Which law states that the volume of a gas mixture is the sum of the pure component volumes?

• A. Amagat's Law
• B. Raoult's Law
• C. Boyle's Law
• D. Henry's Law

Answer: (A)

Gas mixtures follow a volume additivity principle: at a given temperature and pressure, the total volume of the mixture equals the sum of the volumes each pure component would occupy under the same conditions. This is Amagat's law. It means if you know how much volume each component would take alone at T and P, you can add those volumes together to get the mixture’s volume. In formula terms, V_mix = sum_i n_i * V_m,i(T,P), where V_m,i is the molar volume of component i at T and P. For ideal gases, all components have the same molar volume at a given T and P, so V_mix = n_total * V_m,ideal = n_total RT/P, which is consistent with the ideal gas law. Raoult's law concerns vapor pressures in solutions; Boyle's law relates P and V for a fixed amount of gas at constant temperature; Henry's law describes gas solubility in liquids.