   Chapter 15, Problem 72SCQ

Chapter
Section
Textbook Problem

The size of a flask containing colorless N2O4(g) and brown NO2(g) at equilibrium is rapidly reduced to half the original volume.N2O4(g) ⇄ 2 NO2(g) (a) What color change (if any) is observed immediately upon halving the flask size? (b) What color change (if any) is observed during the process in which equilibrium is reestablished in the flask?

(a)

Interpretation Introduction

Interpretation:

The colour change occurs in the equilibrium of N2O42NO2 when the volume is reduced to half the original has to be identified.

Concept Introduction:

Le Chatelier’s principle: If equilibrium is disturbed by changing conditions, the system will moves the equilibrium to reverse the change.

Factor’s that effect chemical equilibria:

• Concentration – Equilibrium will be affected by changing the concentration of reactant or product. If we increase the concentration of reactant system will try to reverse the change by favouring forward reaction and thus increase the concentration of products. Likewise adding products increase yield of reactants.
• Temperature – When the temperature increases equilibrium will shift in the endothermic direction, in the direction that absorbs heat. When the temperature decreases equilibrium will shift in the exothermic direction, in the direction that releases heat.
• Pressure and volume – If the reaction consists of only liquid and solid reactants and products, pressure has no effect in the equilibrium.

In gas reactions if the number of moles has no change then there will be no effect by pressure on equilibrium.

If pressure increases (volume decreases) then equilibrium will shift to the direction having less number of molecules and if pressure decreases (volume increases) system will shift to the direction having more number of molecules.

Explanation

Given reaction:

N2O42NO2colourlessȀ

(b)

Interpretation Introduction

Interpretation:

The colour change during the reestablishment of equilibrium has to be identified.

Concept Introduction:

Le Chatelier’s principle: If equilibrium is disturbed by changing conditions, the system will moves the equilibrium to reverse the change.

Factor’s that effect chemical equilibria:

• Concentration – Equilibrium will be affected by changing the concentration of reactant or product. If we increase the concentration of reactant system will try to reverse the change by favouring forward reaction and thus increase the concentration of products. Likewise adding products increase yield of reactants.
• Temperature – When the temperature increases equilibrium will shift in the endothermic direction, in the direction that absorbs heat. When the temperature decreases equilibrium will shift in the exothermic direction, in the direction that releases heat.
• Pressure and volume – If the reaction consists of only liquid and solid reactants and products, pressure has no effect in the equilibrium.

In gas reactions if the number of moles has no change then there will be no effect by pressure on equilibrium.

If pressure increases (volume decreases) then equilibrium will shift to the direction having less number of molecules and if pressure decreases (volume increases) system will shift to the direction having more number of molecules.

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