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From Wikipedia

Superheated water

Superheated water is liquid water under pressure at temperatures between the usual boiling point (100°C) and the critical temperature (374°C). It is also known as subcritical water and pressurized hot water. Superheated water referred to in this article is stable because of an applied over pressure which raised the boiling point, or by heating in a sealed vessel with a headspace, where the liquid water is in equilibrium with vapour at the saturated vapor pressure. This is distinct from the use of the term superheating to refer to water at atmospheric pressure above its normal boiling point, which has not boiled due to a lack of nucleation sites (sometimes experienced by heating liquids in a microwave).

Many of the anomalous properties of water are due to very strong hydrogen bonding. Over the superheated temperature range the extensive hydrogen bonds break down, changing the properties more than usually expected by increasing temperature alone. Water effectively becomes less polar and behaves more like an organic solvent such as methanol or ethanol. Solubility of organic materials and gases increases by several orders of magnitude and the water itself can act as a solvent, reagent and catalyst in industrial and analytical applications, including extraction, chemical reactions and cleaning.

Change of properties with temperature

All materials change with temperature, but water shows changes which are much greater than would be expected from temperature considerations alone. Viscosity and surface tension of water drop and diffusivity increases with increasing temperature.

Self-ionization of water increases with temperature, and the pKw of water at 250°C is closer to 11 than the more familiar 14 at 25°C. This means that the concentration of hydronium ion (H3O+) is higher, and hence the pH is lower (although the level of hydroxide (OH-) is increased by the same amount so the water is still neutral). Specific heat capacity at constant pressure also increases with temperature, from 4.187 kJ/kg at 25°C to 8.138 kJ/kg at 350°C. The dielectric constant (relative permittivity) decreases significantly as the temperature rises, which has a significant effect on the behaviour of water at high temperatures.

Explanation of anomalous behaviour

Water is a polar molecule, where the centers of positive and negative charge are separated. In an applied electric field, the molecules align with the field. In water, the extensive hydrogen bonded network tends to oppose this alignment, and the degree to which this occurs is measured by the relative permittivity. In water, polarity shifts are rapidly transmitted through shifts in orientation of the linked hydrogen bonds, and therefore water has a high relative permittivity, about 80 at room temperature. This allows water to dissolve salts, as the attractive electric field between ions is reduced by about 80 fold. As the temperature increases, the thermal motion of the molecules disrupts the hydrogen bonding network, and therefore the relative permittivity decreases with temperature, to about 7 at the critical temperature. At 205°C the relative permittivity has fallen to 33, the same as methanol at room temperature. Thus from 100°C to 200°C water behaves like a water / methanol mixture. The disruption of the extended hydrogen bonding is also responsible for much of the anomalous behaviour of superheated water, as extra energy needs to be supplied to break the bonds (increased heat capacity), and the molecules move more freely (viscosity, diffusion and surface tension effects).

Solubility in superheated water

Organic compounds

Organic molecules often show a dramatic increase in solubility in water as the temperature rises, partly because of the polarity changes described above, and also because the solubility of sparingly soluble materials tends to increase with temperature as they have a high enthalpy of solution. Thus materials generally considered “insoluble� can be very soluble in superheated water. The solubility of PAHs is increased by 5 orders of magnitude from 25°C to 225°C and naphthalene, for example, forms a 10% wt solution in water at 270°C, and the solubility of the pesticide chloranthonil with temperature is shown in the table below.

Thus superheated water can be used to process many organic compounds with significant environmental benefits compared to the use of conventional organic solvents.

Salts

Despite the reduction in relative permittivity, many salts remain very soluble in superheated water until the critical point is approached. Sodium chloride, for example, dissolves at 37 wt% at 300°C As the critical point is approached, the solubility drops markedly to a few ppm, and salts are hardly soluble in supercritical water. Some salts do show a reduction in solubility with temperature, but this behaviour is less common.

Gases

The solubility of gases in water is usually thought to decrease with temperature, but this only occurs to a certain temperature, then solubility increases again. For nitrogen, this minimum is 74°C and for oxygen it is 94°C Therefore gases are quite soluble in superheated water at elevated pressures. Above the critical temperature, water is completely miscible with all gasses. The increasing solubility of oxygen in particular allows superheated water to be used for the wet oxidation processes

Corrosion

Superheated water can be more corrosive than water at ordinary temperatures, and at temperatures above 300°C special corrosion resistant alloys may be required, depending on the other components dissolved in the water. However, continuous use of carbon steel pipes for 20 years at 282°C has been reported without significant corrosion, and stainless steel cells showed only slight deterioration after 40-50 uses at temperatures up to 350°C.

Density of air - Wikipedia, the free encyclopedia

At 20 C and 101.325 kPa, dry air has a density of 1.2041 kg/m3. ... The following table illustrates the air density - temperature relationship at 1 atm ... So when water molecules (vapor) are added to a given volume of air, the dry air ...


From Encyclopedia

Periodic Table of Elements PERIODIC TABLE OF ELEMENTS

In virtually every chemistry classroom on the planet, there is a chart known as the periodic table of elements. At first glance, it looks like a mere series of boxes, with letters and numbers in them, arranged according to some kind of code not immediately clear to the observer. The boxes would form a rectangle, 18 across and 7 deep, but there are gaps in the rectangle, particularly along the top. To further complicate matters, two rows of boxes are shown along the bottom, separated from one another and from the rest of the table. Even when one begins to appreciate all the information contained in these boxes, the periodic table might appear to be a mere chart, rather than what it really is: one of the most sophisticated and usable means ever designed for representing complex interactions between the building blocks of matter. As a testament to its durability, the periodic table—created in 1869—is still in use today. Along the way, it has incorporated modifications involving subatomic properties unknown to the man who designed it, Russian chemist Dmitri Ivanovitch Mendeleev (1834-1907). Yet Mendeleev's original model, which we will discuss shortly, was essentially sound, inasmuch as it was based on the knowledge available to chemists at the time. In 1869, the electromagnetic force fundamental to chemical interactions had only recently been identified; the modern idea of the atom was less than 70 years old; and another three decades were to elapse before scientists began uncovering the substructure of atoms that causes them to behave as they do. Despite these limitations in the knowledge available to Mendeleev, his original table was sound enough that it has never had to be discarded, but merely clarified and modified, in the years since he developed it. The rows of the periodic table of elements are called periods, and the columns are known as groups. Each box in the table represents an element by its chemical symbol, along with its atomic number and its average atomic mass in atomic mass units. Already a great deal has been said, and a number of terms need to be explained. These explanations will require the length of this essay, beginning with a little historical background, because chemists' understanding of the periodic table—and of the elements and atoms it represents—has evolved considerably since 1869. An element is a substance that cannot be broken down chemically into another substance. An atom is the smallest particle of an element that retains all the chemical and physical properties of the element, and elements contain only one kind of atom. The scientific concepts of both elements and atoms came to us from the ancient Greeks, who had a rather erroneous notion of the element and—for their time, at least—a highly advanced idea of the atom. Unfortunately, atomic theory died away in later centuries, while the mistaken notion of four "elements" (earth, air, fire, and water) survived virtually until the seventeenth century, an era that witnessed the birth of modern science. Yet the ancients did know of substances later classified as elements, even if they did not understand them as such. Among these were gold, tin, copper, silver, lead, and mercury. These, in fact, are such an old part of human history that their discoverers are unknown. The first individual credited with discovering an element was German chemist Hennig Brand (c. 1630-c. 1692), who discovered phosphorus in 1674. The work of English physicist and chemist Robert Boyle (1627-1691) greatly advanced scientific understanding of the elements. Boyle maintained that no substance was an element if it could be broken down into other substances: thus air, for instance, was not an element. Boyle's studies led to the identification of numerous elements in the years that followed, and his work influenced French chemists Antoine Lavoisier (1743-1794) and Joseph-Louis Proust (1754-1826), both of whom helped define an element in the modern sense. These men in turn influenced English chemist John Dalton (1766-1844), who reintroduced atomic theory to the language of science. In A New System of Chemical Philosophy (1808), Dalton put forward the idea that nature is composed of tiny particles, and in so doing he adopted the Greek word atomos to describe these basic units. Drawing on Proust's law of constant composition, Dalton recognized that the structure of atoms in a particular element or compound is uniform, but maintained that compounds are made up of compound "atoms." In fact, these compound atoms are really molecules, or groups of two or more atoms bonded to one another, a distinction clarified by Italian physicist Amedeo Avogadro (1776-1856). Dalton's and Avogadro's contemporary, Swedish chemist Jons Berzelius (1779-1848), developed a system of comparing the mass of various atoms in relation to the lightest one, hydrogen. Berzelius also introduced the system of chemical symbols—H for hydrogen, O for oxygen, and so on—in use today. Thus, by the middle of the nineteenth century, scientists understood vastly more about elements and atoms than they had just a few decades before, and the need for a system of organizing elements became increasingly clear. By mid-century, a number of chemists had attempted to create just such an organizational system, and though Mendeleev's was not the first, it proved the most useful. By the time Mendeleev constructed his periodic table in 1869, there were 63 known elements. At that point, he was working as a chemistry professor at the University of St. Petersburg, where he had become acutely aware of the need for a way of classifying the elements to make their relationships more understandable to his students. He therefore assembled a set of 63 cards, one for each element, on which he wrote a number of identifying characteristics for each. Along with the element symbol, discussed below, he included the atomic mass for the atoms of each. In Mendeleev's time, atomic mass was understood simply to be the collective mass of a unit of atoms—a unit developed by Avogadro, known as the mole—divided by Avogadro's number, the number of atoms or molecules in a mole. With the later discovery of subatomic particles, which in turn made possible the discovery of isotopes, figures for atomic mass were clarified, as will also be discussed. In addition, Mendeleev also included figures for specific gravity—the ratio between the density of an element and the density of water—as well as other known chemical characteristics of an element. Today, these items are typically no longer included on the periodic table, partly for considerations of space, but partly because chemists' much greater understanding of the properties of atoms makes it unnecessary to clutter the table with so much detail. Again, however, in Mendeleev's time there was no way of knowing about these factors. As far as chemists knew in 1869, an atom was an indivisible little pellet of matter that could not be characterized by terms any more detailed than its mass and the ways it interacted with atoms of other elements. Mendeleev therefore arranged his cards in order of atomic mass, then grouped elements that showed similar chemical properties. As Mendeleev observed, every eighth element on the chart exhibits similar characteristics, and thus, he established columns whereby element number x was placed above element number x + 8 —for instance, helium (2) above neon (10). The patterns he observed were so regular that for any "hole" in his table, he predicted that an element to fill that space would be discovered. Indeed, Mendeleev was so confident in the basic soundness of his organizational system that in some instances, he changed the figures for the atomic mass of certain elements because he was convinced they belonged elsewhere on the table. Later discoveries of isotopes, which in some cases affected the average atomic mass considerably, confirmed his suppositions. Likewise the undiscovered elements he named "eka-aluminum," "eka-boron," and "eka-silicon" were later identified as gallium, scandium, and germanium, respectively. Over a period of 35 years, between the discovery of the


From Yahoo Answers

Question:In my chemistry class, we did a distillation lab using wine. Here are my data. 1. Mass of wine = 7.09 g 2. Density of wine = 0.997 g/ml 3. Mass of distillate = 1.95 g 4. Density of distillate - 0.783 g/ml How do I calculate the percent ethanol of distillate? ONE MORE QUESTION: Does the density of distillate equal the density of ethanol?

Answers:_____ethanol distills at 95% (5% water) Density 0.789 g/cm , liquid (wikipedia) % ethanol in distillate = 100% * 0.789 g EtOH / cm3 / 0.783 g distillate / cm3 = ?? % 100.8 (hmmm! well, I guess you did better than theory - ETOH distills as water azeotrope!) I assume the Q was HOW MUCH ETHANOL is in the wine. so, if distillale is 100% EtOH, then % EtOH in wine = 100% * (1.95 g distillate / 0.783 g/ml) / (7,09 g wine / 0.997 g/ml) = ?? % (wow, is this ever a fortified wine!!) Most wines around 7-11% EtOH. SOLVE for % EtOH in wine

Question:In my chemistry class, we did a distillation lab using wine. Here are my data. 1. Mass of wine = 7.09 g 2. Density of wine = 0.997 g/ml 3. Mass of distillate = 1.95 g 4. Density of distillate - 0.783 g/ml How do I calculate the percent ethanol of distillate? ONE MORE QUESTION: Does the density of distillate equal the density of ethanol?

Answers:Here again _____ethanol distills at 95% (5% water) Density 0.789 g/cm , liquid (wikipedia) % ethanol in distillate = 100% * 0.789 g EtOH / cm3 / 0.783 g distillate / cm3 = ?? % 100.8 (hmmm! well, I guess you did better than theory - ETOH distills as water azeotrope!) I assume the Q was HOW MUCH ETHANOL is in the wine. so, if distillale is 100% EtOH, then % EtOH in wine = 100% * (1.95 g distillate / 0.783 g/ml) / (7,09 g wine / 0.997 g/ml) = ?? % (wow, is this ever a fortified wine!!) Most wines around 7-11% EtOH. SOLVE for % EtOH in wine

Question:Assuming that both liquids are at a temperature of 60 deg F and you have a hydrometer comparing the density of water what would that equal to the density of alcohol content. I'm trying to make a makeshift hydrometer and I'm basing it off of the density of water and then use math to add the rest of the increments.

Answers:Your question is confused. "what would that equal to the density of alcohol content" I can't make sense out of. Ethanol, which I assume is what you mean (there are other kinds of alcohols) has a density of about 800 kg/m while water has a density of about 1000 kg/m . The only mixture that would have a density equal to water would be pure water, or almost pure. .

Question:water is 1,2 g/ml ; density of ethanol is 0,789 g/ml)

Answers:mass ethanol = 10 mL x 0.789 = 7.89 g volume water = mass / d = 53 / 1.2 = 44.2 mL % by weight = mass ethanol / mass solution x 100 = = 7.89 /( 7.89 + 53) x 100 = 12.9 % % by volume = Vethanol / V solution x 100 = = 10 / (10 +44.2 )x100 = 18.4