1 minute read
Partial Pressures in Gases
PARTIAL PRESSURES IN GASES
When gases are together in a mixture, they each have a partial pressure. According to Dalton’s law (which is also called the Law of Partial Pressures), the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture.
Advertisement
According to the kinetic theory of gases (which will be further elaborated on soon), gases will diffuse in the container it is in in order to fill up the space it exists in and there is no force of attraction between the molecules. In other words, the different molecules in a mixture of gases are so far apart that they act independently from one another and do not interact. In an ideal gas, the collisions are between the gas and the container and not between each other so that the partial pressure isn’t affected by the other molecules in the gaseous chamber.
According to Dalton’s law, the total number of moles in a gaseous substance equals the sum of the moles of each gaseous molecule in a mixture. The mole ratio or Xi can be calculated by knowing the partial pressure of a certain gas and the total pressure of a certain mixture of gases. It describes the fraction of the mixture that is made up by a given gas. If oxygen, for example, takes up 4 atmospheres in a system consisting of 10 atmospheres, the mole ratio of oxygen is 4 divided by ten or 0.4. As you can imagine, the sum of the mole ratios of all the gases in a mixture must equal to one.
According to the ideal gas law, all gases behave exactly the same and their behavior is independent of repulsive and attractive forces. The only thing that is important in partial pressures is the number of molecules and not any other aspect of the nature of the gases themselves. In order to determine the partial pressure of a gas in a mixture, you need to know the molar mass of the molecule (the atomic mass) so that you can calculate the number of moles of the substance from the grams that might be given in an equation. This is why it is a good idea to have a periodic table that gives the atomic weight or atomic mass of the element.
