Concept explainers
Show a sketch of a galvanic concentration cell. Each compartment consists of a Co electrode in a Co(NO3)2 solution. The concentrations in the compartments are 2.0 M and 0.10 M, respectively. Label the anode and cathode compartments. Show the direction of electron flow. (a) Calculate the Ecell at 25°C. (b) What are the concentrations in the compartments when the Ecell drops to 0.020 V? Assume volumes to remain constant at 1.00 L in each compartment.
a)
Interpretation:
A
Concept introduction:
Standard reduction potential: The voltage associated with a reduction reaction at an electrode when all solutes are 1M and all gases are at 1 atm. The hydrogen electrode is called the standard hydrogen electrode (SHE).
Standard emf:
Where both
Thermodynamics of redox reactions:
The change in free-energy represents the maximum amount of useful work that can be obtained in a reaction:
Relation between
Relation between
Effect of concentration on cell Emf:
The mathematical relationship between the emf of galvanic cell and the concentration of reactants and products in a redox reaction under nonstandard-state conditions is,
As known
Dividing by –nF, the above equation becomes,
Nernst equation: The Nernst equation is used to calculate the cell voltage under nonstandard-state conditions.
Explanation of Solution
Figure.1
A galvanic concentration cell, each compartment consists of Co electrode in
Nernst equation of the concentration cell and Substitute known constant values of R, T and F into Nernst equation becomes as follows,
The number of electrons transferred in the given redox reaction is TWO (n=2) and
The emf of the given galvanic cell reaction is
b)
Interpretation:
The concentrations in the compartments when
Concept introduction:
Standard reduction potential: The voltage associated with a reduction reaction at an electrode when all solutes are 1M and all gases are at 1 atm. The hydrogen electrode is called the standard hydrogen electrode (SHE).
Standard emf:
Where both
Thermodynamics of redox reactions:
The change in free-energy represents the maximum amount of useful work that can be obtained in a reaction:
Relation between
Relation between
Effect of concentration on cell Emf:
The mathematical relationship between the emf of galvanic cell and the concentration of reactants and products in a redox reaction under nonstandard-state conditions is,
As known
Dividing by –nF, the above equation becomes,
Nernst equation: The Nernst equation is used to calculate the cell voltage under nonstandard-state conditions.
Explanation of Solution
As a concentration cell runs, the concentration of the two solutions approaches each other. Let concentration of the dilute solution equal
The number of electrons transferred in the given redox reaction is TWO (n=2) and
Solve for x as follows,
At anode compartment:
At cathode compartment:
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Chapter 18 Solutions
Chemistry
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