Chapter 15, Problem 60GQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# Nitrosyl bromide, NOBr, dissociates readily at room temperature.NOBr(g) ⇄ NO(g) + ½ Br2(g)Some NOBr is placed in a flask at 25 °C and allowed to dissociate. The total pressure at equilibrium is 190 mm Hg and the compound is found to be 34% dissociated. What is the value of Kp?

Interpretation Introduction

Interpretation:

The Kp for the dissociation reaction of NOBr when the total pressure is 190mmHg has to be calculated.

Concept Introduction:

Equilibrium constant in terms of pressure[Kp]: Equilibrium constant can be expressed in terms of partial pressures in atmospheres.

aA(g)+bB(g)cC(g)+dD(g)KP=PCc×PDdPAa×PBb

The activity of solid substance will not appear in equilibrium and numerically it is considered as one.

Explanation

Given:

NOBr(g)â€‰â‡„â€‰â€‰â€‰NOâ€‰(g)+â€‰12Br2â€‰(g)Totalâ€‰pressureâ€‰=â€‰190â€‰mmâ€‰Hgâ€‰â€‰=â€‰0.25â€‰atm34%â€‰ofâ€‰NOBrâ€‰isâ€‰dissociatedTemperatureâ€‰â€‰â€‰â€‰=â€‰â€‰25Â°Câ€‰â€‰â€‰â€‰â€‰â€‰â€‰=â€‰â€‰298â€‰K

The partial pressures of gases are directly proportional to the number of moles, hence we can use pressures instead of moles.

NOBr(g)â€‰â‡„â€‰â€‰â€‰NOâ€‰(g)+â€‰12Br2â€‰(g). This equation can be re-written as â€‰â€‰2NOBr(g)â€‰â‡„â€‰â€‰â€‰2NOâ€‰(g)+â€‰Br2â€‰(g)

â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰2NOBr(g)â€‰â‡„â€‰â€‰â€‰2NOâ€‰(g)+â€‰Br2â€‰(g)Initialâ€‰pressureâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰xâ€‰atmâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰Ifâ€‰34%â€‰ofâ€‰NOBrâ€‰isâ€‰dissociated,â€‰thenâ€‰â€‰â€‰-0.34â€‰xâ€‰isâ€‰consumedEquilibriumâ€‰pressureâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰0

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