   Chapter 19, Problem 35PS

Chapter
Section
Textbook Problem

Calculate ΔrG° and the equilibrium constant for the following reactions. (a) 2 Fe3+(aq) + 2 I−(aq) ⇄ 2 Fe2+(aq) + I2(aq) (b) I2(aq) + 2 Br−(aq) ⇄ 2 I−(aq) + Br2(ℓ)

a)

Interpretation Introduction

Interpretation:

The ΔrGo value and the equilibrium constant for the following reaction has to determined.

1. a) 2Fe3+(aq) + 2I-(aq)2Fe2+(aq) + I2(aq)

Concept introduction:

According to the first law of thermodynamics, the change in internal energy of a system is equal ti the heat added to the sysytem minus the work done by the system.

The equation is as follows.

ΔU = Q - WΔU = Change in internal energyQ = Heat added to the systemW=Work done by the system

In voltaic cell, the maximum cell potential is directly related to the free energy difference between the reactants and products in the cell.

ΔG0= -nFE0n = Number of moles transferred per mole of reactant and productsF = Faradayconstant=96485C/mol  E0= Volts = Work(J)/Charge(C)

The relation between standard cell potential and equilibrium constant is as follows.

lnK = nE00.0257 at 298K

Explanation

The given chemical reaction is as follows.

2Fe3+(aq) + 2I-(aq)2Fe2+(aq) + I2(aq)

Let’s write an each half cell reaction.

At anode:Oxiation : I2(l) + 2e  2I(aq)At cathode:Reduction : 2Fe3+(aq) + 2e2Fe2+(aq)

Let’s calculate the Ecello value of the reaction.

Ecello= ECathode0- EAnode0= 0.771  V-(-0.535 V)= 0.236 V

Let’s calculate the ΔG0 value for the reaction

(b)

Interpretation Introduction

Interpretation:

The ΔrGo value and the equilibrium constant for the following reaction has to be determined.

1. a) I2(aq) + 2Br-(aq)2I-(aq) + Br2(l)

Concept introduction:

According to the first law of thermodynamics, the change in internal energy of a system is equal ti the heat added to the sysytem minus the work done by the system.

The equation is as follows.

ΔU = Q - WΔU = Change in internal energyQ = Heat added to the systemW=Work done by the system

In voltaic cell, the maximum cell potential is directly related to the free energy difference between the reactants and products in the cell.

ΔG0= -nFE0n = Number of moles transferred per mole of reactant and productsF = Faradayconstant=96485C/mol  E0= Volts = Work(J)/Charge(C)

The relation between standard cell potential and equilibrium constant is as follows.

lnK = nE00.0257 at 298K

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