Ch 12 How much heat does your body lose when 2.2 g of sweat evaporates from your

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

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