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These are extremely simple questions — basic biology — but I would like to make sure that the way I have answered is at the very least correct.

  1. Hydrogen bonds are very weak, so how is it possible that they are so important in the properties of water? Hydrogen bonds in water provide many characteristic benefits to water: cohesion (holding water molecules together), high specific heat (absorbing heat when breaking, releasing heat when forming; minimizing temperature change), high heat of vaporization (several hydrogen bonds must be broken in order to evaporate water), lower density of ice (molecules in ice are spaced farther apart), and solubility (polar molecules are attracted to ions and polar compounds, making them soluble in water).
  2. Why do we feel cooler immediately after we go swimming than we do after we have fully dried off? We feel cooler immediately after we go swimming than we do after we have dried off because it takes a lot of heat to evaporate water; however, once we dry off we remove much of the water from our skin, and the water is evaporated much more quickly.
  3. If water were non-polar, would our temperature heat up less quickly or more quickly if we went outside on a hot day? Why? More quickly. Because hydrogen bonds within water slow down the movement of molecules and allow for water to have a very high specific heat.
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  • $\begingroup$ General chemistry questions are off-topic on Biology.SE, but instead should be asked at Chemistry. $\endgroup$ – MattDMo Sep 1 '14 at 2:43
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  1. You are saying what hydrogen bonds are doing, not why are they able of such achievements, despite being so weak. Their strength is in numbers. At room temperature, fully one fifth of the water molecules are engaged in four bonds with other water molecules, while the remainder forms two such bonds. (More detail at http://www1.lsbu.ac.uk/water/hbond.html ). In contrast, hydrogen sulfide forms essentially no hydrogen bonds with other hydrogen sulfide molecules, despite significant similarity between oxygen and sulfide. The difference in size between oxygen and sulfur makes the former much more electronegative. I could go on with other hydrogen compounds, but the fact that answers your first question is: each water molecule is involved in a series of bonds with other water molecules, on an unequaled scale.

Also, hydrogen bonds are stronger, pickier about distance and angle than the alternatives available to other molecules (dipole-dipole, van der Waals etc.) So even if they seem feeble, and even if the alternatives were as plentiful as hydrogen bonds, the latter would still be more capable of tying up molecules.

  1. The effect of water drying (which comes after swimming, but also after sweating, bathing, or cleaning oneself with a hot oshibori) is caused by water evaporation. Each state transition, including that from liquid water to air-borne vapors, is a heat-consuming phenomenon. When skin dries, the heat to turn water into vapors has to come from somewhere. In perspiration's case, it is one's body.

Note that cooling down while water evaporates is not only something we feel, but a physical reality, occurring even in innate systems. For example, Amazon forests and Sahara are similarly close to the Equator, but the former is cooler than the latter, in part because heat it receives is in part used up to evaporate water.

Your answer was good.

  1. Again, you are right. Were water non-polar, it would have lower latent heat, or, in lay terms, it would evaporate without much heat consumption. Were sweat made of a non-polar liquid, it will fail to consume heat when evaporating, leaving one to warm up sooner / faster.
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