   Chapter 14, Problem 83GQ

Chapter
Section
Textbook Problem

Nitramide, NO2NH2, decomposes slowly in aqueous solution according to the following reaction:NO2NH2(aq) → N2O(g) + H2O(ℓ)The reaction follows the experimental rate law Rate= k[NO 2 NH 2 ] [H 3 O + ] (a) What is the apparent order of the reaction in a pH buffered solution? (In a pH buffered solution, the concentration of H3O+ is a constant.) (b) Which of the following mechanisms is the most appropriate for the interpretation of this rate law? Explain. (Note that when writing the expression for K, the equilibrium constant, [H2O] is not involved. See Chapter 15.) Mechanism 1 NO 2 NH 2 → K 1  N 2 O + H 2 O Mechanism 2 NO 2 NH 2 +H 3 O + ⇄ k 2 ′ k 2  NO 2 NH 3 +  + H 2 O (rapid equilibrium) NO 2 NH 3 + → k 3 N 2 O + H 3 O + (rate-limiting step) Mechanism 3 NO 2 NH 2 +H 2 O ⇄ k 4 ′ k 4  NO 2 NH − + H 3 O + (rapid equilibrium) NO 2 NH − → k 5 N 2 O+OH − (rate-limiting step) H 3 O + +OH − → k 6 2H 2 O (very fast reaction) (c) Show the relationship between the experimentally observed rate constant, k, and the rate constants in the selected mechanism. (d) Based on the experimental rate law, will the reaction rate increase or decrease if the pH of the solution is increased?

(a)

Interpretation Introduction

Interpretation:

Order of the reaction in pH buffered solution has to be determined.

Concept Introduction:

Rate order: The order of each reactant in a reaction is represented by the exponential term of the respective reactant present in the rate law and the overall order of the reaction is the sum of all the exponents of all reactants present in the chemical reaction.  The order of the reaction is directly proportional to the concentration of the reactants.

Rate law: It is generally the rate equation that consists of the reaction rate with the concentration or the pressures of the reactants and constant parameters.

Rate constant: The rate constant for a chemical reaction is the proportionality term in the chemical reaction rate law which gives the relationship between the rate and the concentration of the reactant present in the chemical reaction.

pH : It is used to measure the acidity of chemical substances present in water.  Increased pH means more H+ ions present in the solution.

Explanation

Examining the rate law shows that the order of reactant NO2NH2 is one and the order of H3O+ is -1

(b)

Interpretation Introduction

Interpretation:

The given mechanism is most appropriate for the interpretation of this rate law should be explained.

Concept Introduction:

Rate order: The order of each reactant in a reaction is represented by the exponential term of the respective reactant present in the rate law and the overall order of the reaction is the sum of all the exponents of all reactants present in the chemical reaction.  The order of the reaction is directly proportional to the concentration of the reactants.

Rate law: It is generally the rate equation that consists of the reaction rate with the concentration or the pressures of the reactants and constant parameters.

Rate constant: The rate constant for a chemical reaction is the proportionality term in the chemical reaction rate law which gives the relationship between the rate and the concentration of the reactant present in the chemical reaction.

(c)

Interpretation Introduction

Interpretation:

The relationship between experimentally observed rate constant and the rate constant in the selected mechanism has to be shown.

Concept Introduction:

Rate order: The order of each reactant in a reaction is represented by the exponential term of the respective reactant present in the rate law and the overall order of the reaction is the sum of all the exponents of all reactants present in the chemical reaction.  The order of the reaction is directly proportional to the concentration of the reactants.

Rate law: It is generally the rate equation that consists of the reaction rate with the concentration or the pressures of the reactants and constant parameters.

Rate constant: The rate constant for a chemical reaction is the proportionality term in the chemical reaction rate law which gives the relationship between the rate and the concentration of the reactant present in the chemical reaction.

(d)

Interpretation Introduction

Interpretation:

Either the reaction increase or decrease if the pH of the solution is increased has to be shown based on the experimental rate law.

Concept Introduction:

Rate order: The order of each reactant in a reaction is represented by the exponential term of the respective reactant present in the rate law and the overall order of the reaction is the sum of all the exponents of all reactants present in the chemical reaction.  The order of the reaction is directly proportional to the concentration of the reactants.

Rate law: It is generally the rate equation that consists of the reaction rate with the concentration or the pressures of the reactants and constant parameters.

Rate constant: The rate constant for a chemical reaction is the proportionality term in the chemical reaction rate law which gives the relationship between the rate and the concentration of the reactant present in the chemical reaction.

pH : It is used to measure the acidity of chemical substances present in water.  Increased pH means more H+ ions present in the solution.

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