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Ch.14 - Chemical Kinetics
Chapter 14, Problem 120e

The gas-phase reaction of NO with F2 to form NOF and F has an activation energy of Ea = 6.3 kJ>mol. and a frequency factor of A = 6.0 * 108 M-1 s-1. The reaction is believed to be bimolecular: NO1g2 + F21g2 ¡ NOF1g2 + F1g2 (e) Suggest a reason for the low activation energy for the reaction.

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Identify the key components of the reaction: The reactants are NO and F2, and the products are NOF and F. The reaction is bimolecular, involving two molecules colliding.
Understand the concept of activation energy (Ea): Activation energy is the minimum energy required for a reaction to occur. It is the energy barrier that reactants must overcome to be transformed into products.
Analyze the given activation energy value: An activation energy of 6.3 kJ/mol is relatively low, which suggests that the energy barrier for this reaction is not very high.
Consider the nature of the reactants: NO is a radical with an unpaired electron, and F2 is a molecule that can easily dissociate into radicals. The presence of radicals generally leads to lower activation energies because radicals are highly reactive and can stabilize transition states.
Propose a reason for the low activation energy: The low activation energy could be due to the formation of a transient intermediate or transition state that is stabilized by the radical nature of the reactants, leading to a more efficient reaction pathway with a lower energy barrier.

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Key Concepts

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

Activation Energy

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. A low activation energy, such as 6.3 kJ/mol in this reaction, indicates that the reaction can proceed relatively easily, often due to favorable molecular interactions or the presence of a catalyst.
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Bimolecular Reactions

Bimolecular reactions involve two reactant molecules colliding to form products. The rate of bimolecular reactions is influenced by the concentration of both reactants and the frequency of their collisions. In this case, the reaction between NO and F2 suggests that the low activation energy may be due to effective collisions between these two species, leading to a faster reaction rate.
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Frequency Factor

The frequency factor (A) is a term in the Arrhenius equation that reflects the frequency of collisions and the orientation of reactant molecules during those collisions. A high frequency factor, like 6.0 x 10^8 M^-1 s^-1, suggests that the reactants are colliding frequently and with the correct orientation, which can contribute to a lower activation energy by increasing the likelihood of successful reactions.
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Related Practice
Open Question
Dinitrogen pentoxide (N2O5) decomposes in chloroform as a solvent to yield NO2 and O2. The decomposition is first order with a rate constant at 45 _x001E_C of 1.0 * 10^-5 s^-1. Calculate the partial pressure of O2 produced from 1.00 L of 0.600 M N2O5 solution at 45 _x001E_C over a period of 20.0 h if the gas is collected in a 10.0-L container. (Assume that the products do not dissolve in chloroform.)
Textbook Question

The reaction between ethyl iodide and hydroxide ion in ethanol 1C2H5OH2 solution, C2H5I1alc2 + OH- 1alc2 ¡ C2H5OH1l2 + I - 1alc2, has an activation energy of 86.8 kJ>mol and a frequency factor of 2.10 * 1011 M-1 s-1. (c) Which reagent in the reaction is limiting, assuming the reaction proceeds to completion?

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Textbook Question

The reaction between ethyl iodide and hydroxide ion in ethanol 1C2H5OH2 solution, C2H5I1alc2 + OH- 1alc2 ¡ C2H5OH1l2 + I - 1alc2, has an activation energy of 86.8 kJ>mol and a frequency factor of 2.10 * 1011 M-1 s-1. (d) Assuming the frequency factor and activation energy do not change as a function of temperature, calculate the rate constant for the reaction at 50 C.

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Textbook Question

The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (a) Calculate the overall standard enthalpy change for the reaction process.

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Textbook Question

The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (c) Draw a plausible Lewis structure for the intermediate HOOBr. To what familiar compound of hydrogen and oxygen does it appear similar?

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Textbook Question

The rates of many atmospheric reactions are accelerated by the absorption of light by one of the reactants. For example, consider the reaction between methane and chlorine to produce methyl chloride and hydrogen chloride: Reaction 1: CH41g2 + Cl21g2 ¡ CH3Cl1g2 + HCl1g2 This reaction is very slow in the absence of light. However, Cl21g2 can absorb light to form Cl atoms: Reaction 2: Cl21g2 + hv ¡ 2 Cl1g2 Once the Cl atoms are generated, they can catalyze the reaction of CH4 and Cl2, according to the following proposed mechanism: Reaction 3: CH41g2 + Cl1g2 ¡ CH31g2 + HCl1g2 Reaction 4: CH31g2 + Cl21g2 ¡ CH3Cl1g2 + Cl1g2 The enthalpy changes and activation energies for these two reactions are tabulated as follows: Reaction H 1kJ ,mol 2 Ea 1kJ ,mol 2 3 +4 17 4 -109 4 (b) By using the data tabulated here, sketch a quantitative energy profile for the catalyzed reaction represented by reactions 3 and 4.

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