A burette, an apparatus for carrying out acid-base titration, is an important part of equilibrium chemistry.

In a chemical process, chemical equilibrium is the state in which the chemical activities or concentrations of the reactants and products have no net change over time. Usually, this would be the state that results when the forward chemical process proceeds at the same rate as their reverse reaction. The reaction rates of the forward and reverse reactions are generally not zero but, being equal, there are no net changes in any of the reactant or product concentrations. This process is known as dynamic equilibrium ^{[1] [2]} Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... diagram of modern burette A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. ... This article is about volumetric titration. ... In a scientific sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. ... Activity in chemistry is a measure of how different molecules in a non-ideal gas or solution interact with each other. ... This page refers to concentration in the chemical sense. ... In a scientific sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. ... A reversible reaction is a chemical reaction that may proceed in both the forward and reverse directions. ... Iron rusting - a chemical reaction with a slow reaction rate. ... A dynamic equilibrium occurs when two reversible processes occur at the same rate. ...

The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate... The binding constant is a special case of the equilibrium constant K. The equilibrium state of molecular binding, i. ... In chemistry and biochemistry, a dissociation constant or an ionization constant is a specific type of equilibrium constant used for reversible reactions or processes. ... A partition coefficient is a measure of differential solubility of a compound in two solvents. ... Relative volatility is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals. ... In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction. ... In biochemistry, equilibrium unfolding is the process of unfolding a protein or RNA molecule by gradually changing its solution conditions, i. ... A theoretical plate in separation processes is a hypothetical zone in which two phases establish an equilibrium, also referred to as an equilibrium stage or a theoretical tray. ... Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their solution preferences for two different immiscible liquids, usually water and an organic solvent. ... In physical chemistry, mineralogy, and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. ... It has been suggested that this article or section be merged with Gibbs phase rule. ... In a chemical reaction with certain initial concentrations of reactants and products, it is useful to know if the reaction will shift to the right (increasing the concentrations of the products) or if it will shift to the left (increasing the concentrations of the reactants). ... Relative volatility is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals. ... It has been suggested that this article or section be merged with chemical equilibrium. ... Stability constants, formation constants, binding constants, association constants and dissociation constants are all types of equilibrium constant. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ... A theoretical plate in separation processes is a hypothetical zone in which two phases establish an equilibrium, also referred to as an equilibrium stage or a theoretical tray. ... Vapor-liquid equilibrium, abbreviated as VLE by some, is a condition where a liquid and its vapor (gas phase) are in equilibrium with each other, a condition or state where the rate of evaporation (liquid changing to vapor) equals the rate of condensation (vapor changing to liquid) on a molecular...

Introduction

In a chemical reaction, when reactants are mixed together in a reaction vessel (and heated if needed), the whole of reactants do not get converted into the products. After some time (which may be shorter than millionths of a second or longer than the age of the universe), there will come a point when a fixed amount of reactants will exist in harmony with a fixed amount of products, the amounts of neither changing anymore. This is called chemical equilibrium. For other uses, see Chemical reaction (disambiguation). ...

The concept of chemical equilibrium was developed after Berthollet (1803) found that some chemical reactions are reversible. For any reaction such as Claude Louis Berthollet Claude Louis Berthollet (December 9, 1748 – November 6, 1822) was a French chemist. ... For other uses, see Chemical reaction (disambiguation). ... A reversible reaction is a chemical reaction that may proceed in both the forward and reverse directions. ...

to be at equilibrium the rates of the forward and backward (reverse) reactions have to be equal. In this chemical equation with harpoon arrows pointing both ways to indicate equilibrium, A and B are reactant chemical species, S and T are product species, and α, β, σ, and τ are the stoichiometric coefficients of the respective reactants and products. The equilibrium position of a reaction is said to lie far to the right if, at equilibrium, nearly all the reactants are used up and far to the left if hardly any product is formed from the reactants. Iron rusting - a chemical reaction with a slow reaction rate. ... A chemical equation is a symbolic representation of a chemical reaction. ... A reactant or reagent is any substance initially present in a chemical reaction. ... Look up alfa, alpha in Wiktionary, the free dictionary. ... Beta is the second letter of the Greek alphabet (β). Beta may also refer to: In mathematics, statistics, and economics: Beta function in mathematics Beta distribution in statistics Beta coefficient in finance Standardized coefficient in statistics, also sometimes known as beta coefficient In physics: Beta-function in quantum field theory Beta... For other uses, see Sigma (disambiguation). ... Look up Τ, Ï„ in Wiktionary, the free dictionary. ... In a chemical reaction system the stoichiometric coefficient of the i-th component is defined as or where Ni is the number of molecules of i and ξ is the progress variable or extent of reaction. ...

Guldberg and Waage (1865), building on Berthollet’s ideas, proposed the law of mass action: Cato Maximilian Guldberg (born August 11, 1836 in Christiania (today Oslo); died January 14, 1902 in Oslo) was a norwegian mathematician and chemist. ... Peter Waage (June 29, 1833 - January 13, 1900) was a significant Norwegian chemist. ... Mass action in science is the idea that a large number of small units (especially atoms or molecules) acting randomly by themselves can in fact have a larger pattern. ...

where A, B, S and T are active masses and k₊ and k₋ are rate constants. Since forward and backward rates are equal: Activity in chemistry is a measure of how different molecules in a non-ideal gas or solution interact with each other. ... In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction. ...

and the ratio of the rate constants is also a constant, now known as an equilibrium constant. In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction. ...

By convention the products form the numerator. Unfortunately, the law of mass action is valid only for concerted one-step reactions that proceed through a single transition state and is not valid in general because rate equations do not in general follow the stoichiometry of the reaction as Guldberg and Waage had proposed (see, for example, nucleophilic aliphatic substitution by SN1 or reaction of hydrogen and bromine to form hydrogen bromide). Equality of forward and backward reaction rates, however, is a necessary condition for chemical equilibrium, though it is not sufficient to explain why equilibrium occurs. In algebra, a vulgar fraction consists of one integer divided by a non-zero integer. ... The Law of Mass Action, first expressed by Waage and Guldberg in 1864 [1], states (in modern language) that the rate of a chemical reaction is proportional to probability that the reacting molecules will be found together in a small volume. ... The transition state of a chemical reaction is a particular configuration along the reaction coordinate. ... Iron rusting - a chemical reaction with a slow reaction rate. ... Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry) is the calculation of quantitative (measurable) relationships of the reactants and products in chemical reactions (chemical equations). ... In chemistry, nucleophilic substitution is a class of substitution reaction in which an electron-rich nucleophile attacks a molecule and replaces a group or atom, called the leaving group. ... This article is about the chemistry of hydrogen. ... Bromo redirects here. ... Flash point Non flammable Supplementary data page Structure and properties n, εr, etc. ... This article discusses only the formal meanings of necessary and sufficient causal meanings see causation. ... This article discusses only the formal meanings of necessary and sufficient causal meanings see causation. ...

Despite the failure of this derivation, the equilibrium constant for a reaction is indeed a constant, independent of the activities of the various species involved, though it does depend on temperature as observed by the van 't Hoff equation. Adding a catalyst will affect both the forward reaction and the reverse reaction in the same way and will not have an effect on the equilibrium constant. The catalyst will speed up both reactions thereby increasing the speed at which equilibrium is reached ^{[3] [4]}. The van t Hoff equation in chemical thermodynamics relates the change in temperature (T) to the change in the equilibrium constant (K) given the enthalpy change (ΔH). ... It has been suggested that this article or section be merged into Catalysis. ...

Although the macroscopic equilibrium concentrations are constant in time reactions do occur at the molecular level. For example, in the case of ethanoic acid dissolved in water and forming ethanoate and hydronium ions, The chemical compound acetic acid (from the Latin word acetum, meaning vinegar), systematically called ethanoic acid, is the acid that gives vinegar its sour taste. ... Acetate, or ethanoate, is the anion of a salt or ester of acetic acid. ... In chemistry, hydronium is the common name for the cation H3O+ derived from protonation of water. ...

CH₃CO₂H + H₂O ⇌ CH₃CO₂⁻ + H₃O⁺

a proton may hop from one molecule of ethanoic acid on to a water molecule and then on to an ethanoate ion to form another molecule of ethanoic acid and leaving the number of ethanoic acid molecules unchanged. This is an example of dynamic equilibrium. Equilibriums, like the rest of thermodynamics, are statistical phenomena, averages of microscopic behaviour. A dynamic equilibrium occurs when two reversible processes occur at the same rate. ...

Le Chatelier's principle (1884) is a useful principle that gives a qualitative idea of an equilibrium system's response to changes in reaction conditions. If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. For example, adding more S from the outside will cause an excess of products and the system will try to counteract this by increasing the reverse reaction and pushing the equilibrium point backward (though the equilibrium constant will stay the same). In chemistry, Le Chateliers principle, also called the Le Chatelier-Braun principle, can be used to predict the effect of a change in conditions on a chemical equilibrium. ...

If mineral acid is added to the ethanoic acid mixture, increasing the concentration of hydronium ion, the amount of dissociation must decrease as the reaction is driven to the left in accordance with this principle. This can also be deduced from the equilibrium constant expression for the reaction: Headline text Happy Hannukah and a happy new year!! POOP e Butt ...

if {H₃O⁺} increases {CH₃CO₂H} must increase and {CH₃CO₂⁻} must decrease.

A quantitative version is given by the reaction quotient. In a chemical reaction with certain initial concentrations of reactants and products, it is useful to know if the reaction will shift to the right (increasing the concentrations of the products) or if it will shift to the left (increasing the concentrations of the reactants). ...

J.W. Gibbs suggested in 1873 that equilibrium is attained when the Gibbs energy of the system is at its minimum value (assuming the reaction is carried out under constant pressure). What this means is, the derivative of the Gibbs energy with respect to reaction coordinate (a measure of the extent of reaction that has occurred, ranging from zero for all reactants to a maximum for all products) vanishes, signalling a stationary point. This derivative is usually called, for certain technical reasons, the Gibbs energy change^[5]. This criterion is both necessary and sufficient. If a mixture is not at equilibrium the liberation of the excess Gibbs energy (or Helmholtz energy at constant volume reactions) is the “driving force” for the composition of the mixture to change until equilibrium is reached. The equilibrium constant can be related to the standard Gibbs energy change for the reaction by the equation Josiah Willard Gibbs (February 11, 1839 – April 28, 1903) was an American physical chemist. ... In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist Willard Gibbs, which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given proportions may be considered a... In chemistry, a reaction coordinate is an abstract one-dimensional coordinate system which represents progress along a reaction pathway. ... In a chemical reaction system the stoichiometric coefficient of the i–th component is defined as or where Ni is the number of molecules of i, and ξ is the progress variable or extent of reaction (Prigogine & Defay, p. ... Stationary points (red pluses) and inflection points (green circles). ... It has been suggested that this article or section be merged into Helmholtz energy. ... In thermodynamics, the Gibbs energy or Gibbs energy function is the energy portion of a thermodynamic system available to do work. ...

where R is the universal gas constant and T the temperature. Molar gas constant (also known as universal gas constant, usually denoted by symbol R) is the constant occurring in the universal gas equation, i. ... For other uses, see Temperature (disambiguation). ...

When the reactants are dissolved in a medium of high ionic strength the quotient of activity coefficients may be taken to be constant. In that case the concentration quotient, K_c, Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ... The ionic strength of a solution is a function of the concentration of all ions present in a solution. ... The Activity coefficient for chemicals in a mixture is an indicator of what the concentration of that chemical will be in a vapor of the mixture. ...

where [A] is the concentration of A, etc., is independent of the analytical concentration of the reactants. For this reason, equilibrium constants for solutions are usually determined in media of high ionic strength. K_c varies with ionic strength, temperature and pressure (or volume). Likewise K_p for gases depends on partial pressure. These constants are easier to measure and encountered in high-school chemistry courses. For other uses, see Concentration (disambiguation). ... Analytical concentration is the concentration of a substance dumped into a solution. ... Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ... Equilibrium constants are determined in order to quantify chemical equilibria. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ...

Thermodynamics

The relationship between the Gibbs energy and the equilibrium constant can be found by considering chemical potentials. The thermodynamic condition for chemical equilibrium is^[6] In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ...

• At constant pressure ΔG=0 (ΔG is the change Gibbs free energy for the reaction)
• At constant volume ΔA=0 (ΔA is the change in Helmholtz free energy for the reaction)

In this article only the constant pressure case is considered. The constant volume case is important in geochemistry and atmospheric chemistry where pressure variations are significant. Note that if reactants and products were in standard state (completely pure) then there would be no reversibility and no equilibrium. The mixing of the products and reactants contributes a large entropy (known as entropy of mixing) to states containing equal mixture of products and reactants. The combination of the standard Gibbs energy change and the Gibbs energy of mixing determines the equilibrium state.^[7] In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... In thermodynamics, the Helmholtz free energy is a thermodynamic potential which measures the “useful” work obtainable from a closed thermodynamic system at a constant temperature. ... 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 Earths chemical components in time and space, and their interaction with... Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earths atmosphere and that of other planets is studied. ... In thermodynamics the Entropy of mixing is the entropy change when two different gases or two solvents mix or even when a solute is dissolved in a solvent. ...

In general an equilibrium system is defined by writing an equilibrium equation for the reaction

To meet the thermodynamic condition for equilibrium the Gibbs energy must be stationary, meaning that the derivative of G with respect to reaction coordinate (ΔG) must be zero. It can be shown that ΔG is in fact equal to the difference between the chemical potentials of the products and those of the reactants. Therefore, the sum of the Gibbs energies of the reactants must be the equal to the sum of the Gibbs energies of the products. In chemistry, a reaction coordinate is an abstract one-dimensional coordinate system which represents progress along a reaction pathway. ... In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist Willard Gibbs, which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given proportions may be considered a...

where μ is in this case a partial molar Gibbs energy, a chemical potential. The chemical potential of a reagent A is a function of the activity, {A} of that reagent. Look up Îœ, μ in Wiktionary, the free dictionary. ... In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist Willard Gibbs, which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given proportions may be considered a... Activity in chemistry is a measure of how different molecules in a non-ideal gas or solution interact with each other. ...

Substituting expressions like this into the Gibbs energy equation: In thermodynamics, the Gibbs energy or Gibbs energy function is the energy portion of a thermodynamic system available to do work. ...

which at constant pressure and temperature becomes:

results in:

By substituting the chemical potentials:

the relationship becomes:

At equilibrium and therefore

leading to:

ΔG_m^O is the standard molar Gibbs energy change for the reaction and K is the equilibrium constant. Note that activities and equilibrium constants are dimensionless numbers. In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction. ...

Treatment of activity

The expression for the equilibrium constant can be re-written as the product of a concentration quotient, K_c and an activity coefficient quotient, Γ. The Activity coefficient for chemicals in a mixture is an indicator of what the concentration of that chemical will be in a vapor of the mixture. ...

[A] is the concentration of reagent A etc. It is possible in principle to obtain values of the activity coefficients, γ. For solutions equations such as the Debye-Hückel equation or extensions such as Davies equation^[8] or Pitzer equations^[9] may be used.^{Software (below)}. However this is not always possible. It is common practice to assume that Γ is a constant and to use the concentration quotient in place of the thermodynamic equilibrium constant. It is also general practice to use the term equilibrium constant instead of the more pedantically accurate concentration quotient. This practice will be followed here. The Debye-Hückel equation, named for its developers Peter Debye and Erich Hückel, provides one way to obtain activity coefficients . ...

For reactions in the gas phase partial pressure is used in place of concentration and fugacity coefficient in place of activity coefficient. In the real world, for example when making ammonia industrially, fugacity coefficients must be taken into account. Fugacity, f, is the product of partial pressure and fugacity coefficient. The chemical potential of a species in the gas phase is given by In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... In thermodynamics, the fugacity is a state function of any isothermal system. ... The Haber Process (also known as Haber–Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ...

so the general expression defining an equilibrium constant is valid for both solution and gas phases.

Justification for the use of concentration quotients

In aqueous solution, equilibrium constants are usually determined in the presence of an "inert" electrolyte such as sodium nitrate NaNO₃ or Potassium perchlorate KClO₄. The ionic strength, I, of a solution containing a dissolved salt, X⁺Y^-, is given by Made of Porn and sex things Inhalation respiratory irritation Skin May cause irritation. ... Potassium perchlorate, chemical formula KClO4, is a strong oxidizer. ... The ionic strength of a solution is a function of the concentration of all ions present in a solution. ...

where c stands for concentration, z stands for ionic charge and the sum is taken over all the species in equilibrium. When the concentration of dissolved salt is much higher than the analytical concentrations of the reagents, the ionic strength is effectively constant. Since activity coefficients depend on ionic strength the activity coefficients of the species are effectively independent of concentration. Thus, the assumption that Γ is constant is justified. The concentration quotient is a simple multiple of the equilibrium constant.^[10] Gamma (uppercase Γ, lowercase γ) is the third letter of the Greek alphabet. ...

However, K_c will vary with ionic strength. If it is measured at a series of different ionic strengths the value can be extrapolated to zero ionic strength.^[9] The concentration quotient obtained in this manner is known, paradoxically, as a thermodynamic equilibrium constant.

To use a published value of an equilibrium constant in conditions of ionic strength different from the conditions used in its determination, the value should be adjusted^{Software (below)}.

Metastable mixtures

A mixture may be appear to have no tendency to change, though it is not at equilibrium. For example, a mixture of SO₂ and O₂ is metastable as there is a kinetic barrier to formation of the product, SO₃. Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Metastability is the ability of a non-equilibrium state to persist for a long period of time. ... The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ... “SO3” redirects here. ...

2SO₂ + O₂ 2SO₃

The barrier can be overcome when a catalyst is also present in the mixture as in the Contact process, but the catalyst does not affect the equilibrium concentrations. Catalyst redirects here. ... This article or section does not cite its references or sources. ...

Likewise, the formation of bicarbonate from carbon dioxide and water is very slow under normal conditions For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...

CO₂ + 2H₂O HCO₃^- +H₃O⁺

but almost instantaneous in the presence of the catalytic enzyme carbonic anhydrase. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Carbonic anhydrase (carbonate dehydratase) is a family of metalloenzymes (enzymes that contain one or more metal atoms as a functional component of the enzyme) that catalyze the rapid interconversion of carbon dioxide and water into carbonic acid, protons, and bicarbonate ions. ...

Pure compounds in equilibria

When pure substances (liquids or solids) are involved in equilibria they do not appear in the equilibrium equation ^[11]

Applying the general formula for an equilibrium constant to the specific case of ethanoic acid one obtains

It may be assumed that the concentration of water is constant. This assumption will be valid for all but very concentrated solutions. The equilibrium constant expression is therefore usually written as

where now

a constant factor is incorporated into the equilibrium constant.

A particular case is the self-ionization of water itself The self-ionization of water is the chemical reaction in which two water molecules react to produce a hydronium (H3O+) and a hydroxide ion (OH-): The reaction is also known as the autoionization or autodissociation of water. ...

The self-ionization constant of water is defined as

It is perfectly legitimate to write [H⁺] for the hydronium ion concentration since the state of solvation of the proton is constant (in dilute solutions) and so does not affect the equilibrium concentrations. K_w varies with variation in ionic strength and/or temperature. In chemistry, hydronium is the common name for the cation H3O+. // Nomenclature According to IUPAC ion nomenclature, it should be referred to as oxonium. ... Solvation is the attraction and association of molecules of a solvent with molecules or ions of a solute. ...

The concentrations of H⁺ and OH^- are not independent quantities. Most commonly [OH^-] is replaced by K_w[H⁺]^-1 in equilibrium constant expressions which would otherwise hydroxide. Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ...

Solids also do not appear in the equilibrium equation. An example is the Boudouard reaction ^[11]: Boudouard reaction is the redox reaction of chemical equilibrium mixture of carbon monoxide and carbon dioxide in a given temperature. ...

for which the equation (without solid carbon) is written as:

Multiple equilibria

Consider the case of a dibasic acid H₂A. When dissolved in water the mixture will contain H₂A, HA^- and A^2-. This equilibrium can be split into two steps in each of which one proton is liberated.

K₁ and K₂ are examples of stepwise equilibrium constants. The overall equilibrium constant,β_D, is product of the stepwise constants.

Note that these constants are dissociation constants because the products on the right hand side of the equilibrium expression are dissociation products. In many systems it is preferable to use association constants. The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate...

β₁ and β₂ are examples of association constants. Clearly β₁ = 1/K₂ and β₂ = 1/β_D; lg β₁ = pK₂ and lg β₂ = pK₂ + pK₁^[12]

Effect of temperature change on an equilibrium constant

The effect of changing temperature on an equilibrium constant is given by the van 't Hoff equation The van t Hoff equation in chemical thermodynamics relates the change in temperature (T) to the change in the equilibrium constant (K) given the enthalpy change (ΔH). ...

Thus, for exothermic reactions, (ΔH is negative) K decreases with temperature, but for endothermic reactions (ΔH is positive) K increases with temperature. An alternative formulation is In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat. ... In thermodynamics, the word endothermic describes a process or reaction that absorbs energy in the form of heat. ...

At first sight this appears to offer a means of obtaining the standard molar enthalpy of the reaction by studying the variation of K with temperature. In practice, however, the method is unreliable because error propagation almost always gives very large errors on the values calculated in this way.

Types of equilibrium and some applications

1. In the gas phase. Rocket engines ^[13]
2. The industrial synthesis such as ammonia in the Haber-Bosch process (depicted right) takes place through a succession of equilibrium steps including adsorbtion processes.

1. atmospheric chemistry.
2. Seawater and other natural waters. Chemical oceanography.
3. Distribution between two phases.
   1. LogD-Distribution coefficient Important for pharmaceuticals where lipophilicity is a significant property of a drug.
   2. Liquid-liquid extraction, Ion exchange, Chromatography.
   3. Solubility product.
   4. Uptake and release of oxygen by haemoglobin in blood
4. Acid/base equilibria. Acid dissociation constant, hydrolysis, buffer solutions, indicators, acid-base homeostasis
5. Metal-ligand complexation. sequestering agents, chelation therapy, MRI contrast reagents, Schlenk equilibrium
6. Adduct formation. Host-guest chemistry, supramolecular chemistry, molecular recognition, dinitrogen tetroxide
7. In certain oscillating reactions the approach to equilibrium is not asymptotically but in the form of a damped oscillation ^[11].
8. The related Nernst equation in electrochemistry gives the difference in electrode potential as a function of redox concentrations.
9. When molecules on each side of the equilibrium are able to further react irreversibly in secondary reactions the final product ratio is determined according to the Curtin-Hammett principle.

In these applications terms such as stability constant, formation constant, binding constant, affinity constant, association/dissociation constant are used. In biochemistry it is common to give units for binding constants, which serve to define the concentration units used when the constant’s value was determined. A cold (un-ignited) rocket engine test at NASA A rocket engine is a reaction engine that can be used for spacecraft propulsion as well as terrestrial uses, such as missiles. ... For other uses, see Ammonia (disambiguation). ... The Haber Process (also Haber-Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... In chemistry, adsorption of a substance is its concentration on a particular surface. ... Image File history File links No higher resolution available. ... Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earths atmosphere and that of other planets is studied. ... Chemical oceanography is the study of the behaviour of the chemical elements within the Earths oceans. ... In the fields of organic and medicinal chemistry a partition or distribution coefficient (KD) is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium. ... Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their solution preferences for two different immiscible liquids, usually water and an organic solvent. ... Ion exchange is defined as an exchange of ions between two electrolytes. ... For the Second Person album, see Chromatography (album). ... It has been suggested that this article or section be merged with chemical equilibrium. ... 3-dimensional structure of hemoglobin Hemoglobin or haemoglobin is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. ... The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate... Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit Buffer solutions are solutions which resist change... In chemistry, indicators are chemical substances added to reaction mixtures when performing titrations. ... The body is very sensitive to its pH level. ... Chelation (from Greek χηλή, chelè, meaning claw; pronounced ) is the binding or complexation of a bi- or multidentate ligand. ... Chelation therapy is the administration of chelating agents to remove heavy metals from the body. ... “MRI” redirects here. ... The Schlenk equilibrium is a chemical equilibrium named after its discoverer Wilhelm Schlenk taking place in solutions of Grignard reagents. ... In supramolecular chemistry, host-guest chemistry describes complexes that are composed of two or more molecules or ions held together in unique structural relationships by hydrogen bonding or by ion pairing or by Van der Waals force other than those of full covalent bonds. ... Supramolecular chemistry refers to the area of chemistry which focuses on the noncovalent bonding interactions of molecules. ... Crystal structure of a short peptide L-Lys-D-Ala-D-Ala (bacterial cell wall precursor) bound to the antibiotic vancomycin through hydrogen bonds reported by Knox and Pratt in Antimicrob. ... Nitrogen tetroxide (or dinitrogen tetroxide) is the chemical compound N2O4. ... A Belousov-Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of non-equilibrium thermodynamics, resulting in the establishment of a nonlinear chemical oscillator. ... In electrochemistry, the Nernst equation gives the electrode potential (E), relative to the standard electrode potential, (E0), of the electrode couple or, equivalently, of the half cells of a battery. ... In chemical kinetics, the Curtin-Hammett principle states that, for a reaction that has a pair of reactive intermediates or reactants that interconvert rapidly (as is usually the case for conformers), each going to a different product, the product ratio will depend only on the difference in the free energy...

Composition of an equilibrium mixture

When the only equilibrium is that of the formation of a 1:1 adduct as the composition of a mixture, there are any number of ways that the composition of a mixture can be calculated. For example, see ICE table for a traditional method of calculating the pH of a solution of a weak acid. An ICE table or ICE chart is a tabular system of keeping track of changing concentrations in an equilibrium reaction. ...

There are three approaches to the general calculation of the composition of a mixture at equilibrium.

1. The most basic approach is to manipulate the various equilibrium constants until the desired concentrations are expressed in terms of measured equilibrium constants (equivalent to measuring chemical potentials) and initial conditions.
2. Minimize the Gibbs energy of the system. ^[14]
3. Satisfy the equation of mass balance. The equations of mass balance are simply statements that the total concentration of each reactant must be constant by the law of conservation of mass.

A mass balance (also called a material balance) is an accounting of material entering and leaving a system. ... The law of conservation of mass/matter, also known as law of mass/matter conservation (or the Lomonosov-Lavoisier law), states that the mass of a closed system of substances will remain constant, regardless of the processes acting inside the system. ...

Solving the equations of mass-balance

In general the calculations are rather complicated. For instance, in the case of a dibasic acid, H₂A dissolved in water the two reactants can be specified as the conjugate base, A^2-, and the proton, H⁺. The following equations of mass-balance could apply equally well to a base such as 1,2-diaminoethane, in which case the base itself is designated as the reactant A: In the field of chemistry, in the Brønsted-Lowry (protonic) theory of acids and bases, a conjugate base is the basic member, X-, of a pair of compounds that differ only by the presence or absence of a proton at a certain position. ... In chemistry, hydronium is the common name for the cation H3O+ derived from protonation of water. ... Ethylene diamine (EDA), or 1,2-diaminoethane, is an organic compound from the amines group. ...

With T_A the total concentration of species A. Note that it is customary to omit the ionic charges when writing and using these equations.

When the equilibrium constants are known and the total concentrations are specified there are two equations in two unknown "free concentrations" [A] and [H]. This follows from the fact that [HA]= β₁[A][H], [H₂A]= β₂[A][H]² and [OH] = K_w[H]^-1

so the concentrations of the "complexes" are calculated from the free concentrations and the equilibrium constants. General expressions applicable to all systems with two reagents, A and B would be

It is easy to see how this can be extended to three or more reagents.

Composition for polybasic acids as a function of pH

The composition of solutions containing reactants A and H is easy to calculate as a function of p[H]. When [H] is known the free concentration [A] is calculated from the mass-balance equation in A. Here is an example of the results that can be obtained. For other uses, see PH (disambiguation). ...

Image File history File links No higher resolution available. ...

This diagram, for the hydrolysis of the aluminum Lewis acid Al³⁺_aq ^[15] shows the species concentrations for a 5×10^-6M solution of an aluminium salt as a function of pH. Each concentration is shown as a percentage of the total aluminium. tra la la Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... In chemistry, a Lewis acid can accept a pair of electrons and form a coordinate covalent bond, after the American chemist Gilbert Lewis. ...

Solution equilibria with precipitation

The diagram above illustrates the point that a precipitate may be formed which is not one of the main species in the solution equilibrium. At pH just below 5.5 the main species present in a 5μM solution of Al³⁺ are aluminum hydroxides Al(OH)²⁺, Al(OH)₂⁺ and Al₁₃(OH)₃₂⁷⁺, but on raising the pH Al(OH)₃ precipitates from the solution. This occurs because Al(OH)₃ has a very large lattice energy. As the pH rises more and more Al(OH)₃ comes out of solution. This is an example of Le Chatelier's principle in action: increasing the concentration of the hydroxide ion causes more aluminium hydroxide to precipitate, which removes hydroxide from the solution. When the hydroxide concentration becomes sufficiently high the soluble aluminate, Al(OH)₄^-, is formed. ... Aluminium hydroxide, Al(OH)3, is the most stable form of aluminium in normal conditions. ... Diamond Crystal Lattice The lattice energy of an ionic solid is a measure of the strength of bonds in that ionic compound. ... In chemistry, Le Chateliers principle, also called the Le Chatelier-Braun principle, can be used to predict the effect of a change in conditions on a chemical equilibrium. ...

Another common instance where precipitation occurs is when a metal cation interacts with an anionic ligand to form an electrically neutral complex. If the complex is hydrophopbic it will precipitate out of water. This occurs with the nickel ion Ni²⁺ and dimethylglyoxime, (dmgH₂): in this case the lattice energy of the solid is not particularly large, but it greatly exceeds the energy of solvation of the molecule Ni(dmgH)₂. Dew drop on a hydrophobic leaf surface Water drops on the hydrophobic surface of grass For other uses, see Hydrophobia Hydrophobe or hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) in chemistry refers to the physical property of a molecule that is repelled... For other uses, see Nickel (disambiguation). ... This page is a candidate to be copied to Wiktionary. ... Solvation is the attraction and association of molecules of a solvent with molecules or ions of a solute. ...

Minimization of Gibbs energy

At equilibrium, G is at a minimum:

For a closed system, no particles may enter or leave, although they may combine in various ways. The total number of atoms of each element will remain constant. This means that the minimization above must be subjected to the constraints:

where a_ij is the number of atoms of element i in molecule j and b_i⁰ is the total number of atoms of element i, which is a constant, since the system is closed. If there are a total of k types of atoms in the system, then there will be k such equations.

This is a standard problem in optimisation, known as constrained minimisation. The most common method of solving it is using the method of Lagrange multipliers, also known as undetermined multipliers (though other methods may be used). In mathematics, the term optimization, or mathematical programming, refers to the study of problems in which one seeks to minimize or maximize a real function by systematically choosing the values of real or integer variables from within an allowed set. ... Fig. ...

Define:

where the λ_i are the Lagrange multipliers, one for each element. This allows each of the N_j to be treated independently, and it can be shown using the tools of multivariate calculus that the equilibrium condition is given by Multivariate calculus is a means of analyzing deterministic systems with multiple degrees of freedom. ...

    and    

(For proof see Lagrange multipliers) Fig. ...

This is a set of (m+k) equations in (m+k) unknowns (the N_j and the λ_i) and may therefore be solved for the equilibrium concentrations N_j as long as the chemical potentials are known as functions of the concentrations at the given temperature and pressure. (See Thermodynamic databases for pure substances). Thermodynamic databases contain information about thermodynamic properties for substances, the most important being enthalpy, entropy, and Gibbs free energy. ...

This method of calculating equilibrium chemical concentrations is useful for systems with a large number of different molecules. The use of k atomic element conservation equations for the mass constraint is straightforward, and replaces the use of the stoichiometric coefficient equations. ^[13]

See also

• Equilibrium constant
• Determination of equilibrium constants
• Henderson-Hasselbalch equation
• Michaelis-Menten kinetics
• Redox equilibria
• Thermodynamic databases for pure substances

In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction. ... Equilibrium constants are determined in order to quantify chemical equilibria. ... The Henderson-Hasselbalch (frequently misspelled Henderson-Hasselbach) equation in chemistry describes the derivation of pH as a measure of acidity (using pKa, the acid dissociation constant) in biological and chemical systems. ... Michaelis-Menten kinetics describes the kinetics of many enzymes. ... It has been suggested that Electrode potential be merged into this article or section. ... Thermodynamic databases contain information about thermodynamic properties for substances, the most important being enthalpy, entropy, and Gibbs free energy. ...

References

1. ^ Atkins & Jones, 2001
2. ^ Gold Book definition Link
3. ^ Chemistry: Matter and Its Changes James E. Brady , Fred Senese 4th Ed. ISBN 0471215171
4. ^ Chemical Principles: The Quest for Insight Peter Atkins, Loretta Jones 2nd Ed. ISBN 0716757010
5. ^ Physical Chemistry by Atkins, De Paula
6. ^ P.W. Atkins, Physical Chemistry, Oxford University Press, date
7. ^ a) Mary Jane Schultz. Why Equilibrium? Understanding the Role of Entropy of Mixing. Journal of Chemical Education 1999, 76, 1391. b) Clugston, Michael J. A mathematical verification of the second law of thermodynamics from the entropy of mixing. Journal of Chemical Education 1990, 67, 203.
8. ^ C.W. Davies, Ion Association,Butterworths, 1962
9. ^ ^{a b} I. Grenthe and H. Wanner, Guidelines for the extrapolation to zero ionic strength, http://www.nea.fr/html/dbtdb/guidelines/tdb2.pdf
10. ^ F.J,C. Rossotti and H. Rossotti, The Determination of Stability Constants, McGraw-Hill, 1961
11. ^ ^{a b c} Concise Encyclopedia Chemistry 1994 ISBN 0899254578
12. ^ M.T. Beck, Chemistry of Complex Equilibria, Van Nostrand, 1970. 2nd. Edition by M.T. Beck and I Nagypál, Akadémiai Kaidó, Budapest, 1990.
13. ^ ^{a b} NASA Reference publication 1311, Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications
14. ^ This approach is described in detail in W. R. Smith and R. W. Missen, Chemical Reaction Equilibrium Analysis: Theory and Algorithms, , Krieger Publishing, Malabar, Fla, 1991 (a reprint, with corrections, of the same title by Wiley-Interscience, 1982). A comprehensive treatment of the theory of chemical reaction equilibria and its computation. Details at http://www.mathtrek.com/
15. ^ The diagram was created with the program HySS

The Gold Book or Compendium of Chemical Terminology (ISBN 0865426848) is a book published by IUPAC containing internationally accepted definitions for terms in chemistry. ...

Further reading

• F. Van Zeggeren and S.H. Storey, The Computation of Chemical Equilibria, Cambridge University Press, 1970. Mainly concerned with gas-phase equilibria.
• D. J. Leggett (editor), Computational Methods for the Determination of Formation Constants, Plenum Press, 1985.
• A.E. Martell and R.J. Motekaitis, The Determination and Use of Stability Constants, Wiley-VCH, 1992.
• P. Gans, Stability Constants: Determination and Uses, an interactive CD, Protonic Software (Leeds), 2004

External links

Computer programs for calculating species concentrations

There are n mass-balance equations in n unknown free concentrations. This constitutes a set of non-linear equations which must be solved by a method of successive approximations. The most commonly used method is the Newton-Raphson method and this has been the subject of numerous publications. Some general computer programs are listed here. In numerical analysis, Newtons method (or the Newton-Raphson method) is an efficient algorithm for finding approximations to the zeros (or roots) of a real-valued function. ...

• HySS Titration simulation and speciation calculations.
• EQS4WIN A powerful computer program originally developed for gas-phase equilibria but subsequently extended to general applications. Uses the Gibbs energy minimization approach.
• CHEMEQLA comprehensive computer program for the calculation of thermodynamic equilibrium concentrations of species in homogeneous and heterogeneous systems. Many geochemical applications.
• WinSGW A Windows version of the SOLGASWATER computer program.
• Visual MINTEQ A Windows version of MINTEQA2 (ver 4.0). MINTEQA2 is a chemical equilibrium model for the calculation of metal speciation, solubility equilibria etc. for natural waters.
• MINEQL+ A chemical equilibrium modeling system for aqueous systems. Handles a wide range of pH, redox, solubility and sorption scenarios.

Software for chemical equilibria

• Aqua solution software A set of five computer programs for
• Specific Interaction Theory. An editable database of published SIT parameters. Estimation of SIT parameters and adjustment of stability constants for changes in ionic strength.
• Calculation of electrolyte activity coefficients, ionic activity coefficients, osmotic coefficients
• Calculation of acid-base equilibria in electrolyte solutions and sea water
• Calculation of O₂ solubility in water, electrolyte solutions, natural fluids and seawater as a function of temperature, concentration, salinity, altitude, external pressure, humidity
• Prediction of temperature dependence of lg K values using various thermodynamic models
• JESS:A powerful research tool for thermodynamic and kinetic modelling of chemical speciation in complex aqueous environments.
• Chemical Equilibrium Calculator