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Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 5 - Chemical Reaction Analysis: Thermodynamics and KineticsProblem 26a
Chapter 4, Problem 26a

Within the following pairs, pick which reaction you would expect to be faster based on having a higher value of the frequency factor (A).
(a) Chemical reaction energy diagrams comparing two reactions with different frequency factors, highlighting reaction pathways and intermediates.

Verified step by step guidance
1
Understand the concept of the frequency factor (A): The frequency factor is a component of the Arrhenius equation, which describes the rate constant (k) of a reaction. The equation is: k = A e-ERT. Here, A represents the frequency of collisions with the correct orientation for a reaction to occur.
Analyze the factors affecting the frequency factor (A): A depends on the molecular structure, size, and complexity of the reactants. Simpler molecules with fewer steric hindrances and more favorable orientations for collisions typically have higher values of A.
Compare the molecular structures of the reactants in the given pairs: Examine the size, complexity, and steric hindrance of the molecules in each pair. Simpler and less hindered molecules are expected to have a higher frequency factor.
Consider the reaction mechanism: If one reaction involves a simpler mechanism (e.g., fewer steps or less steric hindrance in the transition state), it is likely to have a higher frequency factor.
Select the faster reaction based on A: Based on the analysis of molecular structure and reaction mechanism, identify which reaction in the pair is expected to have a higher frequency factor and thus proceed faster.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Frequency Factor (A)

The frequency factor, often denoted as A in the Arrhenius equation, represents the frequency of collisions between reactant molecules that can lead to a reaction. A higher frequency factor indicates that the reactants are more likely to collide in the correct orientation and with sufficient energy to overcome the activation energy barrier, thus increasing the reaction rate.
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Activation Energy (Ea)

Activation energy is the minimum energy required for a chemical reaction to occur. It is a crucial factor in determining the rate of a reaction; reactions with lower activation energies tend to proceed faster because a greater proportion of the reactant molecules have enough energy to overcome this barrier during collisions.
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Reaction Mechanism

A reaction mechanism is a step-by-step description of the pathway taken by reactants to form products. Understanding the mechanism helps in predicting which reactions will be faster, as it provides insight into the number of elementary steps involved and the energy changes associated with each step, influencing both the frequency factor and activation energy.
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Related Practice
Textbook Question

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(b)

1
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Textbook Question

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(a)

2
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Textbook Question

For the reaction coordinate diagram shown, is the forward or reverse reaction faster?

2
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Textbook Question

For the following acid–base reactions studied in Assessment 5.25, draw a likely transition state. Be sure to indicate in your drawing the degree to which bonds are broken or formed.

(a)

1
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Textbook Question

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(c)

2
views
Textbook Question

Within the following pairs, pick which reaction you would expect to be faster based on having a higher value of the frequency factor (A).

(b)

5
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