Question

Evaporating sweat cools the body because evaporation is endothermic and absorbs 2.44 kJ per gram of water evaporated. Estimate the mass of water that must evaporate from the skin to cool a body by 0.40 ∘C, if the mass of the body is 99 kg and its heat capacity is 4.0 J/g∘C. (Assume that the heat transfer is 100 % efficient.)

Answer 1

Mass of the body = 99 kg = 99000g

Heat capacity = 4.0 J/g°C

∆T = 0.40°C

So, energy released

= mass x heat capacity x ∆T

= 99000 x 4.0 x 0.40

= 158400 J

= 158.4 kJ

Heat required for evaporation = 2.44 kJ/g

So, the mass of sweat evaporated

= 158.4/2.44

= 63.7 g

Or 64 g

Comment if any problem