Amagat's Law states that the volume of a gas mixture is the sum of the pure component volumes. Which statement best reflects this?

• A. Amagat's law
• B. Dalton's law
• C. Raoult's law
• D. Gibbs-Duhem relation

Answer: (A)

This question hinges on the idea that gas volumes in a mixture add up. Amagat's law says that at the same temperature and pressure, the volume of a gas mixture equals the sum of the volumes that the pure components would occupy in that same conditions, i.e., the volumes are additive through partial molar volumes: V = sum_i n_i * V̄_i. For ideal gases, every component has the same molar volume at a given T and P, so the total volume reduces to V = n_total RT/P, consistent with the ideal gas law. This additive-volume view is the essence of Amagat's law. The other laws describe different properties: Dalton's law concerns partial pressures summing to total pressure, Raoult's law addresses vapor pressures in solutions, and the Gibbs–Duhem relation ties together changes in chemical potentials with composition.