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What is a frequency factor or pre-expone...

What is a frequency factor or pre-exponential factor?

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In Arrhenius equation, `k=Axx e^(-Ea//RT)` the factor A is called frequency factor and since it is a coefficient of exponential expression, `e^(-E_(a)//RT)` it is also called pre-exponential factor.
In the above equation k is a rate constant at temperature T, `E_(a)` is the energy of activation and R is a gas constant.
A is related to frequency of collisions (Z) or rate of collisions. It is represented as, `A=PxxZ` where P is the probability of collisions with proper orientations and Z is the frequency of collisions of reacting molecules .
The units of A are same as that of k.
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Knowledge Check

  • The rate of a reaction ((dx)/(dt)) varies with nature, physical state and concentration of reactants, temperature, exposure to light and catalyst, whereas rate constant (K) varies with temperature and catalyst only. The rate constant K is given as K=Ae^(pmE_(a)//RT) where A is Arrhenius parameter or pre-exponential factor and E_(a) is energy of activation. The minimum energy required for a reaction is called threshold energy and the additional energy required by reactant molecules to attain threshold energy level is called energy of activation. At what conditions exponential factor is 1 for a reaction:

    A
    Infinite temperature
    B
    Free radical combination
    C
    `E_(a) =0`
    D
    All of these

  • The rate of reaction ((dx)/(dt)) varies with nature, physical state and concentration of reactants, temperature, exposure to light and catalyst, whereas rate constant (K) varies with temperature and catalyst only. The rate constant K is given as K=Ae^(-E_(a)//RT) where A is Arrhenius parameter or pre-exponential factor and E_(a) is energy of activation. The minimum energy required for a reaction is called threshold energy and the additional energy required by reactant molecules to attain threshold energy level is called energy of activation. At what conditions exponential factor is zero a reaction?

    A
    (a) Inifinite remperature
    B
    (b) Free radical combination
    C
    (c ) Energy of activation = Threshold energy
    D
    (d) All of these

  • The rate constant of a reaction will be equal to the pre-exponential factor when

    A
    Temperature in centigrade is zero.
    B
    The absolute temperature is zero.
    C
    The absolute temperature is infinity.
    D
    No suitable answer.

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