   Chapter 15, Problem 38GQ

Chapter
Section
Textbook Problem

At 2300 K the equilibrium constant for the formation of NO(g) is 1.7 × 10−3.N2(g) + O2(g) ⇄ 2 NO(g) (a) Analysis shows that the concentrations of N2 and O2 are both 0.25 M, and that of NO is 0.0042 M under certain conditions. Is the system at equilibrium? (b) If the system is not at equilibrium, in which direction does the reaction proceed? (c) When the system is at equilibrium, what are the equilibrium concentrations?

(a)

Interpretation Introduction

Interpretation: The given system is whether at equilibrium has to be identified.

Concept introduction:

• Equilibrium constant: At equilibrium the ratio of products to reactants has a constant value. And it is represented by the letter K.

For a general reaction, aA+bBcC+dD

The equilibrium constant Kc=[C]c[D]d[A]a[B]b    a, b, c and d are the stoichiometric coefficients of reactant and product in the reaction. Concentration value for solid substance is 1.

If the value of Kc and the concentration of any of the reactant of a reaction is known then the concentration of product can be determined by multiplying Kc with the concentration of reactant.

• Reaction quotient Q expresses the relative ratio of product to reactants at a given instant. Using either the initial concentration of all components of the reaction, the progression of a reaction can easily be determined.

For a general reaction, aA+bBcC+dD

Reaction quotient   Q=[C]c[D]d[A]a[B]b

When Q=K the system is at equilibrium and there is no shift to either the left or the right.

When Q<K there are more reactants than products. Therefore some of the reactants will become products, causing the reaction to the right.

When Q>K  there are more products than reactants. To decrease the amount of products, the reaction will shift to the left and produce more reactant.

Explanation

To check: The system is equilibrium or not.

The balanced equation for the formation of NO is,

N2(g)+O2(g)2NO(g)

The concentration of N2andO2 are both 0.25M and that of NO is 0.0042M.

The reaction quotient Q for this reaction is,

Q=[NO]2[N2][O2]=(0

(b)

Interpretation Introduction

Interpretation: The direction in which the reaction proceeds if the system is not at equilibrium should be determined.

Concept introduction:

• Equilibrium constant: At equilibrium the ratio of products to reactants has a constant value. And it is represented by the letter K.

For a general reaction, aA+bBcC+dD

The equilibrium constant Kc=[C]c[D]d[A]a[B]b   a, b, c and d are the stoichiometric coefficients of reactant and product in the reaction. Concentration value for solid substance is 1.

If the value of Kc and the concentration of any of the reactant of a reaction is known then the concentration of product can be determined by multiplying Kc with the concentration of reactant.

• Reaction quotient Q expresses the relative ratio of product to reactants at a given instant. Using either the initial concentration of all components of the reaction, the progression of a reaction can easily be determined.

For a general reaction, aA+bBcC+dD

Reaction quotient   Q=[C]c[D]d[A]a[B]b

When Q=K the system is at equilibrium and there is no shift to either the left or the right.

When Q<K there are more reactants than products. Therefore some of the reactants will become products, causing the reaction to the right.

When Q>K  there are more products than reactants. To decrease the amount of products, the reaction will shift to the left and produce more reactant.

• ICE (reaction initial concentration equilibrium) table is mainly used to calculate the value of K for a reaction. This table contains the concentration of reactant and product in various stage of reaction.

(c)

Interpretation Introduction

Interpretation: The equilibrium constant when the system is at equilibrium should be determined.

Concept introduction:

• Equilibrium constant: At equilibrium the ratio of products to reactants has a constant value. And it is represented by the letter K.

For a general reaction, aA+bBcC+dD

The equilibrium constant Kc=[C]c[D]d[A]a[B]b    a, b, c and d are the stoichiometric coefficients of reactant and product in the reaction. Concentration value for solid substance is 1.

If the value of Kc and the concentration of any of the reactant of a reaction is known then the concentration of product can be determined by multiplying Kc with the concentration of reactant.

• Reaction quotient Q expresses the relative ratio of product to reactants at a given instant. Using either the initial concentration of all components of the reaction, the progression of a reaction can easily be determined.

For a general reaction, aA+bBcC+dD

Reaction quotient   Q=[C]c[D]d[A]a[B]b

When Q=K the system is at equilibrium and there is no shift to either the left or the right.

When Q<K there are more reactants than products. Therefore some of the reactants will become products, causing the reaction to the right.

When Q>K  there are more products than reactants. To decrease the amount of products, the reaction will shift to the left and produce more reactant.

• ICE (reaction initial concentration equilibrium) table is mainly used to calculate the value of K for a reaction. This table contains the concentration of reactant and product in various stage of reaction.

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