The Bends - Chemistry LibreTexts

The Solubility as a Function of Pressure

English chemist William Henry discovered that as the pressure increases, the solubility of a gas increases. Henry's Law is then:

\[ C =k P_{gas} \]

where

• C=solubility of a gas in a solvent at a specific temperature,
• Pgas is the partial pressure of the gas, and
• k is Henry's Law Constant

In the case of The Bends:

• If a diver goes deeper and deeper into the water, more nitrogen builds up in the bloodstream and other tissues.
• Following Henry's Law; as the pressure increases, the solubility of nitrogen in the diver's bloodstream increases.
• As a result, nitrogen from the compressed air stays in the bloodstream and other tissues
• However, since the diver is in a highy-pressurized environment, the excess N2 can only be relieved when the diver ascends to levels with lower external pressure
• Ideally, this should happen during the diver's gradual rise to the surface
• Unfortunately, sometimes, the diver ascends too quickly, resulting in the rapid formation of bubbles, which interfers with nerves, blood and lymphatic vessels and leads to excruciating joint pain and clotting.

Example \(\PageIndex{1}\):

Determine Henry's Law Constant, k, with the information that the aqueous solubility of N2 at 10 degrees Celsius is 11.5 mL N2 / L and 1 atm.

\( k= \dfrac {11.5 mL N_{2}/ L}{\ 1 atm} \)

Now if the Pgas of N2 increases to 5 atm:

\[ P_{N2}=\dfrac {C}{\dfrac {11.5 mL N_{2}/ L}{\ 1 atm}} \]

\[ 5 atm=\dfrac {C}{\dfrac {11.5 mL N_{2}/ L}{\ 1 atm}} \]

Solve for C: C= 57.5 mL N2 /L

Therefore, both examples show that as the the pressure increases from 1 atm to 5 atm, the solubility of the N2 gas increases from 11.5 to 57.5 mL N2 / L. This supports Henry's Law.