Partial Pressure

Properties of Partial Pressure

The partial pressure of gases is also affected by temperature, volume, and the number of moles of gas in a container.

• Pressure is directly proportional to temperature. Therefore, if you increase one of them, the other variable will also increase (Charles's Law).
• Pressure is inversely proportional to the volume. Increasing one variable will cause the other variable to decrease (Boyle's Law).
• Pressure is directly proportional to the number of moles of gas inside a container (Avogadro's law)

Dalton's Law of Partial Pressure

Dalton's law of partial pressure shows the relationship between partial pressures in a mixture. Being able to determine the partial pressure of gases is very useful in the analysis of mixtures.

The equation for Dalton's Law of Partial Pressure is simple. The total pressure of a mixture is equal to the partial pressure of gas A, gas B, and so on.

${\mathrm{P}}_{\mathrm{total}={\mathrm{P}}_{\mathrm{A}}+{\mathrm{P}}_{\mathrm{B}+...}}$

Fig.1-Mixing of gases and partial pressures

The partial pressure of gases can also be calculated using an equation that relates partial pressure to the total pressure and the number of moles.

$\mathrm{Partial}\mathrm{Pressure}\mathrm{of}\mathrm{a}\mathrm{gas}=\frac{n_{\mathrm{gas}}}{n_{\mathrm{total}}}\times {\mathrm{P}}_{\mathrm{total}}$

Where,

• P_total is the total pressure of a mixture
• n_gas is the number of moles of the individual gas
• n_total is the total number of moles of all gases in the mixture
• $\frac{n_{\mathrm{gas}}}{n_{\mathrm{total}}}$ is also known as the mole fraction.

Now, let's look at some examples to make things easier!

Henry's Law

Another law that relates to partial pressure is Henry's Law. Henry's Law proposes that when a gas is in contact with a liquid, it will dissolve proportionally to its partial pressure, assuming that no chemical reaction occurs between the solute and solvent.

The formula for Henry's Law is:

$C=kP$

Where,

• C = concentration of the dissolved gas
• K = Henry's constant that depends on the gas solvent.
• P = partial pressure of the gaseous solute above the solution.

So, can you apply Henry's Law to all equations involving a gas being and solution? No! Henry's Law is mostly applied to dilute solutions of gases that do not react with the solvent or dissociate in the solvent. For instance, you could apply Henry's Law to an equation between oxygen gas and water because no chemical reaction would happen, but not to an equation between HCl and water because hydrogen chloride dissociates into H⁺ and Cl^-.

$\mathrm{HCl}\left(\mathrm{g}\right)\stackrel{{\mathrm{H}}_2\mathrm{O}}{\to }{\mathrm{H}}_{\left(\mathrm{aq}\right)}^{+}+{\mathrm{Cl}}_{\left(\mathrm{aq}\right)}^{-}$

Importance of Partial Pressure

Partial pressure play a big role in various areas of life. For example, scuba divers are usually very familiar with partial pressure because their tank contains a mixture of gases. When divers decide to dive in deep waters where pressure is high, they need to know how changing partial pressures can affect their bodies. For example, If there are high levels of oxygen, oxygen toxicity may occur. Similarly, if there is too much nitrogen present, and it enters the bloodstream, it can cause nitrogen narcosis, characterized by decreased awareness and loss of consciousness. So, next time you go scuba diving, remember the importance of partial pressure!

Partial pressure also affects the growth of eukaryotic organisms like fungi! A very interesting study showed that when fungi were exposed to the high partial pressure of pure oxygen (10 atm), they stopped growing. But, when this pressure was quickly removed, they went back to growing as if nothing happened!

Examples of Partial Pressure

Practice makes perfect. So, let's solve more problems regarding partial pressure!

After reading this article, I hope you have become more familiar with the importance of partial pressures and how to apply this knowledge to situations involving partial pressures!