Chemistry in action: It is commonly known that resurfacing while scuba diving is a risky action. However the reasoning behind why is often mistaken; resurfacing too quickly causes dissolved nitrogen in the bloodstream to form bubbles under the skin due to the sudden rapid change in pressure; this is a condition commonly known as “the bends”. An example of what the bends looks like is pictured above on the left. Coincidentally, such a condition is a concrete example of chemistry in action; more specifically a concept known as LeChâtelier’s Principle, which states that any stress exerted upon a chemical equilibrium causes the equilibrium to shift in the direction that relieves the stress. In this case, the equilibrium in question is the simple conversion between aqueous and gaseous nitrogen (N2) in the bloodstream.
The equilibrium is written as follows: N2 (aq) <-> N2 (g)
As a scuba diver descends under the ocean’s surface, pressure of the surroundings dramatically increases. If the diver ascends back to the surface too rapidly, surrounding pressure decreases extremely rapidly, exerting stress on the equilibrium and causing it to shift towards the gaseous nitrogen, in turn creating bubbles in the diver’s bloodstream.
Fortunately, using the same principle that causes this problem can be reversed to solve this problem. To restore the equilibrium to its original state, the diver must be put back under pressure that simulates the conditions present underwater. Pressure can then be very slowly tapered down back to normal atmospheric pressure (typically at a slow rate of 1 atm per second). This effect causes the equilibrium to restore to its original state and converts the gaseous nitrogen in the diver’s blood to return to a dissolved, aqueous state.