Ch 12 How much heat does your body lose when 2.2 g of sweat evaporates from your
ID: 975320 • Letter: C
Question
Ch 12 How much heat does your body lose when 2.2 g of sweat evaporates from your skin at 25 C? (Assume that the sweat is only water.) The heat of vaporization of water at 25 C is 44.0 kJ/mole. Express your answer using two significant figures.
B The human body obtains 810 kJ of energy from a chocolate chip cookie.If this energy were used to vaporize water at 100 C, how many grams of water could be vaporized? The heat of vaporization of water at 100 C is 40.7 kJ/mole. (Assume that the density of water is 1.0 g/mL.)
Explanation / Answer
Assuming sweat is a water only,
The Number of moles of water = Weight / mol wt
= 2.2 / 18 = 0.1222 moles of water.
Heat lost = No. of moles Of water x Heat of vapourisation
= 0.122 x 44.0
= 5.368 KJof heat is lost from body.
B) Heat obtained = 810KJ
The number of moles of water = Energy obtained / Heat of vapourisation
= 810 / 40.7
= 20.04 moles of water
Now we can convert this no. of moles to gram by relation,
Moles = Gram / mol. wt. therefore
Gram = Moles x mol. wt of water
= 20.04 x 18
= 360.89 g of water
= 360.89 x 1 ( density ) = 360.89 mL of water is vopourised