Question

What are the dimensions of A in the expression \[k\text{ }=\text{ }A{{e}^{-\dfrac{Ea}{RT}}}\] ?

Answer 1

Hint: We know that the Arrhenius equation is used to calculate the rate of a reaction. It is an important part of chemical kinetics. It helps in understanding the effect of temperature on the rate of a reaction.

Complete answer:
As the unit of rate constants changes with change in order. For a second order reaction, the rate is directly proportional to the square of concentration of reactant. Rate of the reaction is defined as the change in concentration of reactant or product per unit time. As the reaction proceeds the concentration of the reactant decreases and the concentration of product increases. The rate of reaction is always positive. We generally study zero to third order reactions. For a zero-order reaction the unit of rate and rate constant is the same. Rate of a chemical reaction depends on the concentrations of reactants or products and the time required to complete the chemical change. Rate of a chemical reaction can be defined as the change in concentration of a reactant or product in unit time. The expression of the Arrhenius equation is:
\[k\text{ }=\text{ }A{{e}^{-\dfrac{Ea}{RT}}}\]
where,
k denotes the rate constant of the reaction,
A denotes the pre-exponential factor which, in terms of the collision theory, is the frequency of correctly oriented collisions between the reacting species,
e is the base of the natural logarithm;
Ea denotes the activation energy of the chemical reaction;
R denotes the universal gas constant;
T denotes the absolute temperature associated with the reaction (in Kelvin).
Thus, rate of a chemical reaction can be expressed on the basis of following points: The rate of decrease in concentration of any one of the reactants or the rate of increase in concentration of any one of the products Time taken in the change in concentration. The Arrhenius equation is important for the following reasons: it allows one to account for the factors which have an impact on the rate of a reaction which cannot be determined using the rate law.

Note:
Remember that the rate constant is a constant of proportionality. It depends upon the nature of reaction and temperature. At a constant temperature and at a particular reaction rate constant remains fixed. The basis of the Arrhenius equation is collision theory. According to this theory, a reaction is a collision between two molecules.