a) Describe, at the particulate level, the positional arrangement and freedom of motion of naphthalene molecules in the crystalline solid immediately before melting and in the liquid immediately after melting.
(b) Using your description from part (a), explain—without performing numerical calculations—why 1 mol of liquid naphthalene occupies nearly the same macroscopic volume as 1 mol of solid naphthalene.
(c) Predict qualitatively how the molar volume of 1 mol of gaseous naphthalene at 1 atm would compare with the molar volumes you discussed in part (b). Justify your prediction in terms of the dominant types of intermolecular interactions and average intermolecular spacing in each phase.