The total pressure of a gas mixture is the sum of the pressures that each component would exert if it were alone. This description corresponds to which law?

• A. Avogadro's Law
• B. Dalton's Law of Partial Pressures
• C. Charles' Law
• D. Boyle's Law

Answer: (C)

The statement describes Dalton's law of partial pressures. In a mixture of nonreacting ideal gases, each gas would exert the same pressure it would if alone at the same temperature and volume, and these pressures add up to give the total pressure: P_total = P1 + P2 + P3 + … . This works because each gas contributes to the total collisions with the container walls independently of the others, so the pressures simply sum. A gas’s partial pressure can also be expressed as P_i = y_i P_total, where y_i is its mole fraction. This additive behavior holds for ideal gases and explains why the total pressure reflects the sum of the individual components’ pressures. The other gas laws relate different variables (volume with temperature or with amount, or pressure with volume at fixed temperature) and do not describe this additive pressure behavior for a gas mixture.