What is the relationship between total pressure and the partial pressures in a gas mixture?

What is the relationship between total pressure and the partial pressures in a gas mixture?

• A. The total pressure equals the sum of the partial pressures of all gases.
• B. Total pressure is the product of partial pressures.
• C. Partial pressures equal zero.
• D. Total pressure equals the maximum partial pressure.

Answer: (A)

Gases in a mixture each push on the container walls, and the total pressure is the combined effect of all those pushes. This is Dalton’s law: the total pressure equals the sum of the partial pressures of each gas. Each gas contributes a partial pressure based on how much of that gas is present (its mole fraction) at a given temperature and volume, and when you add all the partial pressures together you get the total pressure. For example, in air, nitrogen and oxygen together account for most of the pressure, with smaller contributions from argon and carbon dioxide; the partial pressures add up to about 1 atm at sea level. The other options don’t fit because multiplying partial pressures isn’t how pressures combine, partial pressures aren’t zero in a real mixture, and the total pressure isn’t just the largest single partial pressure.

Gases in a mixture each push on the container walls, and the total pressure is the combined effect of all those pushes. This is Dalton’s law: the total pressure equals the sum of the partial pressures of each gas. Each gas contributes a partial pressure based on how much of that gas is present (its mole fraction) at a given temperature and volume, and when you add all the partial pressures together you get the total pressure. For example, in air, nitrogen and oxygen together account for most of the pressure, with smaller contributions from argon and carbon dioxide; the partial pressures add up to about 1 atm at sea level.

The other options don’t fit because multiplying partial pressures isn’t how pressures combine, partial pressures aren’t zero in a real mixture, and the total pressure isn’t just the largest single partial pressure.