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Reaction rate

The reaction rate or rate of reaction is the speed at which reactants are converted into products. For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second. For most reactions, the rate decreases as the reaction proceeds. The reaction rate or rate of reaction is the speed at which reactants are converted into products. For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second. For most reactions, the rate decreases as the reaction proceeds. Chemical kinetics is the part of physical chemistry that studies reaction rates. The concepts of chemical kinetics are applied in many disciplines, such as chemical engineering, enzymology and environmental engineering. Consider a typical chemical reaction: The lowercase letters (a, b, p, and q) represent stoichiometric coefficients, while the capital letters represent the reactants (A and B) and the products (P and Q). According to IUPAC's Gold Book definitionthe reaction rate r for a chemical reaction occurring in a closed system under isochoric conditions, without a build-up of reaction intermediates, is defined as: where denotes the concentration of the substance X (= A, B, P or Q). Reaction rate thus defined has the units of mol/L/s. The rate of a reaction is always positive. A negative sign is present to indicate that the reactant concentration is decreasing.) The IUPAC recommends that the unit of time should always be the second. The rate of reaction differs from the rate of increase of concentration of a product P by a constant factor (the reciprocal of its stoichiometric number) and for a reactant A by minus the reciprocal of the stoichiometric number. The stoichiometric numbers are included so that the defined rate is independent of which reactant or product species is chosen for measurement.:349 For example, if a = 1 and b = 3 then B is consumed three times more rapidly than A, but v = -d/dt = -(1/3)d/dt is uniquely defined. An additional advantage of this definition is that for an elementary and irreversible reaction, r is equal to the product of probability of overcoming the transition state activation energy and the number of times per second the transition state is approached by reactant molecules. When so defined, for an elementary and irreversible reaction, r is the rate of successful chemical reaction events leading to the product. The above definition is only valid for a single reaction, in a closed system of constant volume, an assumption which should be stated explicitly in the definition. If water is added to a pot containing salty water, the concentration of salt decreases, although there is no chemical reaction. For an open system, the full mass balance must be taken into account: in − out + generation − consumption = accumulation

[ "Kinetics", "Catalysis", "Bromamine B", "Chloramine B", "Tetranitro-BT", "maximum reaction rate", "N-bromophthalimide" ]
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