Friday, February 24, 2012

Water's Anomalies

One of my temptations as a science classroom teacher was to devote unequal time to curricular topics for which I had a special fondness. The district curriculum, of course, outlined the topics to be covered. Time requirements for sub-topics were not rigorously spelled out. Sometimes I found myself covering certain topics in astronomy and meteorology more extensively, because those topics were especially fascinating for me.

Within the weather unit, water was an ever-present topic of relevance. Using just one example, water has unique properties with respect to its ability to hold and distribute heat energy. A catalog of water’s behavior when heat flows in or out, resulting in temperature change, state change, or changes in a large variety of other properties, would fill volumes. With varying degrees of success I resisted the temptation to make the study of water a full-fledged, self contained mini-unit. Notwithstanding, several topics relating to the multiple, unexpected anomalies of water assumed front and center standing in my classroom for a few days each year.

For instance, it is well known that matter expands when heated and contracts when cooled. Welcome to an anomaly provided by water. (An anomaly is defined as an unexpected outcome, deviating from what is standard, normal, or expected.) At a narrow, commonly experienced temperature range in earth’s temperate zones where a vast majority of earth’s population resides, the expected behavior of water is sometimes turned on its head. Water contracts as it is cooled toward 39˚F. But when water is gradually cooled below 39˚F it begins to expand, and finally expands dramatically when it freezes solid upon reaching 32˚F.

The grief of burst winter water pipes aside, this behavior has many beneficial effects. Because of the polarity of water molecules (explained in our last post), water molecules slowly begin to assume a hexagonal, crystalline structure below 39˚ F. Then they suddenly lock into the complete, rigid crystalline structure when the 32˚ freezing temperature is reached. The ice expands greatly, becoming only 91% as dense, because a little extra space is formed within the hexagonal crystalline structure. Ice forms, therefore, at the top of a water body and our ice cubes float atop our beverages.

There is much more to know. Come spring, the geometric structure breaks down almost completely when the ice melts. The water is now denser and begins to sink toward the lake bottom. When water warms to 39˚F it is densest because the crystalline structure has broken down completely. Heated above 39˚F other factors take over and the water begins to expand, becoming less dense, and remaining at the top of the water. What is the upshot of water being least dense at 32˚F? In winter we skate on ice at the top of the lake. The ice also acts as an insulating layer for the water beneath. The bottom of the lake remains at 39˚F all year long, providing a constant environment for fish which require such conditions. The warmest water is at the bottom of the lake in winter but at the top of the lake in summer. Swimming is more enjoyable.

This post is not meant to create technical expertise among my readers. Its purpose is, however, to inspire wonder and curiosity. We wonder, “Why does such a plentiful, common, even 'plain' substance such as water possess such a wealth of unusual and unexpected properties?” The answer lies in understanding that water must have its set of unique properties in order to sustain the life of earth’s many creatures, great and small, including man.

We might ask why the 105˚ angle of the two hydrogen atoms with the single oxygen atom in the water molecule results in a certain set of properties for water. In most questions of this sort, we could respond that Condition A is followed by Result B. We could also respond that changing Condition A would change Result B in some respect and perhaps offer some explanation. But why did Condition A result in a particular Result B in the first place? There is no real reason except to say that physical constants and the laws of nature dependent on them are out of man’s control. They are under divine control. Man is primarily an observer and ultimately, a consumer. Man’s activities depend on the Designer who lovingly provides us opportunities for utilizing His designs.