In a mixture of gases which do not react chemically together, the pressure of the individual gas is?

Analyze the question: It asks what we call the pressure exerted by each individual gas in a mixture of non-reacting gases.

Concept: Dalton's Law of Partial Pressures Dalton's law says that in a mixture of gases that do not react chemically, each gas behaves as if it alone occupied the whole container. The pressure each gas exerts on its own is called its partial pressure.

The total pressure is the sum of the partial pressures:

P_total = P₁ + P₂ + P₃ + ...

Check each option:

• A. Atmospheric pressure: This is the pressure exerted by the air around us. It is not the pressure of an individual gas in a mixture.
• B. Vapor pressure: This is the pressure of a vapor in equilibrium with its liquid or solid. It is not the general term here.
• C. Total pressure: This is the pressure of the whole mixture, not of one gas.
• D. Partial pressure: This is the pressure each gas in the mixture contributes. This matches the question.

Example: Air at 100 kPa contains about 21% oxygen. The partial pressure of oxygen is 0.21 × 100 = 21 kPa.

Exam tip: Remember "Dalton = Divide the pressure into Parts." Partial pressure goes with Dalton's law, and a question about "individual gas" in a "non-reacting mixture" almost always points to it.