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# What is the relative humidity in the lungs? Express as a percentage with no units.?

Suppose that air in the human lungs has a temperature of 37 degrees C and the partial pressure of water vapor has a value of 5.5 x 10^3 Pa.

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- nealjkingLv 61 decade agoFavorite Answer
The relative humidity is calculated by dividing the partial pressure (5.5e3 Pa) by the saturated partial pressure of water at the same temperature.

The reference below gives a table of the saturated vapor pressure and also a formula:

Saturated VP = [e^(77.3450 + (0.0057)T - (7,235)/T]/T^(8.2)

The formula gives a value of 6258 Pa at T-c = 37 (implies the absolute temperature = 310.15).

So the relative humidity would be = 5500/6258 = 87.9%.

Hmmph, I would have guessed that the answer should be 100%: after all, the air in your lungs is in intimate contact with the blood.

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