Some chemists are investigating the composition of a gas mixture that has a total
pressure of 360 kilopascals. They find that the mixture contains three moles of hydrogen gas and one mole of
nitrogen gas. What is the partial pressure of the hydrogen gas in kilopascals?
The partial pressure is the pressure exerted by each individual gas in a mixture. Let’s consider a mixture of two gases, A and B. The partial pressure of gas A can be calculated by multiplying the mole fraction of
gas A by the total pressure of the mixture. The mole fraction is the amount of substance measured in moles divided by the total
amount of all of the substances in the mixture, also in moles.
The mixture in the question is composed of hydrogen gas and nitrogen gas. We want to know the partial pressure of the hydrogen gas in this mixture. So, we’ll first need to calculate the mole fraction of hydrogen gas. We are told in the question that the mixture contains three moles of hydrogen gas and
one mole of nitrogen gas for a total of four moles of gas. We can substitute the three moles of hydrogen gas and the four total moles into the
equation. Performing the calculation gives us a mole fraction of 0.75.
The question also tells us that the total pressure of the mixture is 360
kilopascals. We can substitute the mole fraction and the total pressure into the equation to solve
for the partial pressure of hydrogen gas. Performing the calculation gives us an answer of 270 kilopascals. This pressure is already in the specified unit.
Therefore, for the given mixture of gases, the partial pressure of the hydrogen gas,
PH2, equals 270 kilopascals.