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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 54c
Chapter 4, Problem 54c

Draw a reaction coordinate diagram, making sure to label reactants (R), products (P), intermediates (I), transition states (‡), activation energies ( Ea) , and ∆G°, for each of the following.
(c) a slightly endothermic, three-step reaction where the first step is rate-determining

Verified step by step guidance
1
Start by understanding the reaction type: A slightly endothermic reaction means the overall free energy change (∆G°) is positive but small. A three-step reaction implies there are three distinct stages, each with its own transition state and possibly intermediates.
Draw the x-axis labeled as 'Reaction Coordinate' and the y-axis labeled as 'Energy'. This will represent the energy changes throughout the reaction.
Sketch the energy profile for the three steps. Begin with the reactants (R) at a lower energy level. The first step is rate-determining, so its transition state (‡) should have the highest energy barrier (Eₐ) compared to the other steps. Label the transition state for the first step as ‡₁.
Include intermediates (I) between each step. After the first transition state, draw an intermediate (I₁) at a lower energy level than ‡₁ but higher than the reactants. Repeat this process for the second and third steps, ensuring the intermediates (I₂, I₃) and transition states (‡₂, ‡₃) are appropriately placed.
Finally, label the products (P) at a slightly higher energy level than the reactants (R) to reflect the endothermic nature of the reaction. Indicate the overall ∆G° as the difference in energy between R and P. Ensure all activation energies (Eₐ) for each step are marked as the energy difference between the reactants/intermediates and their respective transition states.

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Key Concepts

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

Reaction Coordinate Diagram

A reaction coordinate diagram visually represents the energy changes during a chemical reaction. The x-axis typically shows the progress of the reaction, while the y-axis indicates the energy of the system. Key features include the energy levels of reactants, products, intermediates, and transition states, which help illustrate the energy barriers and overall energy change of the reaction.
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Endothermic Reaction

An endothermic reaction is one that absorbs energy from its surroundings, resulting in a positive change in enthalpy (∆H > 0). In such reactions, the energy of the products is higher than that of the reactants. This concept is crucial for understanding the energy profile of the reaction and how it affects the reaction coordinate diagram.
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Rate-Determining Step

The rate-determining step is the slowest step in a multi-step reaction mechanism, which dictates the overall reaction rate. It typically has the highest activation energy (Eₐ) and is represented by the highest peak in the reaction coordinate diagram. Understanding this concept is essential for accurately labeling the diagram and predicting the kinetics of the reaction.
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Related Practice
Textbook Question

Draw a reaction coordinate diagram, making sure to label reactants (R), products (P), intermediates (I), transition states (‡), activation energies ( Ea) , and ∆G°, for each of the following.

(a) an exothermic, one-step reaction

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Textbook Question

For each of the reaction coordinate diagrams shown, (i) indicate the number of steps in the reaction, (ii) label the intermediates, (iii) identify the rate-determining step, and (iv) tell whether Keq is greater than, less than, or equal to zero.

(a)

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Textbook Question

Calculate ∆H° for the following alkene addition reaction, one we discuss further in Chapter 7. Predict the sign of ∆S° . (The BDE for C―C π bond is approximately 65 kcal/mol.)

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Textbook Question

Draw a reaction coordinate diagram, making sure to label reactants (R), products (P), intermediates (I), transition states (‡), activation energies ( Ea) , and ∆G°, for each of the following.

(b) an exothermic, two-step reaction where the second step is rate-determining

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Textbook Question

Draw a reaction coordinate diagram, making sure to label reactants (R), products (P), intermediates (I), transition states (‡), activation energies ( Ea) , and ∆G°, for each of the following.

(d) a slightly exothermic, three-step reaction where the third step is rate-determining.

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Textbook Question

(b) Mechanistically, the reaction occurs as shown below. Why is this reaction favored? Based on the stability of the anions, estimate Keq.

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