When one mole of oxygen gas and two moles of hydrogen are combined in a sealed container at STP, what is true?

When one mole of oxygen gas (O₂) is combined with two moles of hydrogen gas (H₂) in a sealed container at standard temperature and pressure (STP), the correct statement is that the partial pressure of hydrogen is greater than the partial pressure of oxygen.

According to Dalton's Law of Partial Pressures, each gas in a mixture exerts a pressure proportional to its mole fraction in the total gas mixture. In this scenario, there are two moles of hydrogen gas for every one mole of oxygen gas, which gives hydrogen a higher mole fraction.

The total number of moles in the mixture is three (1 mole of O₂ + 2 moles of H₂). The mole fraction of hydrogen is therefore 2/3, and the mole fraction of oxygen is 1/3. Since partial pressure is directly related to the mole fraction in a given system at a constant temperature and volume, the partial pressure of the hydrogen gas will also be greater than that of the oxygen gas.

This scenario illustrates the basic principles of gas behavior under the conditions described, specifically how the stoichiometry of the gases involved affects their respective pressures in a mixture.