For the zero-order reaction, the unit of rate coefficient is mol L- 1 S- 1? Or mol DM-3 s- 1.
For the first-order reaction, the unit of rate coefficient is s- 1.
For the second-order reaction, the unit of rate coefficient is L Mo- 1 S- 1? Or DM mol- 1 s- 1.
For the n-order reaction, the unit of rate coefficient is mol1-n ln-1s-1? Or mol 1-n dm3n-3? s- 1
In the rate equation of chemical reaction, the exponential algebraic sum of the concentration term of each substance is called the reaction series, which is expressed by n. The reaction rate equation can be expressed as: the reaction rate v is equal to the product of the rate constant k and the power of the coefficient of reactant concentration (regardless of the product).
Suppose the basic reaction is:
Its mathematical expression is:
In the above formula, the power of reactant concentration is the reaction order or series of reactants. For example, the order of reactant A is α, the order of reactant D is β, and the sum of reaction orders α+β is the reaction order of the reaction. The greater the reaction order, the greater the influence of concentration on the reaction rate.
Extended data
Generally speaking, the order of reactants in elementary reaction is consistent with its stoichiometric coefficient; Non-elementary reactions may be different, and their reaction order is determined by experiments, which may change with the change of experimental conditions. For example, the hydrolysis of sucrose is a second-order reaction, but when the amount of water in the reaction system is large, it can be considered that the amount of water in the system is unchanged before and after the reaction, then the reaction is realized as a first-order reaction.
In different series of rate equations, the unit of rate constant k is different, and it is generally ln-1.mol1-n.s-1,where n is the reaction order of the reaction.
The reaction order n of elementary reaction and simple reaction can be integer one, two or three (only a few reactions are three), while the reaction order n of complex reaction can also be fractional, negative and zero (photochemical reaction and surface catalytic reaction are generally zero). Negative sequence means that increasing the concentration of substances will reduce the reaction rate. However, if the reaction rate equation does not have a simple concentration product form, the concept of reaction series will lose its meaning. ?
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