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In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction. It is a useful tool in determining the concentration of various reactants and products in a system where chemical equilibrium occurs. Chemistry - the study of atoms, made of nuclei (center particles) and electrons (outer particles), and the structures they form. ...
Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ...
A chemical reaction occurs when vapours of hydrogen chloride in a beaker and ammonia in a test tube meet to form a cloud of a new substance, ammonium chloride A chemical reaction is a process that results in the interconversion of chemical substances. ...
In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. ...
Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ...
Definition
A typical equilibrium situation is as below: where A and B are reactant chemical species, C and D are product species, and a, b, c, and d are the stoichiometric coefficients of the respective reactants and products. [[Media:[[Media: == 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 mathematics, a coefficient is a multiplicative factor that belongs to a certain object such as a variable (for example, the coefficients of a polynomial), a basis vector, a basis function and so on. ...
Equilibrium occurs when the forward reaction rate equals the backward reaction rate. Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ...
The equilibrium constant is defined as
![K stackrel{mathrm{def}}{=} frac{left[Cright]^c left[Dright]^d} {left[Aright]^a left[Bright]^b}](http://upload.wikimedia.org/math/f/1/1/f111fdf4c13e1c63c53ae4c96144b40d.png) The law of chemical equilibrium says that this constant is independent of initial concentrations or most reaction conditions except temperature. [J] represents the chemical activity of the species J at equilibrium under reaction conditions. Sometimes the activity can be replaced by molar concentration or partial pressure without significant error, yielding Kc or Kp respectively. K is dimensionless, while Kc and Kp are not necessarily so. Activity in chemistry is a measure of how different molecules in a non-ideal gas or solution interact with each other. ...
Derivations For single-step reactions, where the law of mass action is valid, we can write 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. ...
![k_{f} left[Aright]^a left[Bright]^b = k_{b} left[Cright]^c left[Dright]^d](http://upload.wikimedia.org/math/5/7/6/576ea0458d3458d4891e23721f38e6f5.png) where kf and kb are the forward and backward reaction rate constants, respectively. Cross-dividing yields In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction. ...
![K stackrel{mathrm{def}}{=} frac{k_{f}}{k_{b}} = frac{left[Cright]^c left[Dright]^d} {left[Aright]^a left[Bright]^b}](http://upload.wikimedia.org/math/6/1/f/61fa752541f021fb2f51cedb16c489ff.png) Since the rate constants are constant by definition, the law of chemical equilibrium is valid. But it should be kept in mind that this derivation is valid only for single-step elementary reactions (which are very rare) and not for general reactions where the law of mass action does not apply. Using this treatment for general reactions is an example of getting the right answer using the wrong method. The law of chemical equilibrium however holds for all reactions. The general derivation requires advanced treatment using thermodynamics. Thermodynamics (from the Greek thermos meaning heat and dynamics meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ...
Simple equilibrium
 Concentration of A (A 0 = 0.25 mole/l) and B versus time reaching equilibrium k f = 2 min -1 and k r = 1 min -1 In a simple equilibrium between two species: Image File history File links No higher resolution available. ...
Image File history File links No higher resolution available. ...
 the constant K at equilibrium is expressed as: ![K stackrel{mathrm{def}}{=} frac{k_{f}}{k_{b}} = frac{left[Bright]_e} {left[Aright]_e}](http://upload.wikimedia.org/math/0/5/b/05b33bde8d504ac56641d440c1e39e92.png) When the concentration of A at equilibrium is that of the concentration at time 0 minus the conversion in moles ![[A]_e = [A]_0 - x](http://upload.wikimedia.org/math/0/8/2/08214f2873c805d248b13e488c22856c.png) with x equal to the concentration of B at equilibrium ![[B]_e = x](http://upload.wikimedia.org/math/0/a/4/0a46fb91b7f8e3cea51c86be61592d0c.png) then it follows that ![[B]_e = x = frac{k_{-f}}{k_f+k_r}[A]_0](http://upload.wikimedia.org/math/a/7/9/a792bd235422058aef9d2c424f8929cf.png) and ![[A]_e = [A]_0 - x = frac{k_{-r}}{k_f+k_r}[A]_0](http://upload.wikimedia.org/math/7/2/b/72b0e19dee80f2f3ccfc7fbcb4214470.png) The reaction rate becomes: Iron rusting - a chemical reaction with a slow reaction rate. ...
![frac{dx}{dt} = frac{k_f[A]_0}{x_e} (x_e - x)](http://upload.wikimedia.org/math/8/6/0/86088ab72ea98fc027158d36f533563d.png) which results in: ![ln(frac{[A]_0 - [A]_e}{[A_t]-[A]_e}) = (k_f + k_r)t](http://upload.wikimedia.org/math/6/c/4/6c485a46a31086024e8c183cfabec06d.png) A plot of the negative natural logarithm of the concentration of A in time minus the concentration at equilibrium versus time t gives a straight line with slope kf + kr. By measurement of Ae and Be the values of K and the two reaction rate constants will be known. The natural logarithm, formerly known as the hyperbolic logarithm, is the logarithm to the base e, where e is equal to 2. ...
In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction. ...
When the equilibrium constant is close to unity and the reaction rates very fast for instance in conformational analysis of molecules, other methods are required for the determination of rate constants for instance by complete lineshape analysis in NMR spectroscopy. Conformational isomerism is the phenomenon of molecules with the same structural formula but different conformations (conformers) of atoms about a rotating bond. ...
There are very few or no other articles that link to this one. ...
It has been suggested that NMR Data Processing be merged into this article or section. ...
Applications Equilibrium constants can be defined for many physical/chemical processes. Examples include the acidity constant (the equilibrium constant for the dissociation of protons from acids) and the solubility constant (the equilibrium constant for precipitating out of solution). ...
It has been suggested that this article or section be merged with solubility. ...
Dissolving table salt in water This article is about a chemical solution; for other uses of the term solution, see solution (disambiguation). ...
There are certain implications of the equilibrium constant. If the value is very large, over 1, the reaction is said to lie to the right (of the arrow) indicating a greater concentration of products; values less than 1 lie to the left higher formation rates of reactants, and values of one indicate equal concentrations. Knowledge of the equilibrium constant helps to determine, in an industrial setting for example, how to best produce a desirable material.
For example, in the Haber process for the formation of ammonia, the value of K is around 30 at pressures and temperatures standard for the process. The Haber Process (also known as Haber–Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ...
Ammonia is a compound with the formula NH3. ...
The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ...
Fig. ...
In an equilibrium between two conformers with energy difference 0, the equilibrium constant is 1 and both conformers are present in a 1:1 ratio. When the energy difference increases to 1 kcal/mol, the equilibrium constant at 25 °C becomes around 5 and the concentration of the more stable conformer gets 85%. Conformational isomerism is the phenomenon of molecules with the same structural formula but different conformations (conformers) of atoms about a rotating bond. ...
A calorie is a unit of measurement for energy. ...
The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...
Thermodynamics It can be shown that the equilibrium constant is related to the standard Gibbs energy change of reaction as: Image File history File links Gibbs. ...
In thermodynamics, the Gibbs energy or Gibbs energy function is the energy portion of a thermodynamic system available to do work. ...
 , where ΔG° is the standard Gibbs energy change of reaction, R is the gas constant, and T the absolute temperature. The gas constant (also known as the universal or ideal gas constant, usually denoted by symbol R) is a physical constant used in equations of state to relate various groups of state functions to one another. ...
Absolute zero is the lowest temperature that can be obtained in any macroscopic system. ...
This relationship is also written as:
 A direct consequence of this important relation is the Van't Hoff equation, which relates the change in temperature to the change in the equilibrium constant given the enthalpy change. The related Nernst equation in electrochemistry gives the difference in electrode potential as a function of redox concentrations. The Vant Hoff equation in chemical thermodynamics relates the change in temperature to the change in the equilibrium constant given the enthalpy change. ...
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. ...
When molecules on each side of the equilibrium are able to further react in secondary reactions the final product ratio is determined according to the Curtin-Hammett principle. 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...
See also Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ...
In chemistry, Le Châteliers principle can be used to predict the effect of a change in conditions on a chemical equilibrium. ...
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). ...
Thermodynamic databases contain information about thermodynamic properties for substances, the most important being enthalpy, entropy, and Gibbs free energy. ...
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