According to Dalton's Law of Partial Pressures, the partial pressure of a component in a gas mixture equals its mole fraction times the total pressure. This statement describes which principle?

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

Answer: (A)

In a mixture of non-reacting gases, each component contributes to the total pressure in proportion to how much of the mixture it represents. The mole fraction x_i is the fraction of all gas molecules that belong to that component, and its partial pressure P_i is x_i times the total pressure P_total. This relation, P_i = x_i P_total, is Dalton's Law of Partial Pressures, and it also implies that the sum of all partial pressures equals the total pressure, P_total = Σ P_i. For example, if a gas makes up 30% of the molecules and the total pressure is 2 atm, its partial pressure is 0.6 atm. The other laws don’t describe this distribution: Charles' Law links volume and temperature at constant pressure, Avogadro's Law links volume and amount at fixed T and P, and Henry's Law relates gas solubility in a liquid to partial pressure.