Planets general properties

Beyond using no added solvent in a reaetion or proeess, water is probably the greenest alternative we have. In faet, before the industrial and ehemieal revolutions in the nineteenth and early twentieth eentury, water was probably the most widely used medium for a wide range of applieations. It is the most eommon moleeule on the planet and therefore the eheapest solvent we ean use, so it may seem somewhat surprising to non-ehemists that it is not more widely used. To understand when and why water is an ideal solvent for some proeesses and when it would be detrimental, we must first eonsider its general properties as a solvent. 

Equations (9.2.4), (9.2.5), (9.2.7), and (9.2.9) are sufficient for describing the motions of a planetary atmosphere. The vector notation used in these expressions is convenient for the study of their general properties, but for most applications it is necessary to write the equations in a specific coordinate system. Eor some calculations, a local rectangular system may suffice. More generally, spherical coordinates are employed with the origin at the center of the planet and the polar axis coincident with fi. hi this coordinate system, the equations take the form... 

A second unexpected property of water is that it expands when it freezes. Water has its maximal density, mass per unit volume, at 4°C. As it is cooled further, it begins to expand. Ice at 0°C occupies about 11% more volume than does liquid water at the same temperature. In this respect water is nearly unique. Almost all other liquids contract when they freeze, as we would expect since the solid phase is generally more compact and more ordered than the liquid phase and, hence, is denser. This behavior is not just a laboratory curiosity the fact is that our life on this planet is dependent on this remarkable property. This point has been elegantly stated by L. J. Henderson, a leading biochemist in the early twentieth century, in his thoughtful book The Fitness of the Environment which he wrote in 1913 Here are his words. 

The properties of supercritical fluids are generally different from those of regular fluids. For example, supercritical water is relatively nonpolar and acidic. Further, the properties of a supercritical fluid, such as its density and viscosity, change with changing pressure and temperature, dramatically as the critical point is approached. Thus, carbon dioxide is not listed in Table 6.1 because it has no liquid phase at terran atmospheric pressure. Carbon dioxide has a critical temperature of 304.2 K and pressure of 73.8 atm, however. It is therefore a supercritical fluid above that pressure, and may even exist as a potential biosolvent for rocky planets having the approximate mass of Earth (or Venus). 

Perhaps the most important connection between the two men was Halley s use of Newton s theory of gravitation to explain the motion of comets. Within a decade of the publication of the Principia, the scientific world had become convinced of the value of his theories in the explanation of the motion of the planets and of the Moon around the Earth. The same theories also explained a number of well-known physical phenomena that occur here on Earth. Scientists were not so certain, however, that Newton s theories had more general application, such as to the motions of stars, comets, meteors, and other astronomical objects. When Halley undertook to study the orbital properties of the comet of 1682, he was able to show that Newton s theories had much broader applications than had previously been appreciated. 

While there certainly must have been complications, such as radial mixing of material and non-equilibrium condensation and grain destruction, the equilibrium condensation sequence is generally consistent with the observed properties of the planets and meteorites. 

Neptunium was the first of these to be synthesised it was obtained in traces by bombardment of U(238) with neutrons (see Fig. 9(a), p. 318). Its chemical properties are not in general like those of rhenium or the other elements of Group vii. It yields no volatile oxide corresponding to RejO,. It functions with valencies 3, 4, 5 and 6 and in its higher stages of oxidation it tends to resemble uranium. Several isotopes are known including 237, 238 and 239. It was named after the planet Neptune discovered in 1846. 

Generally speaking, the term noise describes the random fluctuations of a property around a mean value. Noise can be of various kinds, from acoustic to meteorological, or even associated with the rotation speed of planets. 

It is so often stated that water is a ubiquitous liquid on earth and a general solvent for many kinds of solutes that such statements sound as clichds. Nevertheless, they are correct and merit discussion. Other common statements are that the properties of water are unique among liquids and are difficult to understand No one really understands water. It s embarrassing to admit it, but the stuff that covers two-thirds of our planet is still a mystery. Worse, the more we look, the more the problems accumulate new techniques probing deeper into the molecular architecture of liquid water are throwing up more puzzles. (Ball 2008). Unfortunately, to date this situation keeps being rather true and should be accorded a more comprehensive treatment. 

---