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Physical Chemistry

The correct statement about the pre-exponential factor in Arrhenius equation is that

Question

The correct statement about the pre-exponential factor in Arrhenius equation is that

it is dimensionless.

it necessarily has s^-1 in its dimension, regardless of the order of the reaction.

it does not necessarily have s^-1 in its dimension.

it has concentration in its dimension, regardless of the order of the reaction.

Solution

Correct option is B

Arrhenius proposed the following empirical equation for calculating the energy of activation of a reaction having rate constant k at temperature T:

where Ea is called the Arrhenius activation energy and A is called the Arrhenius pre-exponential factor. Since the exponential factor is dimensionless, the pre-exponential factor A has the same units as the rate constant k. The units of k for a first-order reaction are s^-1, which is the unit of frequency. Hence, A is also called the frequency factor. Ea, and A are called the Arrhenius parameters.