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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
Chapter 4, Problem 20a

Draw a reaction coordinate diagram for a one step reaction that has the following values of Ea and ∆H. (a) Ea = 9 kcal/mol ; ∆H° = + 4 kcal/mol

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Step 1: Understand the reaction coordinate diagram. It is a graph that plots the energy of the system (y-axis) against the progress of the reaction (x-axis). Key features include the reactants, products, the transition state, and the activation energy (Eₐ).
Step 2: Identify the given values. The activation energy (Eₐ) is 9 kcal/mol, which represents the energy barrier between the reactants and the transition state. The enthalpy change (∆H°) is +4 kcal/mol, indicating that the reaction is endothermic (products are higher in energy than reactants).
Step 3: Begin sketching the diagram. Start by drawing a horizontal line to represent the energy level of the reactants. Then, draw a peak to represent the transition state, ensuring the height of the peak above the reactants corresponds to the activation energy (9 kcal/mol).
Step 4: Draw the energy level of the products. Since the reaction is endothermic (∆H° = +4 kcal/mol), the products should be at a higher energy level than the reactants. The difference in energy between the reactants and products should equal ∆H° (4 kcal/mol).
Step 5: Label the diagram. Clearly mark the reactants, products, transition state, activation energy (Eₐ), and enthalpy change (∆H°). Ensure the energy values are appropriately scaled and labeled on the y-axis for clarity.

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Key Concepts

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

Activation Energy (Eₐ)

Activation energy (Eₐ) is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to transform into products. In the context of a reaction coordinate diagram, Eₐ is depicted as the difference in energy between the reactants and the transition state, indicating how much energy must be supplied for the reaction to proceed.
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Enthalpy Change (∆H)

Enthalpy change (∆H) refers to the difference in energy between the products and the reactants in a chemical reaction. A positive ∆H indicates that the reaction is endothermic, meaning it absorbs heat from the surroundings. In a reaction coordinate diagram, ∆H is represented by the vertical distance between the reactants and products, providing insight into the energy dynamics of the reaction.
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Reaction Coordinate Diagram

A reaction coordinate diagram is a graphical representation that illustrates the energy changes during a chemical reaction as it progresses from reactants to products. The x-axis typically represents the reaction progress, while the y-axis shows the energy levels. Key features include the energy of the reactants, the transition state, and the products, allowing for visual analysis of activation energy and enthalpy changes.
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