Ethanol has a density of 0.94 g mL⁻¹ in the solid state at −115 °C and 0.79 g mL⁻¹ in…
CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Ethanol has a density of 0.94 g mL⁻¹ in the solid state at −115 °C and 0.79 g mL⁻¹ in the liquid state at 25 °C. However, at 25 °C and 1 atm, 1 mol of ethanol vapor occupies more than 300 times the volume of 1 mol of the liquid. Which of the following best explains this observation?
(a) Intermolecular hydrogen bonding is maximized in the gas, forcing the molecules apart to occupy a very large volume.
(b) Because the molar mass of ethanol is constant, its density must drop dramatically when it boils, so the molar volume increases by a factor proportional to ρ1.
(c) In the solid and liquid, molecules are close together, but in the gas they are widely separated because intermolecular attractions become negligible at low pressure.
(d) The rigid crystal lattice collapses completely upon melting, creating internal voids that offset any increase in volume until the substance reaches the gas phase.