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Chemical affinity

In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of an atom or compound to combine by chemical reaction with atoms or compounds of unlike composition.

According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Reactions by Gilbert N. Lewis and Merle Randall led to the replacement of the term "affinity" by the term "free energy" in much of the English-speaking world.

## Modern conceptions

In modern terms, we relate affinity to the phenomenon whereby certain atoms or molecules have the tendency to aggregate or bond. For example, in the 1919 book Chemistry of Human Life physician George W. Carey states that, "Health depends on a proper amount of iron phosphate Fe3(PO4)2 in the blood, for the molecules of this salt have chemical affinity for oxygen and carry it to all parts of the organism." In this antiquated context, chemical affinity is sometimes found synonymous with the term "magnetic attraction". Many writings, up until about 1925, also refer to a "law of chemical affinity".

## Thermodynamics

In 1923, the Belgian mathematician and physicist ThÃ©ophile de Donder derived a relation between affinity A and the Gibbs free energyG of a chemical reaction. Through a series of derivations, de Donder showed that if we consider a mixture of chemical species with the possibility of chemical reaction, it can be proven that the following relation holds:

A = -\Delta_rG \,

With the writings of ThÃ©ophile de Donder as precedent, Ilya Prigogine and Defay in Chemical Thermodynamics (1954) defined chemical affinity (denoted by A) as a function of the increments in uncompensated heat of reaction and reaction progress variable (denoted by dQ' and dÎ¾, respectively):

A = \frac{dQ'}{d \xi}. \,

This definition is useful for quantifying the factors responsible both for the state of equilibrium systems (where ), and for changes of state of non-equilibrium systems (where ).

The present IUPAC definition is that affinity is the negative partial derivative of Gibbs energy with respect to extent of reaction at constant pressure and temperature. That is,

A = -\left(\frac{\partial G}{\partial \xi}\right)_{P,T}.

It follows that affinity is positive for spontaneous reactions.

## History

"Chemical affinity", historically, refers to the "force" that causes chemical reactions. A broad definition, used generally throughout history, is that chemical affinity is that whereby substances enter into or resist decomposition. In current use, it

Ilya Prigogine summarized the concept of affinity, saying, "All chemical reactions drive the system to a state of equilibrium in which the affinities of the reactions vanish."

The term affinity has been used figuratively since c. 1600 in discussions of structural relationships in chemistry, philology, etc., and reference to "natural attraction" is from 1616.

The idea of affinity is extremely old. Many attempts have been made at identifying its origins. The majority of such attempts, however, except in a general manner, end in futility since "affinities" lie at the basis of all magic, thereby pre-dating science. Physical chemistry, however, was one of the first branches of science to study and formulate a "theory of affinity". The name affinitas was first used in the sense of chemical relation by German philosopher Albertus Magnus near the year 1250. Later, those as Robert Boyle, John Mayow, Johann Glauber, Isaac Newton, and Georg Stahl put forward ideas on elective affinity in attempts to explain how heat is evolved during combustion reactions.

The modern term chemical affinity is a somewhat modified variation of its eighteenth-century precursor "elective affinity" or elective attractions, a coinage of the Swedish chemist Torbern Olof Bergman from his book De attractionibus electivis (1775). Antoine Lavoisier, in his famed 1789 TraitÃ© Ã‰lÃ©mentaire de Chimie (Elements of Chemistry), refers to Bergmannâ€™s work and discusses the concept of elective affinities or attractions.

Goethe used the concept in his novel Elective Affinities, (1809)

### Geoffroy's 1718 affinity table

The first-ever affinity table, which was based on displacement reactions, was published in 1718 by the French chemist Ã‰tienne FranÃ§ois Geoffroy. Geoffroy's name is best known in connection with these tables of "affinities" (tables des rapports), which were first present

Integrated gasification combined cycle

An integrated gasification combined cycle (IGCC) is a technology that turns coal into gasâ€”synthesis gas (syngas). It then removes impurities from the coal gas before it is combusted and attempts to turn any pollutants into re-usable byproducts. This results in lower emissions of sulfur dioxide, particulates and mercury. Excess heat from the primary combustion and generation is then passed to a steam cycle, similarly to a combined cycle gas turbine. This then also results in improved efficiency compared to conventional pulverized coal.

## Significance

Both because it can be found in abundance in America and many other countries and because the price of it has remained relatively constant in recent years, coal is used for about 50 percent of U.S. electricity needs. Thus the lower emissions that IGCC technology allows may be important in the future as emission regulations tighten due to growing concern for the impacts of pollutants on the environment and the globe.

## Operations

Below is a schematic flow diagram of an IGCC plant:

The gasification process can produce syngas from high-sulfur coal, heavy petroleum residues and biomass.

The plant is called integrated because its syngas is produced in a gasification unit in the plant which has been optimized for the plant's combined cycle. In this example the syngas produced is used as fuel in a gas turbine which produces electrical power. To improve the overall process efficiency heat is recovered from both the gasification process and also the gas turbine exhaust in 'Waste Heat Boilers' producing steam. This steam is then used in steam turbines to produce additional electrical power.

## Installations

In 2007 there were only two IGCC plants generating power in the U.S.; however, several new IGCC plants are expected to come online in the U.S. in the 2012-2020 time frame. The [http://www.fossil.energy.gov/programs/powersystems/cleancoal/ DOE Clean Coal] Demonstration Project helped construct 3 IGCC plants: Wabash River Power Station in West Terre Haute, Indiana, Polk Power Station in Tampa, Florida (online 1996), and Pinon Pine in Reno, Nevada. In the Reno demonstration project, researchers found that then-current IGCC technology would not work more than 300 feet (100m) above sea level. The DOE report in reference 3 however makes no mention of any altitude effect, and most of the problems were associated with the solid waste extraction system. The plant failed.

Poland's KÄ™dzierzyn will soon host a Zero-Emission Power & Chemical Plant that combines coal gasification technology with Carbon Capture & Storage (CCS). The supplement of up to 10% biomass in the combustion process will make this plant even more environmentally-friendly.

The first generation of IGCC plants polluted less than contemporary coal-based technology, but also polluted water; for example, the Wabash River Plant was out of compliance with its water permit during 1998â€“2001 because it emitted arsenic, selenium and cyanide. The Wabash River Generating Station is now wholly owned and operated by the Wabash River Power Association.

IGCC is now touted as capture ready and could potentially capture and store carbon dioxide. (See FutureGen)

There are several advantages and disadvantages when compared to conventional post combustion carbon capture and various variations and these are fully discussed at.

## Cost and reliability

The main problem for IGCC is its extremely high capital cost, upwards of $3,593/kW. Official US government figures give more optimistic estimates of$1,491/kW installed capacity (2005 dollars) v. $1,290 for a conventional clean coal facility, but in light of current applications, these cost estimates have been demonstrated to be incorrect. Outdated per megawatt-hour cost of an IGCC plant vs a pulverized coal plant coming online in 2010 would be$56 vs $52, and it is claimed that IGCC becomes even more attractive when you include the costs of carbon capture and sequestration, IGCC becoming$79 per megawatt-hour vs. $95 per megawatt-hour for pulverized coal. Recent testimony in regulatory proceedings show the cost of IGCC to be twice that predicted by Goddell, from$96 to 104/MWhr. That's before addition of carbon capture and sequestration (sequestration has been a mature technology at both Weyburn in the US (for enhanced oil recovery) and Sleipner in the North Sea at a commercial scale for the past ten years)â€”capture at a 90% rate is expected to have a \$30/MWh additional cost.

Wabash River was down repeatedly for long stretches due to gasifier problems, and the gasifier problems have not been remediedâ€”subsequent projects, such as Excelsior's Mesaba Project, have a third gasifier and train built in. However, the past year has seen Wabash River running reliably, with availability comparable to or better than other technologies.

The Polk County IGCC has design problems. First, the project was initially shut down because of corrosion in the slurry pipeline that fed slurried coal from the rail cars into the gasifier. A new coating for the pipe was developed. Second, the thermocoupler was replaced in less than two years; an indication that the gasifier had problems with a variety of feedstocks; from bituminous to sub-bituminous coal. The gasifer was designed to also handle lower rank lignites. Third, unplanned down time on the gasifer because of refractory liner problems, and those problems were expensive to repair. The gasifer design was originally done in Italy for a gasifier smaller by 2 x what was built at Polk. Newer ceramic materials may assist in improving gasifier performance and longevity. Understanding the operating problems of the built IGCC is necessary to design the IGCC of the future. (Polk IGCC Power Plant, http://www.clean-energy.us/projects/polk_florida.html.) Keim, K., 2009, IGCC A Project on Sustainability Management Systmes for Plant Re-Design and Re-Image. Unpublished paper; Harvard University)

General Electric is currently designing an IGCC model plant that should introduce greater reliability. GE's model features advanced turbines optimized for the coal syngas. Eastman's industrial gasification plant in Kingsport, TN uses a GE Energy solid-fed gasifier. Eastman, a fortune 500 company, built the facility in 1983 without any state or federal subsidies and turns a profit.

There are several refinery-based IGCC plants in Europe that have demonstrated good availability (90-95%) after initial shakedown periods. Several factors help this performance:

1. None of these facilities use advanced technology (F type) gas turbines.
2. All refinery-based plants use refinery residues, rather than coal, as the feedstock. This eliminates coal handling and coal preparation equipment and its problems. Also, there is a much lower level of ash produced in the gasifier, which reduces cleanup and downtime in its gas cooling and cleaning stages.
3. These non-utility p

Chemical change

In a chemical change, bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another. Some exothermic reactions may be hot enough to cause certain chemicals to also undergo a change in state; for example in the case of aqueous solutions, bubbles may not necessarily be newly produced gas but instead water vapor.

Whenever chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. An example of a chemical change is the reaction between sodium hydroxide and hydrogen chloride to produce sodium chloride, or table salt. This reaction is so exothermic, meaning it releases heat in the form of energy, that even flames are generated. This is an example of a chemical change because the end product is molecularly different from the starting molecules.

Chemical changes are happening all the time. There are several different types of chemical change, including: synthesis, decomposition, single displacement, double displacement, neutralization, precipitation, combustion and redox.

## Examples of chemical changes

A primary example of chemical change is the combustion of methane to produce carbon dioxide and water.

Other examples of chemical changes are:

Evidence of a chemical change:

The following can indicate that a chemical change took place, although this evidence is not conclusive:

• Change of odor
• Change of color (for example, silver to reddish-brown when iron rusts).
• Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat.
• Change of form (for example, burning paper).
• Light, heat, or sound is given off.
• Formation of gases, often appearing as bubbles.
• Formation of precipitate (insoluble particles).
• The decomposition of organic matter (for example, rotting food).

A chemical change can have a huge impact on a physical change.

## Laws of chemical changes

Chemical law

Chemical property

A chemical property is any of a material's properties that becomes evident during a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected for its chemical properties to be investigated.

Chemical properties can be contrasted with physical properties, which can be discerned without changing the substance's structure. However, for many properties within the scope of physical chemistry, and other disciplines at the border of chemistry and physics, the distinction may be a matter of researcher's perspective. Material properties, both physical and chemical, can be viewed as supervenient; i.e., secondary to the underlying reality. Several layers of superveniency are possible.

Chemical properties can be used for building chemical classifications.

## Examples of chemical properties

For example hydrogen has the potential to ignite and explode given the right conditions. This is a chemical property.

Metals in general do they have chemical properties of reaction with an acid. Zinc reacts with hydrochloric acid to produce hydrogen gas. This is a chemical property.

Question:I combined Hydrochloric Acid and Bromothymol Blue in a lab, and observed it created a yellow solution. Was the colour change be a result of a chemical reaction, or not?

Answers:No, that was a physical change. A chemical change is when it gives off light, heat, gas, bubbles, precipitate, etc.