a gas law that states the total pressure of a combined mixture is equal to the sum of the individual pressures is

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

Answer: (C)

Gases in a mixture contribute separate pressures that add together. This is Dalton's Law of partial pressures: the total pressure of a gas mixture equals the sum of the partial pressures of each component gas. Each gas in the mixture exerts pressure as if it were alone in the container, and that partial pressure depends on how much of that gas is present at the given temperature and volume. Mathematically, P_total = P1 + P2 + P3, and since P_i = n_i RT/V, adding them gives P_total = (n1 + n2 + n3) RT/V. As long as the gases share the same temperature and volume, their pressures simply add.

Avogadro's law describes how volume relates to amount at fixed pressure and temperature; Boyle's law describes how pressure relates to volume at fixed amount and temperature; Charles' law relates volume to temperature at fixed pressure.