A hiker caught in a rainstorm might absorb 1 liter of water in his clothing. If

Question

A hiker caught in a rainstorm might absorb 1 liter of water in his clothing. If it is windy so that this amount of water is evaporated quickly at 20 degree C, how much heat would be required for this process? Delta H_vap(H_2O) = 44.106 kJ/mol If all this heat were removed from the hiker (no significant heat was generated by metabolism in this time), what drop in body temperature would the hiker experience? The clothed hiker weighs 60 kg and you can approximate the heat capacity of hiker and clothes as equal to that of water. C(H_2O) = 4.184 J /C g (The conclusion from this calculation is to stay out of the wind if you get your clothes wet.) How many grams of sucrose would the hiker have to metabolize (quickly) to replace the heat of evaporating 1 liter of water, so that his temperature did not change? You can use the heats of reaction at 25 degree C; the reaction is: sucrose(s) + oxygen(g) rightarrow carbon dioxide(g) + water (1) If you set out to explore the surface of the moon, you would want to wear a space suit with thermal insulation. In such activity you might expect to generate roughly 4 kj of heat per kilogram of mass per hour. If all this heat is retained by your body, by how much would your body temperature increase per hour owing to this rate of heat production? (Assume that your heat capacity is roughly that of water.) C(H_2O) = 4.184 J/C.g What time limit would you recommend for a moon walk under these conditions? Explain

Explanation / Answer

1)

mass of water = 1000 g

moles of water = 1000 / 18 = 55.55

delta H vap = 44.106 kJ/mol

Q = n x delta Hvap

    = 55.55 x 44.106

    = 2450 kJ

Q = 2450 kJ

b)

Q = m Cp dT

2450 x 10^3 = 60000 x 4.184 x dT

dT = 9.76 oC

c)

1 mol sucrose releases ------------ 5644 kJ heat

?? mol of sucrose         --------------> 2450 kJ

moles of sucrose = 2450 / 5644

                              = 0.434

mass of sucrose = 0.434 x 342

                              = 148.4 g

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