What Is the Rate of Reaction?

Chemical reaction rate refers to how fast the chemical reaction proceeds. It is usually expressed by the change value (decrease value or increase value) of the concentration of reactants or products per unit time. The reaction speed is related to the nature and concentration of reactants, temperature, pressure, catalyst, etc. It is also related to the nature and amount of the solvent. Among them, the pressure relationship is small (except for gas reaction), and the influence of the catalyst is large. The reaction rate can be controlled by controlling the reaction conditions to achieve certain purposes. ^[1]

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1. In general, the chemical reaction rate changes with time, and the reaction rate is different at different times. Therefore, the instantaneous rate is usually used to indicate the reaction rate at t. The rate at which a chemical reaction begins is called the initial rate of the reaction.

2. The reaction rate of a chemical reaction is closely related to the reaction conditions. The same reaction is carried out under different conditions, and the reaction rate can be very different.

3. Concentration is another important factor affecting the reaction rate. Generally, the chemical reaction is reversible. When the positive reaction starts, the reverse reaction also follows, so the experimentally determined reaction rate is actually the difference between the positive reaction and the reverse reaction, that is, the net reaction rate. Of course, some reactions have inverse reaction rates. Of course, the reverse reaction rate of some reactions is very small and can be disregarded completely. It can be considered as a one-way reaction.

To measure the rate of a chemical reaction, it is necessary to determine the amount of change in the concentration of a substance in a unit time near a certain time. However, in general, the chemical reaction is still in progress during the measurement, and it is difficult to determine the reaction rate using general chemical analysis methods. An approximate method is to stop the reaction immediately (if possible). For example, by diluting, lowering the temperature, adding inhibitors, or removing the catalyst, the reaction can be made very slow and convenient for chemical analysis. However, this is time-consuming, labor-intensive, and inaccurate, and the response that can be studied is limited. Now widely used methods are to measure the properties of substances, such as pressure, conductivity, absorbance, etc., and realize continuous determination through their relationship with substance concentration. ^[4]