chemistry_zone

Green chemistry

2008-10-26T00:41:00.000-07:00

Green chemistry, also called sustainable chemistry, is a chemical philosophy encouraging the design of products and processes that reduce or eliminate the use and generation of hazardous substances. Whereas environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature, green chemistry seeks to reduce and prevent pollution at its source. In 1990 the Pollution Prevention Act was passed in the United States. This act helped create a modus operandi for dealing with pollution in an original and innovative way. It aims to avoid problems before they happen.
As a chemical philosophy, green chemistry derives from organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and even physical chemistry. However, the philosophy of green chemistry tends to focus on industrial applications. Click chemistry is often cited as a style of chemical synthesis that is consistent with the goals of green chemistry. The focus is on minimizing the hazard and maximizing the efficiency of any chemical choice. It is distinct from environmental chemistry which focuses on chemical phenomena in the environment.
In 2005 Ryoji Noyori identified three key developments in green chemistry: use of supercritical carbon dioxide as green solvent, aqueous hydrogen peroxide for clean oxidations and the use of hydrogen in asymmetric synthesis.Examples of applied green chemistry are supercritical water oxidation, on water reactions and dry media reactions.

Radiochemistry

2008-10-26T00:35:00.000-07:00

Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being inactive as the isotopes are stable). Much of radiochemistry deals with the use of radioactivity to study ordinary chemical reactions.

Organic chemistry

2008-10-26T00:28:00.000-07:00

Organic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, the halogens as well as phosphorus, silicon and sulfur.
The original definition of "organic" chemistry came from the misconception that organic compounds were always related to life processes. However, organic molecules can be produced by processes not involving life. Life as we know it also depends on inorganic chemistry. For example, many enzymes rely on transition metals such as iron and copper; and materials such as shells, teeth and bones are part organic, part inorganic in composition. Apart from elemental carbon, only certain classes of carbon compounds (such as oxides, carbonates, and carbides) are conventionally considered inorganic. Biochemistry deals mainly with the natural chemistry of biomolecules such as proteins, nucleic acids, and sugars.
Because of their unique properties, multi-carbon compounds exhibit extremely large variety and the range of application of organic compounds is enormous. They form the basis of, or are important constituents of many products (paints, plastics, food, explosives, drugs, petrochemicals, to name but a few) and (apart from a very few exceptions) they form the basis of all earthly life processes.

Inorganic chemistry

2008-10-26T00:18:00.000-07:00

Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compound. This field covers all chemical compounds except the myriad organic compounds (compounds containing C-H bonds), which are the subjects of organic chemistry. The distinction between the two disciplines is far from absolute, and there is much overlap, most importantly in the sub-discipline of organometallic chemistry.

Medicinal Chemistry

2008-10-26T00:03:00.000-07:00

Medicinal or pharmaceutical chemistry is a scientific discipline at the intersection of chemistry and pharmacology involved with designing, shyntesyzing and developing pharmaceutical drugs. Medicinal chemistry involves the identification, synthesis and development of new chemical entities suitable for therapeutic use. It also includes the study of existing drugs, their biological properties, and their (QSAR). Pharmaceutical chemistry is focused on quality aspects of medicines and aims to assure fitness for the purpose of medicinal products.
Compounds used as medicines are overwhelmingly organic products. However, metal-containing compounds have been found to be useful as drugs. For example, the cis-platin series of platinum-containing complexes have found use as anti-cancer agents. This type of compounds are known as metal-based drugs.
Medicinal chemistry is a highly interdisciplinary science combining organic chemistry with biochemistry, computational chemistry, pharmacology, pharmacognosy, molecular biology, statistics, and physical chemistry.

Chemical engineering

2008-10-25T23:54:00.000-07:00

Chemical engineering is the branch of engineering that deals with the application of physical science, with mathematics, to the process of converting raw materials or chemicals into more useful or valuable forms. In addition to producing useful materials, chemical engineering is also concerned with pioneering valuable new materials and techniques, an important form of research and development. A person employed in this field is called a chemical engineer.
Chemical engineering largely involves the design and maintenance of chemical processes for large-scale manufacture. Chemical engineers in this branch are usually employed under the title of process engineer.

Geochemistry

2008-10-25T23:27:00.000-07:00

The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and their interaction with the hydrosphere and the atmosphere.

The most important fields of geochemistry are:

Isotope geochemistry: Determination of the relative and absolute concentrations of the elements and their isotopes in the earth and on earth's surface.
Examination of the distribution and movements of elements in different parts of the earth (crust, mantle, hydrosphere etc.) and in minerals with the goal to determine the underlying system of distribution and movement.
Cosmochemistry: Analysis of the distribution of elements and their isotopes in the cosmos.
Biogeochemistry: Field of study focusing on the effect of life on the chemistry of the earth.
Organic geochemistry: A study of the role of processes and compounds that are derived from living or once-living organisms.
Regional, environmental and exploration geochemistry: Applications to environmental, hydrological and mineral exploration studies.

Chemical reaction

2008-10-25T23:15:00.000-07:00

A chemical reaction is a process that always results in the interconversion of chemical substance. The substance or substances initially involved in a chemical reaction are called reactant. Chemical reactions are usually characterized by a chemical change, and they yield one or more products which are, in general, different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reaction.

Henry's Law

2008-10-25T23:08:00.001-07:00

A formula for Henry's Law is:

where:

is approximately 2.7182818, the base of the natural logarithm (also called Euler's number)

is the partial pressure of the solute above the solution

is the concentration of the solute in the solution (in one of its many units)

is the Henry's Law constant, which has units such as L·atm/mol, atm/(mol fraction) or Pa·m³/mol.

Taking the natural logarithm of the formula, gives us the more commonly used formula:

Some values for k include:

oxygen (O₂) : 769.2 L·atm/mol

carbon dioxide (CO₂) : 29.4 L·atm/mol

hydrogen (H₂) : 1282.1 L·atm/mol

when these gases are dissolved in water at 298 kelvin.

Note that in the above, the unit of concentration was chosen to be molarity. Hence the dimensional units: L is liters of solution, atm is the partial pressure of the gaseous solute above the solution (in atmospheres of absolute pressure), and mol is the moles of the gaseous solute in the solution. Also note that the Henry's Law constant, k, varies with the solvent and the temperature.

Raoult's law

2008-10-25T22:53:00.000-07:00

Established by Francois-Marie Raoults, Raoult's law states: the vapor presser of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution.

Once the components in the solution have reached chemical equilibrium , the total vapor pressure of the solution is:

and the individual vapor pressure for each component is

where

is the vapor pressure of the pure component

is the mole fraction of the component in solution

Consequently, as the number of components in a solution increases, the individual vapor pressures decrease, since the mole fraction of each component decreases with each additional component. If a pure solute which has zero vapor pressure (it will not evaporate) is dissolved in a solvent, the vapor pressure of the final solution will be lower than that of the pure solvent.

This law is strictly valid only under the assumption that the chemical interaction between the two liquids is equal to the bonding within the liquids: the conditions of an ideal solution. Therefore, comparing actual measured vapor pressures to predicted values from Raoult's law allows information about the relative strength of bonding between liquids to be obtained. If the measured value of vapor pressure is less than the predicted value, fewer molecules have left the solution than expected. This is put down to the strength of bonding between the liquids being greater than the bonding within the individual liquids, so fewer molecules have enough energy to leave the solution. Conversely, if the vapor pressure is greater than the predicted value more molecules have left the solution than expected, due to the bonding between the liquids being less strong than the bonding within each.

Atmospheric chemistry

2008-10-25T00:27:00.000-07:00

Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary field of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other areas of study such as climatology.

The composition and chemistry of the atmosphere is of importance for several reasons, but primarily because of the interactions between the atmosphere and living organisms. The composition of the Earth's atmosphere has been changed by human activity and some of these changes are harmful to human health, crops and ecosystems. Examples of problems which have been addressed by atmospheric chemistry include acid rain, photochemical smog and global warming. Atmospheric chemistry seeks to understand the causes of these problems, and by obtaining a theoretical understanding of them, allow possible solutions to be tested and the effects of changes in government policy evaluated

Photo Chemistry

2008-10-25T00:21:00.001-07:00

Photochemistry, a sub-discipline of chemistry, is the study of the interactions between atoms, small, and light (or electromagnetic radiation).

Physical chemistry

2008-10-24T23:58:00.000-07:00

Physical chemistry, is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems within the field of chemistry traditionally using the principles, practices and concepts of thermodynamics, quantum chemistry, statistical mechanic andn kinetics. It is mostly defined as a large field of chemistry, in which several sub-concepts are applied; the inclusion of quantum mechanic is used to illustrate the application of physical chemistry to atomic and particulate chemical interaction or experimentation.Physical chemistry is mostly referred to as a macromolecular doctrine, as the majority of the principles on which physical chemistry was founded are composed entirely of macromolecular concepts, such as colloids.

Biochemistry

2008-10-24T23:32:00.000-07:00

Biochemistry is the study of the chemical processes in living organisms. It deals with the structure and function of cellular components, such as proteins, carbohydrates, lipids,nucleic acids, and other biomolecules.

Although there are a vast number of different biomolecules, many are complex and large molecules (called polymers) that are composed of similar repeating subunits (called monomers). Each class of polymeric biomolecule has a different set of subunit types. For example, a protein is a polymer whose subunits are selected from a set of 20 or more amino acids. Biochemistry studies the chemical properties of important biological molecules, like proteins, in particular the chemistry of enzyme-catalyze reaction.
The biochemistry of cell metabolism and the endocrine system has been extensively described. Other areas of biochemistry include the genetic code (DNA,RNA), protein synthesis, cell membrane transport, and signal transduction.

Acidity and basicity

2008-10-24T23:08:00.000-07:00

A substance can often be classified as an acid or a base. This is often done on the basis of a particular kind of reaction, namely the exchange of protons between chemical compounds. However, an extension to this mode of classification was brewed up by the American chemist, Gilbert Newton Lewis; in this mode of classification the reaction is not limited to those occurring in an aqueous solution, thus is no longer limited to solutions in water. According to concept as per Lewis, the crucial things being exchanged are charges. There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept.

Mole

2008-10-24T23:00:00.000-07:00

A mole is the amount of a substance that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state.This number is known as the Avogadro constan, and is determined empirically. The currently accepted value is 6.02214179(30)×10²³ mol^-1. It is much like the term "a dozen" in that it is an absolute number (having no units) and can describe any type of elementary object, although the mole's use is usually limited to measurement of subatomic, atomic, and molecular structures.
The number of moles of a substance in one liter of a solution is known as its molarity. Molarity is the common unit used to express the concentration of a solution in physical chemistry.

Atom

2008-10-24T22:54:00.000-07:00

The atom is the smallest unit of an element that retains the chemical properties of that element. An atom has an electron cloud consisting of negatively charged electrons surrounding a dense nucleus. The nucleus contains positively charged protons and electrically neutral neutrons. When the number of protons in the nucleus equals the number of electrons, the atom is electrically neutral; otherwise it is an ion and has a net positive or negative charge. An atom is classified according to its number of protons and neutrons: the number isotope of protons determines the chemical element and the number of neutrons determines the of that element.

Hess's law

2008-10-21T00:55:00.000-07:00

Hess's law is a law of physical chemistry named for Germain Hess's expansion of the Hess Cycle and used to predict the enthalpy change and conservation of energy (denoted as state function ΔH) regardless of the path through which it is to be determined.

The law states that because enthalpy is a state function, the enthalpy change of a reaction is the same regardless of what pathway is taken to achieve the products. In other words, only the start and end states matter to the reaction, not the individual steps between.

"The total energy change for a chemical reaction is independent of the route by which the reaction takes place, provided initial and final conditions are the same."

Periodic Table

2008-10-21T00:28:00.000-07:00

Molecule

2008-10-21T00:07:00.000-07:00

In chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. It can also be defined as a unit of two or more atoms held together by covalent bonds.In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules and biomolecules. Molecules are distinguished from polyatomic ion in this strict sense.

Ion

2008-10-20T23:45:00.000-07:00

An ion is an atom or molecule which has lost or gained one or more valence electron, giving it a positive or negative electrical charge.

A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion. Conversely, a positively-charged ion, which has fewer electrons than protons, is known as a cation.

An ion consisting of a single atom is called a monoatomic ion, but if it consists of two or more atoms, it is a polyatomic ion. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions.

Ions are denoted in the same way as electrically neutral atoms and molecules except for the presence of a superscript indicating the sign of the net electric charge and the number of electrons lost or gained, if more than one.

2008-10-11T21:01:00.000-07:00