Question Details

Activation energy of any chemical reaction can be calculated if one knows the value of

Options

A

rate constant at standard temperature

B

probability of collision

C

orientation of reactant molecules during collision

D

rate constant at two different temperatures

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Correct Answer :

Option D

rate constant at two different temperatures

rate constant at two different temperatures

Solution :

The correct answer is rate constant at two different temperatures.

To understand why, we can refer to the Arrhenius equation, which describes the quantitative relationship between the rate constant of a chemical reaction and the absolute temperature:
k=Ae-Ea/RT
where:
k is the rate constant of the reaction,
A is the pre-exponential factor (or frequency factor),
Ea is the activation energy,
R is the universal gas constant, and
T is the absolute temperature (in Kelvin).

Taking the natural logarithm of both sides of the Arrhenius equation:
lnk=lnA-EaRT
If we determine the rate constant at two different temperatures, say T1 and T2, the corresponding rate constants are k1 and k2 respectively. Writing the logarithmic form for both conditions:
lnk1=lnA-EaRT1
and
lnk2=lnA-EaRT2
By subtracting the equation for k1 from the equation for k2, we eliminate the unknown pre-exponential factor A:
lnk2-lnk1=lnA-EaRT2-lnA-EaRT1
Simplifying the relationship:
lnk2k1=EaR1T1-1T2
Converting the natural logarithm (ln) to base-10 logarithm (log):
logk2k1=Ea2.303RT2-T1T1T2

From this final integrated expression, we can conclude that the activation energy (Ea) can be calculated if we know the rate constant at two different temperatures.

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