A resting adult of average size converts chemical energy infood into internal energy at the rate of 120 W, called herbasal metabolic rate. To stay at a constant temperature,energy must be transferred out of the body at the same rate.Several processes exhaust energy from your body. Usually the mostimportant is thermal conduction into the air in contact with yourexposed skin. If you are not wearing a hat, a convection current ofwarm air rises vertically from your head like a plume from asmokestack. Your body also loses energy by electromagneticradiation, by your exhaling warm air, and by the evaporation ofperspiration. Now consider still another pathway for energy loss:moisture in exhaled breath. Suppose you breathe out 25.0 breaths per minute, each with a volume of0.600 L. Suppose also that you inhale dry air and exhale air at37°C containing water vapor with a vapor pressure of3.40 kPa. The vapor comes from theevaporation of liquid water in your body. Model the water vapor asan ideal gas. Assume its latent heat of evaporation at 37°C isthe same as its heat of vaporization at 100°C. Calculate the rate at which you lose energy by exhaling humid air.

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