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Ch.14 - Chemical Kinetics
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
Chapter 14, Problem 86

Why don't all collisions between reactant molecules lead to a chemical reaction?

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insert step 1> Understand that not all collisions between reactant molecules result in a chemical reaction due to the concept of collision theory.
insert step 2> According to collision theory, for a reaction to occur, reactant molecules must collide with sufficient energy, known as the activation energy, to break bonds and form new ones.
insert step 3> Recognize that molecules must also collide with the correct orientation to allow the necessary rearrangement of atoms and formation of products.
insert step 4> Consider that even if molecules collide with the right orientation, if they do not have enough kinetic energy to overcome the activation energy barrier, the reaction will not proceed.
insert step 5> Realize that factors such as temperature, concentration, and the presence of a catalyst can influence the frequency and energy of collisions, thereby affecting the likelihood of a reaction occurring.

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Key Concepts

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

Collision Theory

Collision theory posits that for a chemical reaction to occur, reactant molecules must collide with sufficient energy and proper orientation. Not all collisions result in a reaction because only those that meet these criteria can overcome the activation energy barrier, which is the minimum energy required for the reactants to transform into products.
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Activation Energy

Activation energy is the energy threshold that must be surpassed for a reaction to proceed. It represents the energy needed to break bonds in the reactants and form new bonds in the products. If the energy of the colliding molecules is below this threshold, the collision will not result in a reaction, regardless of how frequently collisions occur.
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Molecular Orientation

Molecular orientation refers to the specific alignment of reactant molecules during a collision. For a reaction to occur, the molecules must collide in a way that allows for the effective overlap of their electron clouds, facilitating bond formation. If the orientation is incorrect, even a collision with sufficient energy may not lead to a successful reaction.
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Related Practice
Textbook Question
What fraction of the molecules in a gas at 300 K collide with an energy equal to or greater than Ea when Ea equals 50 kJ/mol? What is the value of this fraction when Ea is 100 kJ/mol?
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Textbook Question

Consider the following concentration–time data for the decomposition reaction AB → A + B.

(b) What is the molarity of AB after a reaction time of 192 min?

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Textbook Question
Trans-cycloheptene 1C7H122, a strained cyclic hydrocarbon, converts to cis-cycloheptene at low temperatures. This molecular rearrangement is a second-order process with a rate constant of 0.030 M-1 s-1 at 60 °C. If the initial concentration of trans-cycloheptene is 0.035 M: (c) What is the half-life of trans-cycloheptene at an initial concentration of 0.075 M?
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Textbook Question

Consider the following concentration–time data for the decomposition reaction AB → A + B.

(a) Determine the order of the reaction and the value of the rate constant.

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Textbook Question

Consider three reactions with different values of Ea and ΔE:

Reaction 1. Ea = 20 kJ>mol; ΔE = -60 kJ/mol

Reaction 2. Ea = 10 kJ>mol; ΔE = -20 kJ/mol

Reaction 3. Ea = 40 kJ>mol; ΔE = +15 kJ/mol

(b) Assuming that all three reactions are carried out at the same temperature and that all three have the same frequency factor A, which reaction is the fastest and which is the slowest?

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Textbook Question
Two reactions have the same activation energy, but their rates at the same temperature differ by a factor of 10. Explain.
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