Expired air is saturated with water vapor and generally contains more of it than does inspired air. There is usually a net loss of water from the body due to breathing. Water vapor pressure in the at saturation in the lungs (at 37°C) is 47 mmHg, while in expired air at 33°C it is 37.7 mmHg. Consider the case of someone who is breathing dry air in and moist air out at a rate of 15,000 L/day. This corresponds to a mean respiratory minute volume of 10.4 L/min, and to a fairly typical daily metabolic rate. The atmospheric pressure is 760 mmHg (i.e., standard pressure). Since 1 mol (18 g) of water vapor occupies 22.4 L at standard temperature and pressure, 1 L has a mass of 18/22.4 = 0.80 g. Ignoring air volume corrections, what is the daily rate of water loss (in g) if the air is inspired completely dry and expired saturated with water vapor at (a) 37°C and (b) 33°C? Note that solving this problem involves several steps. The professor and TA will help with this if you have difficulty with it. Recall from chapter 21 that you can determine the fractional concentration of a gas if you know its partial pressure and the total pressure (Px = Fx × Ptotal). So you can determine the fractional concentration of water vapor in exhaled air at each temperature. Next, because you now the total volume of air exhaled in a day, you can determine the amount of water vapor exhaled per day. Finally, because you know the mass of water vapor per liter, you can determine the mass of exhaled water vapor. As always, be careful that the units work out properly.
Ideal and Real Gases
Ideal gases obey conditions of the general gas laws under all states of pressure and temperature. Ideal gases are also named perfect gases. The attributes of ideal gases are as follows,
Gas Laws
Gas laws describe the ways in which volume, temperature, pressure, and other conditions correlate when matter is in a gaseous state. The very first observations about the physical properties of gases was made by Robert Boyle in 1662. Later discoveries were made by Charles, Gay-Lussac, Avogadro, and others. Eventually, these observations were combined to produce the ideal gas law.
Gaseous State
It is well known that matter exists in different forms in our surroundings. There are five known states of matter, such as solids, gases, liquids, plasma and Bose-Einstein condensate. The last two are known newly in the recent days. Thus, the detailed forms of matter studied are solids, gases and liquids. The best example of a substance that is present in different states is water. It is solid ice, gaseous vapor or steam and liquid water depending on the temperature and pressure conditions. This is due to the difference in the intermolecular forces and distances. The occurrence of three different phases is due to the difference in the two major forces, the force which tends to tightly hold molecules i.e., forces of attraction and the disruptive forces obtained from the thermal energy of molecules.
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