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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 72a
Chapter 4, Problem 72a

Parts (a)–(f) of this assessment refer to the rotation around the single bond of ethane.

(a) Given that the rate of the reaction is independent of concentration, fill in the missing rates in the following table.
Table showing trials with concentration of ethane and corresponding reaction rates, with some rates missing.

Verified step by step guidance
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Step 1: Understand the concept of rotation around a single bond in ethane. Ethane (C₂H₆) has a single bond between the two carbon atoms, and the rotation around this bond leads to different conformations (e.g., staggered and eclipsed). The energy barrier for this rotation is due to torsional strain.
Step 2: Recognize that the rate of reaction being independent of concentration indicates a zero-order reaction. In zero-order reactions, the rate is constant and does not depend on the concentration of reactants.
Step 3: Analyze the given table and identify the missing rates. Since the rate is constant in a zero-order reaction, all rates in the table should be the same regardless of the concentration values.
Step 4: Use the concept of zero-order kinetics to fill in the missing rates. The rate can be expressed mathematically as: Rate = k, where k is the rate constant.
Step 5: Ensure consistency in the table by verifying that all rates match the constant rate value provided or calculated based on the zero-order reaction principle.

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Key Concepts

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

Ethane Structure and Conformation

Ethane (C2H6) consists of two carbon atoms connected by a single bond, allowing for rotation around this bond. This rotation leads to different conformations, such as staggered and eclipsed forms, which influence the molecule's stability and energy. Understanding these conformations is essential for analyzing reaction rates and mechanisms involving ethane.
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Understanding what a conformer is.

Reaction Rate and Concentration Independence

In chemical kinetics, the reaction rate is often dependent on the concentration of reactants. However, if a reaction's rate is independent of concentration, it suggests that the reaction may be zero-order with respect to the reactants involved. This concept is crucial for filling in missing rates in the provided table, as it indicates that changes in concentration do not affect the rate of the reaction.
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Rates of Intramolecular Reactions Concept 2

Kinetic Theory and Activation Energy

Kinetic theory explains how the energy of molecules affects reaction rates. Activation energy is the minimum energy required for a reaction to occur. In the context of ethane's rotation, understanding how energy barriers influence the rate of conformational changes is vital, especially when considering that the reaction rate remains constant despite concentration changes.
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Introduction to free energy diagrams.
Related Practice
Textbook Question

The halogenation of an alkane when there is an alkene present in the molecule does not proceed with the regioselectivity you might expect. Using principles similar to those developed in this chapter, rationalize the formation of A as the only product. We study this reaction further in Chapter 8.

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Textbook Question

Parts (a)–(f) of this assessment refer to the rotation around the single bond of ethane.

(b) What is the order of the reaction with regard to ethane?

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Textbook Question

When a student attempted a bromination to produce compound A, they generated compound B instead. Rationalize the formation of B using the arrow-pushing formalism.

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Textbook Question

Parts (a)–(f) of this assessment refer to the rotation around the single bond of ethane.

(c) Write the rate law for this reaction.

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Textbook Question

In Chapter 13, we discuss the ring-opening reactions of epoxides, such as the one shown here.

(b) Predict the sign of ∆S°.

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Textbook Question

For rotation around a bond, the rate constant is equal to the reaction rate. Why?

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