Henry's Law?

[eab]

I'm taking PADI's divemaster physics exam on Wednesday. Boyle, Charles and Dalton all seem to have a nice, straight forward formulas that I can memorize, but I just don't get what I'm supposed to know about Henry's Law. Am I just supposed to know about saturation and supersaturation?

Anyone out there taken this test and recall?

There are only three questions in the workbook. Is that really all there is for this?

Thanks tons!

 

[Drew Sailbum]

Henry's Law has everything to do with why we on-gas nitrogen during a dive and why we are able to off-gas during the surface interval.

Henry's Law: the amount of a gas that dissolves in a liquid is proportional to the partial pressure of the gas over the liquid, provided no chemical reaction takes place between the liquid and the gas. The Columbia Encyclopedia, Fifth Edition Copyright �1994, 1995 Columbia University Press.

As you descend, the ambient pressure rises and your lungs would collapse except that your regulator supplies air at the same pressure. Your lungs are now inflated, but the absolute pressure of air has increased. And as the absolute pressure of air increases, the partial pressure of the nitrogen and oxygen has also increased.

Your body is primarily liquid, and Henry's Law describes what happens next. The increased partial pressure of nitrogen in your lungs results in more nitrogen disolving into your tissues.

If you could stay down long enough, this would presumably reach saturation at the point where the ratio of the amount of nitrogen dissolved in your tissues (call it N2body) to the partial pressure of nitrogen in your lungs (call it N2lungs) would be the same as it would be on the surface pre-dive.

If I were to boil this down to an equation, it would be that:
dissolved N2(1) : ppN2(1) = dissolved N2(2) : ppN2(2)
where the dissolved N2 is a measure of the amount of nitrogen dissolved in saturated tissue

 

[eab]

I'm still new at this scubaboard stuff, so I can't do the quote with the larger text you have in the formula. BUT, and that's a big but, I understand what you said. That's way more important.

Thanks. My brain just works so much better with formulas. Oddly, I could remember Avogadro's number from my high school physic's class and that was too many years ago!