My question I have to answer is: A runner picks up pace on a warm day and starts sweating profusely. What property of water explains how sweating helps the runner continue running?

The following are four options I have to choose from to answer this question, and below that is the uncertain answer I chose.

A. Since water molecules are polar, they adhere to the surface of the skin, which allows cooling. The skin’s outer layer of dead cells enables the adhesion.

B. At elevated body temperature, the hydrogen bonds in water break, which allows water to escape as vapor. This causes heat loss in the body, which lowers body temperature.

C. Hydrogen bonds rearrange at higher temperatures and form a lattice structure that requires energy. This energy use lowers the heat in the body.

D. Sweating is due to the high heat capacity of water. When sweating increases, heat is released and the body temperature is lowered.

I chose (B), as (A) and (C) do not make sense and that (D) I think requires too much amount of time since water has a high heat capacity. Sweating, especially during running, is more immediate than (D). Would (B) be the correct answer?

  • $\begingroup$ I think the answer will be B and D. B explains the process of evaporation and D explains why water is a good choice of a liquid to evaporate. $\endgroup$ – Roni Saiba Oct 28 '20 at 12:19
  • $\begingroup$ @Oosaka No, I understand the detailed explanation of how water evaporating leads to cooling. I didn't want a simple answer with no explanation, no. I suppose I was trying to ask why an answer such as A or D wouldn't work, because I feel these answers could have some merit unless I'm wrong. Finding only one correct answer choice was unclear. Do you think they have some merit, or is it definitely clear that B is correct? $\endgroup$ – Renée Oct 28 '20 at 15:33
  • $\begingroup$ @Roni Saiba: No, water is the only choice for a liquid to evaporate because there's a lot of it in humans (and other animals). Other liquids, for instance alcohol, would actually provide better cooling since they evaporate at lower temperatures, but they don't exist in the body in significant quantities. $\endgroup$ – jamesqf Oct 28 '20 at 16:53
  • $\begingroup$ @jamesqf But wont same volume of water carry more heat after evaporation than alcohol because of higher heat capacity? I apologize for my shortcomings in understanding physics. $\endgroup$ – Roni Saiba Oct 28 '20 at 18:22
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    $\begingroup$ @Renée Thank you for clarifying. I agree with you that D sounds technically correct (as I said), and assuming the teacher sees it as incorrect for some reason, I am curious as to what that reason is. A strikes me as incorrect because the water adhering to the skin isn't useful, it is in fact its evaporation is what helps, and I don't know of dead cells helping with evaporative cooling at all. Maybe the idea is that water needs to be in contact with the skin to draw heat from the body as it evaporates, but how much does that play? IIRC skin is hydrophobic to begin with. So, seems clearly wrong. $\endgroup$ – Oosaka Oct 29 '20 at 11:34

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