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Enthalpy–entropy Compensation
In thermodynamics, enthalpy–entropy compensation is a specific example of the compensation effect. The compensation effect refers to the behavior of a series of closely related chemical reactions (e.g., reactants in different solvents or reactants differing only in a single substituent), which exhibit a linear relationship between one of the following chemical kinetics, kinetic or thermodynamic parameters for describing the reactions: # Between the logarithm of the pre-exponential factors (or prefactors) and the Activation energy, activation energies \ln A_i = \alpha + \frac where the series of closely related reactions are indicated by the Indexed family, index , are the preexponential factors, are the activation energies, is the gas constant, and , are constants. # Between Activation enthalpy, enthalpies and Entropy of activation, entropies of activation (enthalpy–entropy compensation) \Delta H^\ddagger_i = \alpha + \beta \Delta S^\ddagger_i where are the enthalpies of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermodynamics
Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of thermodynamics, which convey a quantitative description using measurable macroscopic physical quantity, physical quantities but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to various topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering, and mechanical engineering, as well as other complex fields such as meteorology. Historically, thermodynamics developed out of a desire to increase the thermodynamic efficiency, efficiency of early steam engines, particularly through the work of French physicist Nicolas Léonard Sadi Carnot, Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arrhenius Plot
In chemical kinetics, an Arrhenius plot displays the logarithm of a reaction rate constant, ordinate axis) plotted against reciprocal of the temperature abscissa). Arrhenius plots are often used to analyze the effect of temperature on the rates of chemical reactions. For a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined. The Arrhenius equation can be given in the form: k = A \exp\left(\frac\right) = A \exp\left(\frac\right) where: * k = rate constant * A = pre-exponential factor * E_\text = (molar) activation energy * R = gas constant, (R=k_\text N_\text, where N_\text is the Avogadro constant). * E_\text' = activation energy (for a single reaction event) * k_\text = Boltzmann constant * T = absolute temperature The only difference between the two forms of the expression is the quantity used for the activation energy: the former would have the unit j ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Copper Chromite
Copper chromite often refers to inorganic compounds with the formula . They are black solids. is a well-defined material. The other copper chromite often is described as . It is used to catalyze reactions in organic chemistry. History Copper chromite was first described in 1908. The catalyst was further developed by Homer Burton Adkins and Wilbur Arthur Lazier, partly based on interrogation of German chemists after World War II in relation to the Fischer–Tropsch process. For this reason it is sometimes referred to as the Adkins catalyst or the Lazier catalyst. Adkins was the first to incorporate barium into the structure, which prevents the catalyst from being reduced to an inactive form during hydrogenation reactions. Chemical structures The stoichiometry of the Laziar or Adkins catalyst is not well defined, thus the structure of their material is not defined either. The oxidation states for the constituent metals in Cu2Cr2O4 are Cu(II) and Cr(III). A variety of compo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primary Alcohols
A primary alcohol is an Alcohol (chemistry), alcohol in which the hydroxy group is bonded to a primary carbon atom. It can also be defined as a molecule containing a “–CH2OH” group. In contrast, a secondary alcohol has a formula “–CHROH” and a tertiary alcohol has a formula “–CR2OH”, where “R” indicates a carbon-containing group. Examples of primary alcohols include ethanol, 1-propanol, and n-Butanol, 1-butanol. Methanol is also generally regarded as a primary alcohol, including by the 1911 edition of the Encyclopædia Britannica. See also * Alcohol (chemistry), Alcohol (especially Nomenclature section for discussion on Secondary and Tertiary alcohols.) * Oxidation of primary alcohols to carboxylic acids References Primary alcohols, {{organic-chem-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dehydrogenation
In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At its simplest, it is a useful way of converting alkanes, which are relatively inert and thus low-valued, to olefins, which are reactive and thus more valuable. Alkenes are precursors to aldehydes (), alcohols (), polymers, and aromatics. As a problematic reaction, the fouling and inactivation of many catalysts arises via coking, which is the dehydrogenative polymerization of organic substrates. Enzymes that catalyze dehydrogenation are called dehydrogenases. In metal manufacturing and repairs, dehydrogenation is a thermal treatment which consists in removing the hydrogen absorbed by an object during an electrochemical or chemical process, performed in a specific oven at a temperature of for a minimum time of 2 hours. Heterogeneous cat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reaction Quotient
In chemical thermodynamics, the reaction quotient (''Q''r or just ''Q'') is a dimensionless quantity that provides a measurement of the relative amounts of products and reactants present in a reaction mixture for a reaction with well-defined overall stoichiometry at a particular point in time. Mathematically, it is defined as the ratio of the activity (chemistry), activities (or Molar mass, molar concentrations) of the product species over those of the reactant species involved in the chemical reaction, taking stoichiometric coefficients of the reaction into account as exponents of the concentrations. In equilibrium, the reaction quotient is constant over time and is equal to the equilibrium constant. A general chemical reaction in which ''α'' mole (chemistry), moles of a reactant A and ''β'' moles of a reactant B react to give ''ρ'' moles of a product R and ''σ'' moles of a product S can be written as :\it \alpha\,\rm A + \it \beta\,\rm B \it \rho\,\rm R + \it \sigma\,\rm S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brønsted Catalysis Equation
The Brønsted catalysis equation or law of correlation, after Johannes Nicolaus Brønsted, gives the relationship between acid strength and catalytic activity in general acid catalysis. :\log k = \alpha*\log(K_a) + C A plot of the common logarithm of the reaction rate constant k versus the logarithm of the ionization constant Ka for a series of acids (for example a group of substituted phenols or carboxylic acids) gives a straight line with slope α and intercept C. The Brønsted equation is a free-energy relationship. The relationship implies that the Gibbs free energy for proton dissociation is proportional to the activation energy for the catalytic step. When the relationship is not linear, the chosen group of catalysts do not operate through the same reaction mechanism. Specific and general catalysis is also found in base catalysed reactions and base Brønsted equation also exists with constant β. The Brønsted equation gives information about a reaction mechanism. Reac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged Atomic nucleus, atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as Alcohol (chemistry), alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. The difference between the two is, that basicity is a thermodynamic property (i.e. relates to an equilibrium state), but nucleop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hammett Equation
In organic chemistry, the Hammett equation describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents to each other with just two parameters: a substituent constant and a reaction constant. This equation was developed and published by Louis Plack Hammett in 1937 as a follow-up to qualitative observations in his 1935 publication. The basic idea is that for any two reactions with two aromatic reactants only differing in the type of substituent, the change in free energy of activation is proportional to the change in Gibbs free energy. This notion does not follow from elemental thermochemistry or chemical kinetics and was introduced by Hammett intuitively. The basic equation is: :\log \frac = \sigma\rho where :_0 = Reference constant :\sigma = Substituent constant :\rho = Reaction rate constant relating the equilibrium constant, , for a given equilibrium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linear Free-energy Relationship
In physical organic chemistry, a free-energy relationship or Gibbs energy relation relates the logarithm of a reaction rate constant or equilibrium constant for one series of chemical reactions with the logarithm of the rate or equilibrium constant for a related series of reactions. Free energy relationships establish the extent at which Chemical bond, bond formation and Bond cleavage, breakage happen in the Transition state theory, transition state of a reaction, and in combination with Kinetic isotope effect, kinetic isotope experiments a reaction mechanism can be determined. Free energy relationships are often used to calculate equilibrium constants since they are experimentally difficult to determine. The most common form of free-energy relationships are linear free-energy relationships (LFER). The Brønsted catalysis equation describes the relationship between the ionization constant of a series of catalysts and the reaction rate constant for a reaction on which the catalyst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Van 't Hoff Plot
The Van 't Hoff equation relates the change in the equilibrium constant, , of a chemical reaction to the change in temperature, ''T'', given the standard enthalpy change, , for the process. The subscript r means "reaction" and the superscript \ominus means "standard". It was proposed by Dutch chemist Jacobus Henricus van 't Hoff in 1884 in his book ''Études de Dynamique chimique'' (''Studies in Dynamic Chemistry''). The Van 't Hoff equation has been widely utilized to explore the changes in state functions in a thermodynamic system. The Van 't Hoff plot, which is derived from this equation, is especially effective in estimating the change in enthalpy and entropy of a chemical reaction. Equation Summary and uses The standard pressure, P^0, is used to define the reference state for the Van 't Hoff equation, which is where denotes the natural logarithm, K_ is the thermodynamic equilibrium constant, and is the ideal gas constant. This equation is exact at any one t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
