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This equation assists in establishing a relationship between the rate constant of a specific chemical reaction and the pre-exponential factor, A, as well as the absolute temperature. It also provides an understanding of how reaction rates are affected by the absolute temperature of the environment. The Arrhenius equation can be represented by the following formula:
𝑘=𝐴𝑒−𝐸𝑎𝑅𝑇
The rate constant of the reaction is denoted by the letter k.
This component is referred to as the pre-exponential factor, and it is defined as the frequency of properly oriented collisions between the species that are interacting.
The letter e stands for the base of the natural logarithm, which is also known as Euler’s number.
The activation energy of a chemical process is indicated by the symbol Ea (denoted by energy per mole).
The universal gas constant is denoted by the letter R.
In this case, T denotes the absolute temperature that is associated with the reaction (denoted in Kelvin).
If the activation energy is expressed as a function of the energy per reactant molecule, then the universal gas constant must be substituted with another constant in the Arrhenius equation, known as the Boltzmann constant, abbreviated as kB.
Arrhenius equation chemical kinetics will be discussed in this article, as will the Arrhenius equation derivation and the application of the Arrhenius equation to find the energy of activation.
Does Arrhenius Equation Account for the Catalysts?
A catalyst is a substance that aids in lowering the amount of activation energy required by a specific reaction. For the purpose of obtaining the rate constant of the catalyzed reaction, the lowered activation energy that is accounted for by the catalysts is substituted in an Arrhenius equation.
When the activation energy declines, the exponential section of the Arrhenius equation, indicated by (-Ea/RT), results in an exponential increase in the value of the rate constant. Because we know that the rate of a chemical reaction is exactly related to the rate constant of that particular reaction, when the activation energy of the reaction is reduced, the rate of the reaction increases exponentially.
The rate of uncatalyzed reactions is affected by temperature more severely than the rate of catalyzed reactions, something you should be aware of when comparing the rates of the two. Due to the fact that the activation energy is contained within the numerator of the exponential term, and the absolute temperature is contained within the denominator of the Arrhenius equation, this is the case. When compared to the uncatalyzed reaction, the activation energy of the catalyzed reaction is lower, which makes the effect of temperature on the rate constant much more obvious when compared to the catalyzed process.
Arrhenius Equation and Pre-Exponential Factor (A)
The pre-exponential component, also known as the frequency factor, is denoted by the letter A in the Arrhenius equation, which is represented by the symbol A. This factor is concerned with the collisions that occur between molecules, and it is conceived of as the frequency of correctly oriented collisions that occur between molecules that have sufficient energy to cause a chemical reaction to occur between the two molecules.
The pre-exponential factor can be represented by the following equation:A = ⍴Z.
Specifically, Z is referred to as the frequency factor, or the frequency of collisions, and ⍴ is referred to as the steric factor, which deals with the orientation of the molecules in the collision.
Due to the fact that it has a tendency to assume numerous different values for a variety of different reactions, the value of A must be determined experimentally. It is also dependent on the temperature at which the reaction takes place to be effective.
Implications
Arrhenius’ equation contains an exponential element, which suggests that when an activation energy is reduced, the rate constant of a reaction increases exponentially, as seen in Figure 1. In addition, the rate of a reaction increases exponentially because the rate constant of a reaction is exactly proportional to the rate of the reaction. Because a reaction with a lower activation energy does not necessitate the expenditure of significant energy to reach the transition state, it should occur more quickly than a reaction with a larger activation energy.
Furthermore, according to the Arrhenius equation, the rate of an uncatalyzed reaction is more sensitive to temperature than the rate of a catalyzed reaction is to temperature. This is due to the fact that the activation energy of an uncatalyzed reaction is greater than the activation energy of the corresponding catalyzed reaction in the same process. Because the activation energy is included in the numerator of the exponential term and the temperature is included in the denominator, a lesser activation energy will have a smaller impact on the rate constant when compared to a greater activation energy. The pace of an uncatalyzed reaction is therefore more sensitive to temperature variations than the rate of a catalyzed reaction is.
COLLISION THEORY
It is possible to forecast chemical reaction rates using collision theory, which is especially useful when dealing with gasses. It is predicated on the concept that, in order for any particular reaction to take place, the reacting molecules or atoms must collide with one another or come together. Not all impacts, on the other hand, can result in a chemical change.
CONCLUSION
Collisions are effective in producing a chemical change only when the species that are brought together possess a specified value of minimum internal energy, which is equivalent to the activation energy of the reaction that is taking place. Furthermore, the species that are colliding should be orientated in a way that is conducive to the necessary rearrangement of the electrons and atoms that results from the collision. The collision hypothesis predicts that the pace at which any given chemical reaction tends to occur is the same as the frequency of effective collisions, as seen in the graph below.
