Dihydrogen Monoxide: A Strange Substance

Dihydrogen momoxide (aka Water) is an extremely common substance we all know about – or do we? Some odd properties of water:

  • It has a much higher heat capacity than most substances. Heat capacity is the quantity of heat which must be applied to raise the temperature of a given amount of substance by, say, one degree Celsius (or Fahrenheit). For example, it takes about one calorie of heat to raise the temperature of one gram of water from 25 degrees Celsius to 26 degrees, By contrast, only about 0.2 calorie would be needed to raise a gram of aluminum by 1 degree C, and even less to do the same thing to a gram of iron. The heat capacity of air is, also, much lower than water. This is why we see highway signs telling us water on bridge surfaces freezes well before it does on road surfaces having soil under them (heat capacity of soil is greater than air). This property of water also explains why, after sundown, air temperature drops much lower in dry air, than in humid air. Obviously, this has a profound effect on climate. Think of heat capacity as the ability to retain heat. The higher moisture (water) content of humid air “holds” the heater better than dryer air.
  • Water is the only common substance whose liquid state is more dense than its solid state (ice). Ever wondered why ice floats? Density is a comparison of how much a substance weighs to the amount of room it occupies. Mathematically (don’t be alarmed, it’s simple) it’s defined as the ratio of mass to volume. One gram of liquid water occupies one milliliter (or cubic centimeter) of space. It’s density, therefore, is 1.0 gram per milliter. By contrast, a gram of ice takes up about 1.1 milliliter. Density of ice is 1.0 gram divided by 1.1 milliliter, or about 0.9 gram per milliliter. Densities less than 1.0 gram per milliliter float; densities greater than 1.0 gram per milliter sink. Because of this counterintuitive property of water, ice in lakes, ponds, or for that matter, oceans, will freeze, leaving a lower level of water beneath, whose temperature will not go below freezing, enabling marine life to survive winter.
  • Ever wonder why a steam burn is more painful than one from hot water? We probably learned the “formula” for water in grade school. H2O, right? Well, that’s something of an oversimplification. If water is simply two atoms of hydrogen bonded to an oxygen atom, the substance would be a gas at room temperature. Water is actually a loosely bonded bunch of individual H2O’s; the attractive forces holding the bunch together are called hydrogen bonds. The strength of a H-bond is only a fraction of the strength of the bonds within the molecule. When liquid water is heated to its boiling point (100 C;212 F). additional energy is needed to break the hydrogen bonds. This energy does not even register on a thermometer, but it’s there, all right. The steam has more energy to burn you as a result.
  • Once water is boiling, you can’t raise its temperature above the boiling point, no matter how much heat you (or the stove) applies. Boiling points can only be raised by increasing barometric pressure. If one constructs a pot with a tight lid, the steam has no place to go, the pressure in the pot goes up and the boiling point will increase. In a kitchen, this pot is a pressure cooker. The hotter boiling water cooks stuff much faster as a result.

Hope this makes some sense. Ain’t science wonderful!

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