She ran to the professor. “I got 0.7887! Almost the same as the real one!”
Ramón shook his head. “Almost, but not exactly. The real density at 20°C is 0.7893. The difference? Thermal expansion, intermolecular gaps, defects. The theoretical density assumes a perfect, motionless crystal at absolute zero. It’s a map of a city that doesn’t exist. And yet,” he said, looking out the window, “without that map, we could never understand why real ethanol flows, why it mixes with water, why it burns.” densidad teorica del etanol
Elena spent the afternoon in the library. She found the atomic weights: C = 12.01, H = 1.008, O = 16.00. She added them: (2×12.01) + (6×1.008) + 16.00 = 46.068 g/mol. Then she searched for the molecular volume — estimated from X-ray diffraction of pure ethanol crystals at near-absolute zero. The theoretical volume per molecule came to roughly 97.0 ų per molecule (9.70 × 10⁻²³ cm³). She ran to the professor