Chapter 19, Problem 19.140QP

 (a)

Interpretation Introduction

Interpretation:

The EMF of given voltaic cell should be calculated by using standard free energy changes of reactants and products.

Concept introduction:

Free energy change:

In thermodynamics the cell potential is known as  maximum work of the cell and it is equal to free energy change of the cell and it is given by,

$\text{ΔG}\text{=}{\text{-nFE}}_{\text{cell}}$

Where,

$\begin{array}{l}\text{ΔG}\text{is}\text{free}\text{energy}\text{change}\\ \text{n}\text{is}\text{number}\text{of}\text{electron}\text{transferred}\\ \text{F}\text{is}\text{faraday constant}\\ {\text{E}}_{\text{cell}}\text{is}\text{cell potential}\end{array}$

Free energy change:

The free energy change of a reaction is given by the subtraction of free energy changes of reactants from free energy changes of reactants.

$\text{ΔG}\text{=}{{\displaystyle \sum {\text{nΔG}}_{\text{f}}}}^{\text{°}}\text{(products)-}{{\displaystyle \sum {\text{mΔG}}_{\text{f}}}}^{\text{°}}\text{(reactants)}$

(b)

Interpretation Introduction

Interpretation:

Equilibrium constant of given reaction should be calculated.

Concept introduction:

Equilibrium constant ${\text{K}}_{\text{c}}$:

The relationship between equilibrium constant and cell potential (EMF) is given by below equation

${\text{E}}_{\text{cell}}\text{=}\frac{0.0592}{\text{nF}}\text{log}{\text{K}}_{\text{c}}$

Where,

$\begin{array}{l}{\text{K}}_{\text{c}}\text{is}\text{equilibrium constant}\\ \text{n}\text{is}\text{number}\text{of}\text{electron}\text{transferred}\\ \text{F}\text{is}\text{faraday constant}\\ {\text{E}}_{\text{cell}}\text{is}\text{cell potential}\end{array}$

(c)

Interpretation Introduction

Interpretation:

The effect of concentration of ${\text{Fe}}_{\text{(aq)}}^{2+}$ ion on equilibrium constant should be explained.

Equilibrium constant ${\text{K}}_{\text{c}}$:

The relationship between equilibrium constant and cell potential (EMF) is given by below equation

${\text{E}}_{\text{cell}}\text{=}\frac{0.0592}{\text{nF}}\text{log}{\text{K}}_{\text{c}}$

Where,

$\begin{array}{l}{\text{K}}_{\text{c}}\text{is}\text{equilibrium constant}\\ \text{n}\text{is}\text{number}\text{of}\text{electron}\text{transferred}\\ \text{F}\text{is}\text{faraday constant}\\ {\text{E}}_{\text{cell}}\text{is}\text{cell potential}\end{array}$