November 18, 2013

On the Nature of Water - v) Phase Change

   We briefly mentioned the Water Cycle in the previous essay. At the Gaia scale, earth is a water planet. We know water in each of its single phases – solid, liquid and gas in a way beyond the common substance. We know also that there are some interesting thermodynamic properties of water that change as a function of temperature and pressure, and to a very limited extent, volume. The volume of water makes a highly interesting case study – as the volume near the freezing point is not the linear response that we might expect.

    Let us arbitrarily walk the water phase diagram from the cold side to the hot. We will start at -10oC for a start – the C refers to degrees on the Celcius scale, measured in centigrade units. This scale is different from the Fahrenheit scale that we use in the United States and the absolute temperature scale measured in Kelvin units. The three scales measure the exact same phenomenon, but have different range and utility. Centigrade is a base ten metric scale that has set points at 0oC for the freezing point of water and 100oC for the boiling point. This corresponds to 32oF and 212oF on the Fahrenheit scale – with an algebraic formula of F = 9/5C + 32 for the conversion. This places arbitrary measurement systems in conflict – a rite of passage in science. 
    The Kelvin scale is an offset of the Celsius scale to set the absolute zero at -273oC, such that the temperature measurement fit the same thermodynamic parameters as used in the calculations of entropy and enthalpy – giving absolute temperature rather than being relative to our earthly temperature frame. Absolute temperature 0 K is where all molecular motion theoretically stops.

    At absolute zero – the mass is extrapolated to a zero point and all packing is tight, close and regular. There is no vibration, no movement relative to other molecules – the lattice is continuous forever. As we climb by adding heat, we see the atoms wiggle, but there is not enough force to move them – the hydrogen atoms each bridging two oxygen atoms, the tetrahedral oxygen surrounded by four hydrogen atoms. One pyramid up, another down, about a central plane. The location of the molecule in space is fixed by the arrangement of each molecule to other molecules also held fixed – the bonding is extremely regular.

    Back to water, now as a molecular solid at minus ten degrees C. The bonding here is still very regular and tightly packed. If the water droplets have a confirmed border, the alignment can be seen as a stacking process from the interior, moving out from being fixed at a point of nucleation, a physical center. The first water molecule holds rigid as the molecular motion is constrained, and the molecules closer to this center are held tight – the ones further off are led less tight. The molecules are attracted to each other by polar forces between the negative oxygen end of one water to the positive hydrogen end of the next water – as the temperature has climbed – the molecules begin to vibrate. They cannot move out of the lattice – no translations or rotations are allowed.

    The vibration does not have enough energy contained at this point to break any of the hydrogen bonds. The actual chemical bonds of water do not break until we use enough energy to get hydrolysis of the water – the chemical breaking down of water to the component gases hydrogen and oxygen. This happens at an electrode in a contained system – when in nature it can take the form of creating ozone via lightning bolt. Hydrogen bonds hold water molecules together and are not like atomic bonds between elements.

    Things that are dissolved in water disrupt the lattice of molecules and cause freezing point depression and boiling point elevation. The pressure is also a factor – but for solids and liquids, the volume is consistent and pressure is not a factor. There are several different ice phases that have different unit cell packing, but the ice we know in the form of cubes has a regular structure similar to our current description. The surface starts to melt as we approach zero degrees C (32 degrees F), due to the bending and stretching of the individual water atoms. These modes can be controlled by frequency to vibrate in tandem and these characteristic frequencies tend to be harmonics of the bond lengths and angles.

    Liquid water forms as the ice melts. The temperature remains at zero C until all of the ice has melted to water. The ice is less dense than the water at zero C and floats on the top of the liquid water surface. This is odd for a liquid, but make the fish very happy, as they can reside under the ice in a lake or pond and live perfectly well. If ice froze in a solid mass from bottom to top, then we would have frozen fish in history and empty oceans today. Water has a minimum volume at 4oC, as the molecules slowly rotate their conformation when not fixed directly to the next water's atoms. 
    In the rising temperature liquid, the water molecules can traverse past each other using rotational and translational energy provided by the energy as measured at higher temperature. The water on the top surface exchanges molecules with the air – each temperature has a dynamic equilibrium value where the evaporation off the surface is equal to the landing rate on the surface – when there is more energy present, the temperature goes up and there is always excitement of chaos caused by increased molecular motion.

    Water has three individual modes of vibration – the bond angle bending, the symmetrical stretch of the two O-H bonds and the asymmetric stretch of the same bonds. These modes have an infrared frequency vibration that is shifted when water is bound to a metal atom or an organic molecule that is not water. This phenomena is concentration dependent and can be washed out in dilute solution. As concentration increases, the direction of water is mitigated by what the water contains and the vibrations begin to take on characteristic frequencies of the substances dissolved in the water, rather than the spectrum of the water itself.

    In liquid water, we tend to get translational and rotational phenomena along with or vibrational energy. Hot water spins the atoms around relative to each other and passing molecules cause friction, which generates more heat as heat is added. The temperature rise is consistent with energy input – one gram of liquid water increases one degree Celcius of temperature in the heat measurement called a calorie. This is one thousandth of a Calorie – the unit that we measure food energy content as a function of weight. People spend too much time watching their caloric intake rather than exercising and using the energy of their food content. Drinking water is a way of keeping hydrated and allowing your internal systems to balance themselves.

    Evaporation occurs at the air-water interface on any surface. This is counterbalanced by condensation – where the air is saturated with water to the point where the gas condenses and rain falls, as a function of temperature. When the air contains moisture and the light hits it from behind, a prism of color is generated – creating the rainbows that thrill us with their appearance. This is a diffraction of white light into components in the visible region of the spectrum – the narrow band that contains the drummer whose beat we march to on the current scale. The rainbow is a non-discriminatory form of sorting and separating – it holds no value judgment except for that occasional pot of gold at the end.

    When water reaches the boiling point, the molecules on the surface leave at a rate where they are not replaced in an equilibrium exchange. Evaporation occurs at a rate proportional to the added heat and the temperature remains at 100oC (212oF) until all of the water is turned to steam. The contained steam then rises in temperature and the hot gaseous water holds enough energy to do significant work. The steam engine was a crucial invention in modern progress – as we transverse the reversal of the fossil fuel energy bonus, we will likely once again make use of all our water – not as a trash and sewage receptacle, but rather as an integral resource in the operating system of climate regulation for the populations of Gaia.

    The water of earth is the blood fluid of a larger conscious creature that operates on a different scale than we currently imagine. If the entire scale of everything is mapped to a concrete form – the very largest things and the infinitely smallest things are all the same things – as above, so below. Imagine a giant mobius strip that runs in a cyclic loop, embedded within another mobius strip with a larger loop, etc. – radiating in waves from a central infinity – a small crossing on a scale of one alongside a massive crossing on a scale of all, as one.

Namaste' ...  doc 04/16/13

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