During exercise, a person may give off 184 kcal of heat in 33 min by evaporation of water from the skin. How much water has been lost? (Assume a temperature of 20°C.)
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During Exercise a person may give off 184 kcal of heat in 33 min….?
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Tags: Exercise
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1 gintable //
(Assume a temperature of 20°C.) YEAH RIGHT (sarcasm)! The human body is at 37 Celsius.
The heat is involved is used evaporating the water at a constant temperature of 37 Celsius.
How is this possible when water boils at 100 C? Well, it evaporates at off the skin to become water vapor at a partial pressure within the atmosphere.
If the human body needed to raise its sweat to 100 C before boiling it off, we’d be dead after any workout not in cold weather.
Q = m*h_vap(T)
h_vap is a function of the temperature. Looking it up in steam tables (assuming the salt content doesn’t change it)
h_vap = 2.413*10^6 J/kg
Solve for m:
m = Q/h_vap
Converting Q from kcal to Joules:
Q=770371 J
Result:
m=0.3193 kilograms
of water loss as sweat