The Royal Society of Chemistry is offering £1000 (~ $1550 US) to anybody who comes up with the best explanation for why hot water freezes faster than cold water, a conundrum that has baffled scientists for centuries.
The reward will go “… to the person or team producing the best and most creative explanation of the phenomenon, known today as The Mpemba Effect.” The deadline for submissions is July 30, 2012, and submissions must be made here.
For this contest, it seems to me that a non-scientist may stand a good chance of winning the prize (after all, scientists have been unsuccessful for over two-thousand years!), so I thought I’d throw a few factoids about water into the Webosphere as basic background for any creative geniuses that might like to try their hand at submitting, but would like somewhere to begin their far-flung theories (which, the website notes, must be “…scientifically sound and arresting in presentation and delivery”).
The following factoids are all interconnected characteristics of the substance that is the basis for most life on our planet. If the characteristics of water were different, none of us would be here; or, at the very least, we would be far different beings*…
[image found at sguforums.com]
Oxygen is more electronegative than hydrogen and the molecule forms an ‘electrical dipole’, with the oxygen end more negative, and the hydrogen end more positive; therefore, water molecules are attracted to one another and readily form connective bonds, which gives water some of its interesting characteristics, such as its ability as a ‘universal’ solvent, and its high surface tension (this is why there is a meniscus at the surface, and why insects can walk on water). To be more specific, water molecules form a ‘V’ shape (some people call it a ‘U’ shape), with the hydrogen atoms at the two top tips of the ‘V’ pointing away from the oxygen (oxygen has extra valence electrons which ‘push’ the electropositive hydrogen atoms away, and the hydrogen atoms repel each other — they are both electropositive — thereby forming the ‘V’ shape).
The melting point of water decreases as a function of pressure. The triple point is a certain temperature and pressure at which all three phases of a substance — solid, liquid and gas — occur in a stable equilibrium (for water, the triple point is 0.01 °C and 611.73 pascals). For most substances, the triple point is the minimum temperature at which the liquid phase can occur; however, for water, the melting point decreases as a function of pressure.
[image found at SWE.org]
The volume of water increases from liquid to gas and from liquid to solid. Conventionally, molecules disperse into gaseous form when heated, condense into a liquid phase when cooled, and condense to a greater density when cooled further. These phase changes, or changes in state, correspond to energy changes; from high energy (gas) to medium energy (liquid) to low energy (solid). Water, however, is a bit of an individualist. When water vapor is cooled, it condenses into a liquid, but when water is cooled to 4°C (39 °F), its volume begins to increase slightly; further, when it reaches 0°C (32 °F), it begins to expand radically, becoming less dense (this is why ice cubes float in a glass of water). This odd characteristic of water is related to its shape and how molecules bond together (see above: Water is a polar molecule). As a liquid, water molecules move about quite readily; the individual molecules form bonds, bonds are broken, and bonds are re-formed, thereby giving water its fluidic properties. When water is cooled to 4°C, the energy of the molecules decreases until they become very closely packed, but at 0°C, the molecules begin to align in a hexagonal, crystal lattice that increases the volume of a given sample of water (e.g.: water in an ice-cube tray) because individual molecules are held farther apart, with more empty space between them.
For your submission, you may want to thow in some psycho-babble regarding quantum states (in particular, Heisenberg’s Uncertainty Principle), Schrödinger’s cat though-experiment (the observer is part of the experimental system: you don’t know the water is frozen until you actually observe it), chemical kinetics (e.g.: does the higher temperature of water act as a catalyst, creating more collisions or larger spaces between molecules, thereby yielding more bonding potential for ice’s hexagonal, crystal lattice structure?), and maybe even some hand-waving about sublimation (transformation directly from gaseous to solid form).
Best of luck with your submission!!!
*I found this cartoon in an old textbook; Biology, IV Ed., by Helena Curtis