   # At 25°C. K p ≈ 1 × 10 −31 for the reaction a . Calculate the concentration of NO, in molecules/cm 3 , that can exist in equilibrium in air at 25°C. In air, P N 2 = 0.8 atm and P O 2 = 0.2 atm. b . Typical concentrations of NO in relatively pristine environments range from 10 8 to 10 10 molecules/cm 3 Why is there a discrepancy between these values and your answer to part a? ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 12, Problem 74AE
Textbook Problem
3 views

## At 25°C. Kp ≈1 × 10−31 for the reactiona. Calculate the concentration of NO, in molecules/cm3, that can exist in equilibrium in air at 25°C. In air, P N 2 = 0.8 atm and P O 2 = 0.2 atm.b . Typical concentrations of NO in relatively pristine environments range from 108 to 1010 molecules/cm3 Why is there a discrepancy between these values and your answer to part a?

(a)

Interpretation Introduction

Interpretation: The equilibrium constant and reaction of production of NO is given. The concentration of NO (inmolecules/cm3) for the given values of pressure of reactant is to be calculated. Also the reason of discrepancy between the calculated and theoretical value of concentration of NO is to be given.

Concept introduction: The state when the reactants involved in a chemical reaction and the products formed in the reaction exist in concentrations having no further tendency to change is known as an equilibrium state of the reaction. When the equilibrium constant is represented as K .

To determine: The concentration of NO (inmolecules/cm3) for the given reaction.

### Explanation of Solution

Explanation

Given

The given temperature is 25°C .

The equilibrium constant is 1.0×1031 .

The initial pressure of reactant is,

(PO2)=0.2atm(PN2)=0.8atm

The initial pressure is assumed to be initial concentration.

The stated reaction is,

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

The conversion of degree Celsius (°C) into Kelvin (K) is done as,

T(K)=T(°C)+273

Hence,

The conversion of 25°C into Kelvin is,

T(K)=T(°C)+273T(K)=(25+273)K=298K

At equilibrium, the equilibrium ratio is expressed by the formula,

Kp=ConcentrationofproductsConcentrationofreactants

Where,

• Kp is the equilibrium constant.

The equilibrium ratio for the given reaction is,

Kp=(PNO)2(PO2)(PN2)

Substitute the values of Kp,(PO2) and (PN2) in the above expression.

Kp=(PNO)2(PO2)(PN2)1×1031=(PNO)2(0.8)(0.2)(PNO)=1

(b)

Interpretation Introduction

Interpretation: The equilibrium constant and reaction of production of NO is given. The concentration of NO (inmolecules/cm3) for the given values of pressure of reactant is to be calculated. Also the reason of discrepancy between the calculated and theoretical value of concentration of NO is to be given.

Concept introduction: The state when the reactants involved in a chemical reaction and the products formed in the reaction exist in concentrations having no further tendency to change is known as an equilibrium state of the reaction. When the equilibrium constant is represented as K .

To determine: The reason of discrepancy between the calculated and theoretical value of concentration of NO .

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