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Exception(Arrhenius Theory), Effective Activation Energy is considered one of the most asked concept.
130 Questions around this concept.
Two reactions R1 and R2 have identical pre-exponential factors. The activation energy of R1 exceeds that of R2 by 10 kJ mol−1. If k1 and k2 are rate constants for reactions R1 and R2 respectively at 300 K, then ln(k2/k1) is equal to :
(R=8.314 J mol−1K−1)
How does an increase in temperature affect the rate of a reaction, according to transition state theory?
In collision theory of chemical reaction, represents
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Rate of a reaction can be expressed by Arrhenius equation as : . In this equation, represents
The rate of the reaction is given by the rate equation rate=k [NO]2 [Cl2]
The value of the rate constant can be increased by:
Consider the reaction having rate constant (k). If , then
Activation energy (Ea) and rate constants (k1 and k2) of a chemical reaction at two different temperatures (T1 and T2 ) related by :
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For a gaseous reaction, the rate constant (k) is . If the rate constant increases by a factor of 3 as the temperature is raised to What is the activation energy (Ea) for the reaction?
Two recreations and have identical pro -exponential factors. Activation energy of rate constants for reactions and respectively at , the in equal to.
In the respect of the equation in chemical kinetics, which one of the following statements is correct?
We know that on increasing the temperature, the rate of the reaction or rate constant increases.
The rate equation is given as follows:
Here k is the rate constant
Now, we will see the relation between k and T or also known as 'approximate dependency of k on T'.
Generally on 10oC rise in temperature, rate constant nearly doubles.
Temperature Coefficient: It is the ratio of two rate constants. Thus, mathematically it is given as:
Thus, the temperature coefficient is showing the dependency of the rate constant(k) on temperature(T).
NOTE: The standard value of the temperature coefficient is given at t = 25oC and (t+10) = 35oC.
The temperature dependence of the rate of a chemical reaction can be accurately explained by Arrhenius equation. It was first proposed by Dutch chemist, J.H. van’t Hoff but Swedish chemist, Arrhenius provided its physical justification and interpretation.
where A is the Arrhenius factor or the frequency factor. It is also called pre-exponential factor. It is a constant specific to a particular reaction. R is gas constant and Ea is activation energy measured in joules/mole(J mol–1).
We have the rate constant K1 at temperature T1 and rate constant K2 at temperature T2.
We know that the Arrhenius equation is given as follows:
On subtracting equation (i) from (ii), we get:
Although the Arrhenius equation explains the exact relationship between the rate of reaction and the temperature but there are still some exceptions in this theory. Actually, on increasing the temperature rate may decrease sometimes and may not follow Arrhenius equation. Following examples will illustrate these exceptions.
On the basis of mechanism, we have two types of reactions:
Simple or Elementary reaction
Complex Reaction
Important Facts:
This example will illustrate how to determine the rate law when the intermediate is involved in rate-determining step.
Mechanism
In this case, step 1 is fast and step 2 is slow.
The rate law is given as follows:
We know from equilibrium theory that:
In this situation, B and C both are forming. These types of reactions are known as parallel reactions. Both these reactions are first order reactions with rate constants K1 and K2 respectively and half-lives as t(1/2)1 and t(1/2)2.
For these parallel reactions, we need to find:
We know that the rate equations are given as follows:
NOTE: Effective activation energy, [A], [B], [C] with time (t) variation and % of [B] and % of [C] will be discussed in later concepts.
We know that Arrhenius equation is given as:
We know that the rate equations are given as follows:
The overall rate of the reaction is:
On integrating both sides of the above equation, we get:
Now, the rate equation for B can be given as follows:
Similarly, [C] is given as follows:
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