Textbook Question
The temperature dependence of the rate constant for a reaction is tabulated as follows: Temperature (K) k 1M 1 s1 2 600 0.028 650 0.22 700 1.3 750 6.0 800 23 Calculate Ea and A.
Ch.14 - Chemical Kinetics
Chapter 14, Problem 66
(a) Can an intermediate appear as a reactant in the first step of a reaction mechanism? (b) On a reaction energy profile diagram, is an intermediate represented as a peak or a valley?
Verified step by step guidance1
Step 1: Understand what an intermediate is in a reaction mechanism. An intermediate is a species that is formed in one step of a reaction mechanism and consumed in a subsequent step. It is not present in the overall balanced equation for the reaction.
Step 2: Consider the role of an intermediate in a reaction mechanism. Since an intermediate is formed during the reaction process, it cannot appear as a reactant in the first step of the mechanism. It must be produced first before it can be consumed.
Step 3: Examine a reaction energy profile diagram. This diagram plots the potential energy of the system as the reaction progresses from reactants to products.
Step 4: Identify the features of a reaction energy profile diagram. Peaks on the diagram represent transition states, which are high-energy states that occur between reactants and intermediates or intermediates and products.
Step 5: Determine where intermediates appear on the energy profile. Intermediates are represented as valleys on the diagram, indicating a lower energy state between two transition states.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reaction Mechanism
A reaction mechanism is a step-by-step description of the pathway taken during a chemical reaction. It outlines the sequence of elementary steps, including the formation and consumption of intermediates. Understanding the mechanism helps in predicting the rate and outcome of the reaction, as well as the role of each species involved.
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Reaction Mechanism Overview
Intermediates
Intermediates are species that are formed during the course of a reaction but are not present in the final products. They are typically unstable and exist only for a short duration. In a reaction mechanism, intermediates can appear in the steps, but they cannot be reactants in the first step, as they must be formed from reactants.
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Reaction Energy Profile
A reaction energy profile is a graphical representation of the energy changes that occur during a chemical reaction. It typically shows the energy of reactants, products, and intermediates along the reaction coordinate. Intermediates are represented as valleys in the diagram, indicating lower energy states compared to the transition states, which are depicted as peaks.
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Related Practice
Textbook Question
(b) What is the difference between a unimolecular and a bimolecular elementary reaction?
Textbook Question
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (a) Cl2(g) → 2 Cl(g)
Textbook Question
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (b) OCl-(aq + H2O(l) → HOCl(aq) + OH-(aq)
Textbook Question
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (c) NO(g) + Cl2(g) → NOCl2(g)