CONTENTS
Electrochemistry: definition & importance
Conductors: metallic & electrolytic conduction,
Electrolytes, Electrochemical cell & electrolytic cell
A simple electrochemical cell: Galvanic cell or (Daniell Cell)
Cell reaction, cell representation, Salt bridge & its use,
Electrode potential, standard electrode potential, SHE,
Standard cell potential or standard electromotive force of a cell
Electrochemical series (Standard reduction potential values)
Nernst Equation, Relationship with Standard cell potential with Gibbs energy & also equilibrium constant
Resistance (R) & conductance (G) of a solution of an electrolyte
Conductivity (k) of solution, Cell constant (G*) & their units,
Molar conductivity (Λm) & its variation with concentration & temperature,
Debye Huckel Onsager equation & Limiting molar conductivity,
Kohlrausch’s law & its application & numerical problems.
Electrolytic cells & electrolysis.
Some examples of electrolysis of electrolytes in molten / aq. state.
Faraday’s laws of electrolysis: First & second law- numerical problems. Corrosion, Electrochemical theory of rusting.
Prevention of rusting.
Conductors and Non-Conductors
Substances can be classified as conductors and non-conductors based on their ability to conduct electricity.
Conductors: Substances that allow electric current to flow through them are called conductors. For example, Plastic, Wood, etc.
Non-Conductors: Non-conductors are insulators that do not allow electricity to pass through them. For example, Copper, Iron, etc.
Types of Conductors
Conductors are divided into two groups: Metallic conductors and Electrolytes.
Metallic Conductors: These conductors conduct electricity by the movement of electrons without any chemical change during the process. This type of conduction happens in solids and in the molten state.
Electrolytes: They conduct electricity by the movement of the ions in the solutions. It is present in the aqueous solution.
Distinguish between Metallic and Electrolytic Conduction
Metallic Conduction Electrolytic Conduction
The movement of electrons causes the electric current The movement of ions causes the electric current
There is no chemical reaction Ions get ionised or reduced at the electrodes
There is no transfer of matter It involves the transfer of matter in the form of ions
Follows Ohm’s law Follows Ohm’s law
Resistance increases with an increase in temperature Resistance decreases with an increase in temperature
Faraday’s law is not followed Follows Faraday’s law
Electrolytes
(a) Substances whose aqueous solutions allow the conductance of electric current and are chemically decomposed are called electrolytes.
(b) The positively charged ions furnished by the electrolyte are called cations, while the negatively charged ions furnished by the electrolyte are called anions.
Types of Electrolytes
(a) Weak electrolytes: Electrolytes that are decomposable to a very small extent in their dilute solutions are called weak electrolytes. For example, organic acids, inorganic acids and bases etc.
(b) Strong electrolytes: Electrolytes that are highly decomposable in aqueous solution and conduct electricity frequently are called electrolytes. For example, mineral acid and salts of strong acid.
Electrode
For the electric current to pass through an electrolytic conductor, the two rods or plates called electrodes are always needed. These plates are connected to the terminals of the battery to form a cell. The electrode through which the electric current flows into the electrolytic solution is called the anode, also called the positive electrode, and anions are oxidised here.
An electrode through which the electric current flows out of the electrolytic solution is called the cathode, also called the negative electrode, and cations are reduced there.
Electrolysis
Electrolysis is the process of chemical deposition of the electrolyte by passing an electric current. Electrolysis takes place in an electrolytic cell. This cell will convert the electrical energy to chemical energy.
Electrochemistry is the study of electron movement in an oxidation or reduction reaction at a polarized electrode surface. Each analyte is oxidized or reduced at a specific potential and the current measured is proportional to concentration. This technique is a powerful methodology towards bioanalysis.
https://www.sciencedirect.com › ele...
Electrochemistry - an overv
To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.
CONTENTS
Electrochemistry: definition & importance
Conductors: metallic & electrolytic conduction,
Electrolytes, Electrochemical cell & electrolytic cell
A simple electrochemical cell: Galvanic cell or (Daniell Cell)
Cell reaction, cell representation, Salt bridge & its use,
Electrode potential, standard electrode potential, SHE,
Standard cell potential or standard electromotive force of a cell
Electrochemical series (Standard reduction potential values)
Nernst Equation, Relationship with Standard cell potential with Gibbs energy & also equilibrium constant
Resistance (R) & conductance (G) of a solution of an electrolyte
Conductivity (k) of solution, Cell constant (G*) & their units,
Molar conductivity (Λm) & its variation with concentration & temperature,
Debye Huckel Onsager equation & Limiting molar conductivity,
Kohlrausch’s law & its application & numerical problems.
Electrolytic cells & electrolysis.
Some examples of electrolysis of electrolytes in molten / aq. state.
Faraday’s laws of electrolysis: First & second law- numerical problems. Corrosion, Electrochemical theory of rusting.
Prevention of rusting.
Conductors and Non-Conductors
Substances can be classified as conductors and non-conductors based on their ability to conduct electricity.
Conductors: Substances that allow electric current to flow through them are called conductors. For example, Plastic, Wood, etc.
Non-Conductors: Non-conductors are insulators that do not allow electricity to pass through them. For example, Copper, Iron, etc.
Types of Conductors
Conductors are divided into two groups: Metallic conductors and Electrolytes.
Metallic Conductors: These conductors conduct electricity by the movement of electrons without any chemical change during the process. This type of conduction happens in solids and in the molten state.
Electrolytes: They conduct electricity by the movement of the ions in the solutions. It is present in the aqueous solution.
Distinguish between Metallic and Electrolytic Conduction
Metallic Conduction Electrolytic Conduction
The movement of electrons causes the electric current The movement of ions causes the electric current
There is no chemical reaction Ions get ionised or reduced at the electrodes
There is no transfer of matter It involves the transfer of matter in the form of ions
Follows Ohm’s law Follows Ohm’s law
Resistance increases with an increase in temperature Resistance decreases with an increase in temperature
Faraday’s law is not followed Follows Faraday’s law
Electrolytes
(a) Substances whose aqueous solutions allow the conductance of electric current and are chemically decomposed are called electrolytes.
(b) The positively charged ions furnished by the electrolyte are called cations, while the negatively charged ions furnished by the electrolyte are called anions.
Types of Electrolytes
(a) Weak electrolytes: Electrolytes that are decomposable to a very small extent in their dilute solutions are called weak electrolytes. For example, organic acids, inorganic acids and bases etc.
(b) Strong electrolytes: Electrolytes that are highly decomposable in aqueous solution and conduct electricity frequently are called electrolytes. For example, mineral acid and salts of strong acid.
Electrode
For the electric current to pass through an electrolytic conductor, the two rods or plates called electrodes are always needed. These plates are connected to the terminals of the battery to form a cell. The electrode through which the electric current flows into the electrolytic solution is called the anode, also called the positive electrode, and anions are oxidised here.
An electrode through which the electric current flows out of the electrolytic solution is called the cathode, also called the negative electrode, and cations are reduced there.
Electrolysis
Electrolysis is the process of chemical deposition of the electrolyte by passing an electric current. Electrolysis takes place in an electrolytic cell. This cell will convert the electrical energy to chemical energy.
Electrochemistry is the study of electron movement in an oxidation or reduction reaction at a polarized electrode surface. Each analyte is oxidized or reduced at a specific potential and the current measured is proportional to concentration. This technique is a powerful methodology towards bioanalysis.
https://www.sciencedirect.com › ele...
Electrochemistry - an overv
To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.To develop a premier world class education centre, for creating global project management professionals, thereby making Larsen & Toubro (L&T) a centre of excellence in project management.
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
4. Chemistry
18CYB101J
At anode: Zn (s) Zn2+ (aq.) + 2 e- (oxidation)
At cathode: Cu2+ (aq.) + 2e- Cu (s) (Reduction)
Net reaction: Zn (s) + Cu 2+ (aq.) Zn2+ (aq.) + Cu (s)
5. Chemistry
18CYB101J
Electrochemical Cells
An electrochemical cell consists of two electrodes, or metallic conductors, in contact with an electrolyte, an ionic
conductor (which may be a solution, a liquid, or a solid).
An electrode and its electrolyte comprise an electrode compartment. The two electrodes may share the same
compartment. If the electrolytes are different, the two compartments may be joined by a salt bridge, which is a tube
containing a concentrated electrolyte solution (almost always potassium chloride in agar jelly) that completes the
electrical circuit and enables the cell to function.
There are two types of electrochemical cells:
1. Galvanic cells
2. Electrolytic cells
• Both types contain two electrodes, which are solid metals connected to an external circuit that provides an electrical
connection between the two parts of the system
• The oxidation half-reaction occurs at one electrode (the anode), and the reduction half-reaction occurs at the other
(the cathode). When the circuit is closed, electrons flow from the anode to the cathode. The electrodes are also
connected by an electrolyte, an ionic substance or solution that allows ions to transfer between the electrode
compartments, thereby maintaining the system’s electrical neutrality.
6. Chemistry
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Galvanic and Electrolytic Cells
A galvanic cell (left)
transforms the energy released
by a spontaneous redox
reaction into electrical energy.
The oxidative and reductive
half-reactions occur in separate
compartments that are
connected by an external
electrical circuit; in addition, a
second connection that allows
ions to flow between the
compartments (shown here as a
vertical dashed line to
represent a porous barrier) is
necessary to maintain electrical
neutrality. The potential
difference between the
electrodes causes electrons to
flow from the reductant to
the oxidant through the
external circuit, generating an
electric current.
In an electrolytic cell
(right), an external source
of electrical energy is used
to generate a potential
difference between the
electrodes that forces
electrons to flow, driving
a nonspontaneous redox
reaction; only a single
compartment is employed
in most applications. In
both kinds of
electrochemical cells, the
anode is the electrode at
which the oxidation half-
reaction occurs, and the
cathode is the electrode at
which the reduction half-
reaction occurs
Fig. Electrochemical Cells
7. Chemistry
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Electrolytic Cell vs Galvanic Cell
At anode: Cl- ½ Cl2 (g) + e-
At cathode: Na+ + e- Na
At anode: Zn (s) Zn2+ (aq.) + 2 e-, E0 = 0.76 V
At cathode: Cu2+ (aq.) + 2e- Cu (s), E0 = 0.34 V
Net reaction: Zn (s) + Cu 2+ (aq.) Zn2+ (aq.) + Cu (s)
The cell potential, Ecell = 0.34 + 0.76 = 1.1 V
8. Chemistry
18CYB101J
Electrolytic cell Electrochemical cell
Electrical energy is converted to chemical energy Chemical energy is converted into electrical
energy
An input of energy is required for the redox
reactions to proceed in these cells, i.e. the
reactions are non-spontaneous
The redox reactions that take place in these cells
are spontaneous in nature
Anode is positive and cathode is negative
electrode
Anode is negative and cathode is positive
electrode
The external battery supplies the electrons. The
electrons enter through the cathode and come out
through the anode
The electrons are supplied by species getting
oxidized. They move from anode to the cathode
in the external circuit
9. Types of Reversible Electrodes
1. Metal-Metal ion electrodes: A metal rod dipped in a solution containing its own ions
e.g., A Zn rod dipped in a solution of zinc sulphate
Electrode reaction: Mz+ (aq) + z e- M (s)
2. Gas electrodes
e.g., Hydrogen electrode
Hydrogen gas bubbled in a solution of an acid (HCl) forms this type of electrode.
H+ (aq) + e- H2 (g)
3. Metal- insoluble metal salt electrodes
A metal and a sparingly soluble salt of the same metal dipped in a solution of a soluble salt
having the same anion
e.g., Calomel electrode consists of mercury, mercurous chloride (Hg2Cl2 (s)) and a solution of
potassium chloride
Hg2Cl2 (s) + e- 2 Hg (l) + 2 Cl- (aq)
4. Redox electrodes
The potential is developed in these electrodes due to the presence of ions of the same
substance in two different valence states
e.g., A platinum wire inserted in a solution containing Fe2+ and Fe3+ ions
Fe3+ (aq) + e- Fe2+ (aq)
Chemistry
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10. Chemistry
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Cell Notation
• The anode is written on the left hand side and it is represented by writing metal or solid phase first and then the metal
ions. The two are separated by semicolon or a vertical line.
Eg., Zn(s); Zn2+ (aq) or Zn(s) Zn2+(aq)
• The cathode is written on the right hand and it is
represented by writing metal ions first and the metal.
The two are separated by semicolon or vertical line.
Eg., Cu2+(aq);Cu(s) or Cu2+ Cu(s)
• When a salt bridge is used, it is indicated by two vertical lines separating the two half cells
Eg., Anode Cathode
• The above convention is used as
Eg., Zn(s); Zn2+ (aq) Cu2+(aq);Cu(s)
Fig. A cell diagram
11. Representation of the Cell (Galvanic Cell)
The electrode on the right is written in the order:
Ion, electrode (e.g., Cu2+, Cu) (involving reduction)
e.g., Cu2+ (aq) + 2e- Cu (s)
The electrode on the left is written in the order:
Electrode, ion (e.g., Zn, Zn2+) (involving oxidation)
e.g., Zn (s) Zn2+ (aq) + 2e -
The net reaction: Cu2+ (aq) + Zn (s) Cu(s) + Zn2+ (aq)
Thus, the galvanic cell can be represented as:
Zn (s), Zn2+ (aq) / Cu2+ (aq), Cu (s)
Chemistry
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12. Chemistry
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The cell potential, Ecell, is the measure of the potential difference between two half cells in an
electrochemical cell. The potential difference is caused by the ability of electrons to flow from one half cell
to the other.
Electrons are able to move between electrodes because the chemical reaction is a redox reaction. A redox
reaction occurs when a certain substance is oxidized, while another is reduced.
During oxidation, the substance loses one or more electrons, and thus becomes positively charged.
Conversely, during reduction, the substance gains electrons and becomes negatively charged.
This relates to the measurement of the cell potential because the difference between the potential for the
reducing agent to become oxidized and the oxidizing agent to become reduced will determine the cell
potential.
The cell potential (Ecell) is measured in voltage (V), which allows us to give a certain value to the cell
potential.
Cell Potential
15. The half-cell reaction with a lower reduction potential is
subtracted from the one with a higher electrode potential if both
half cell reactions are presented as reduction reactions.
(i) Cu2+ (aq) + 2e- Cu (s); Eel
0 = 0.34 V
(ii) Zn (s) Zn2+ (aq) + 2e- Eel
0 = -0.76 V
Subtracting Eq. (ii) from Eq. (i), we get
Cu2+ (aq) + Zn (s) Cu(s) + Zn2+ (aq)
The cell potential, Ecell
0 = 0.34 – (- 0.76) V
= 1.10 V
Determination of Cell Potential
Chemistry
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18. Chemistry
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Relationship between Cell Potentials and Free Energy
The maximum cell potentials is directly related to the free energy difference between the reactants and the products in
the cell
∆G = -nFE0 ........................ (1)
where, G – Gibbs free energy
n – No of moles transferred per mole of reactant and product
F – Faraday=96,485 coulombs
E0 – Standard potential
The equation (1) is derived by terms of
The maximum amount of work that can be produced by an electrochemical cell, Wmax, is equal to the product of the
cell potential,E0, and total charge transferred during the reaction
Wmax = -nFE0 ....................... (2)
Work is expressed as a negative number because work is being done by the system on the surroundings.
∆G0 is also the measure of the maximum amount of work that can be performed during chemical reaction (∆G=Wmax
there must be a relationship between the potential of an electrochemical cell and the change in free energy, ∆G
∆G0 = -nFE0
19. Chemistry
18CYB101J
Nernst Equation
Gibb's Free Energy
The Gibb's free energy G is the negative value of maximum electric work,
∆G = - W
= - q ∆E
A redox reaction equation represents definite amounts of reactants in the formation of also definite amounts of products.
The number (n) of electrons in such a reaction equation, is related to the amount of charge transferred when the reaction is
completed.
Since each mole of electron has a charge of 96,485 C (known as the Faraday's constant, F),
q = nF and, ∆G = - nF∆E
At standard conditions, ∆G° = - n F∆E°
The General Nernst Equation
The general Nernst equation correlates the Gibb's Free Energy ∆G and the EMF of a chemical system known as the galvanic
cell. For the reaction
a A + b B = c C + d D and
[C]c [D]d Q = --------- [A]a [B]b
20. Chemistry
18CYB101J
It has been shown that
∆G = ∆G° + RT ln Q and
∆G = - nF∆E
Therefore
- nF∆E = - nF∆E° + R T ln Q
Where, R – is the gas constant (8.314 J mol-1 K-1), T- temperature (in K), Q- reaction quotient,
and F- Faraday constant (96485 C) respectively.
Thus, we have ∆E = ∆E°-R T/ n F ln [C]c [D]d/ [A]a [B]b
This is known as the Nernst equation.
The equation allows us to calculate the cell potential of any galvanic cell for any concentrations.
Some examples are given in the next section to illustrate its application.
23. Chemistry
18CYB101J
Applications of Nernst equation
• In many situations, accurate determination of an ion concentration by direct measurement of a cell potential is impossible
due to the presence of other ions and a lack of information about activity coefficients.
• In such cases it is often possible to determine the ion indirectly by titration with some other ion. For example, the initial
concentration of an ion such as Fe2+ can be found by titrating with a strong oxidizing agent such as Ce4+. The titration is
carried out in one side of a cell whose other half is a reference electrode:
Pt(s) | Fe2+, Fe3+ || ......................... (1)
Initially the left cell contains only Fe2+. As the titrant is added, the ferrous ion is oxidized to Fe3+ in a reaction that is virtually
complete:
Fe2+ + Ce4+ → Fe3+ + Ce3+ ............ (2)
The cell potential is followed as the Fe2+ is added in small increments. Once the first drop of ceric ion titrant has been added,
the potential of the left cell is controlled by the ratio of oxidized and reduced iron according to the Nernst equation
...................... (3)
which causes the potential to rise as more iron becomes oxidized.
24. Chemistry
18CYB101J
When the equivalence point is reached, the Fe2+ will have
been totally consumed (the large equilibrium constant
ensures that this will be so), and the potential will then be
controlled by the concentration ratio of Ce3+/Ce4+.
The idea is that both species of a redox couple must be
present in sufficient concentrations to poise an electrode
(that is, to control its potential according to the Nernst
equation.)
If one works out the actual cell potentials for various
concentrations of all these species, the resulting titration
curve looks much like the familiar acid-base titration
curve.
The end point is found not by measuring a particular cell
voltage, but by finding what volume of titrant gives the
steepest part of the curve.
Fig. Potentiometric titration graph
25. Chemistry
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Application of Nernst Equation-Redox Reaction
• From the thermodynamic point of view, the redox reactions occurring in electrochemical cells are not
spontaneous since external energy is used to produce these reactions (∆G>0, ∆E<0).
• The Nernst equation is suitable for use in electrochemical cells to determine quantities such as potential,
concentration, number of electrons transferred during the process, as well as the electric charge (q= ∆G/nF)
where according to reaction
Oxidations : Zn -> Zn 2+ + 2e-
Reductions : 2H+ + 2e- -> H2 (gas)
The overall reaction: Zn + 2H+ -> Zn 2+ + H2 (gas)
The cell voltage is the sum of potentials of both half reactions written in their current states
E0 = 0.76V + 0 = 0.76V
26. Chemistry
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Since pH is actually defined in terms of hydrogen ion activity and not its concentration, a hydrogen electrode allows a
direct measure of {H+} and thus of –log {H+}, which is the pH.
Application of Nernst Equation-pH
The potential between a pH glass electrode and a reference electrode is defined by the Nernst equation, which is as
follows for a pH measurement:
E = E0 + 2.3 RT / F * log aH+
E0 is the standard potential at aH+ = 1mol/L.
The factor 2.3 RT/F is summarized as the Nernst potential EN and is identical to the change in potential per pH unit. The
value of EN depends on the absolute temperature T Kelvin. (EN is often referred to as the slope factor):
Temperature EN Value (mV)
0 °C EN = 54.2 mV
25 °C EN = 59.2 mV
50 °C EN = 64.1 mV
Fig. 18: Different sources of potential in a combination electrode
27. Chemistry
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In order to measure E1 and assign a definite pH value to it, all other single potentials E2 - E6 have to be constant.
• A thermodynamic equilibrium of the hydrogen ion
arises at the phase boundary between the
measuring solution and the outer gel layer.
• If the activity of the hydrogen ions is different in
the two phases, a hydrogen ion transport will occur.
This leads to a charge at the phase layer, which
prevents any further H+ transport.
Fig. 19: A model representing the pH potentials at the glass membrane
• A thermodynamic equilibrium of the hydrogen ion arises at the phase boundary between the measuring solution and the
outer gel layer. If the activity of the hydrogen ions is different in the two phases, a hydrogen ion transport will occur. This
leads to a charge at the phase layer, which prevents any further H+ transport.
• This resulting potential is responsible for the different hydrogen ion activities in the solution and in the gel layer:
The number of hydrogen ions in the gel layer is given by the silicic acid skeleton of the glass membrane and can be
considered a constant and independent of the measuring solution.
28. Chemistry
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The potential in the outer gel layer is transmitted to the inside of the glass membrane by the Li+ ions found in the glass
membrane, where another phase boundary potential arises:
The total membrane potential is equal to the difference of the two phase boundary potentials
When H+ activity is identical in the two gel layers (the ideal case) and the H+ activity of the
inner electrolyte is kept constant, the following equation is true:
29. Chemistry
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• A solubility equilibrium exists when a chemical compound in the solid state is in chemical
equilibrium with a solution of that compound.
• The equilibrium is an example of dynamic equilibrium in that some individual molecules migrate between
the solid and solution phases such that the rates of dissolution and precipitation are equal to one another.
When equilibrium is established, the solution is said to be saturated. The concentration of the solute in a
saturated solution is known as the solubility.
• Solubility is temperature dependent. A solution containing a higher concentration of solute than the
solubility is said to be supersaturated. A supersaturated solution may be induced to come to equilibrium by
the addition of a "seed" which may be a tiny crystal of the solute, or a tiny solid particle, which initiates
precipitation.
• There are three main types of solubility equilibria.
1. Simple dissolution.
2. Dissolution with dissociation.
3. Constant is known in this case as a solubility product.
4. Dissolution with reaction.
Solubility equilibria (Ksp)
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H 2 (g) + 1/2 0 2 (g) → H 2O (l)
Δf H° 298 . = - 286 kJ mol-1
Since entropy is a state function, entropy values are additive in the same way as enthalpy values:
Δf S = ∑Vi S i
where Vi are stoichiometric coefficients in the chemical equation for the formation of one mole of the compound from
the elements. We find the following valued for absolute entropies, given in the units
J mol-1 K-1 S° 298 (H 2 ,g) = 131 , S° 298 (O2 ,g) = 205, S° 298 (H 2O,l) = 70
Thus the standard entropy of formation for liquid water, Δf S° 298 will be:
Δf S° 298 = - 131 - 1/2 x 205 + 70 = - 163.5 1 J mol-1 K-1
Gibbs Free Energy:
Δf G° 298 = Δ f H° 298 - TΔf S° 298 = - 286 - 298 x (-163.5/1000) = - 237 kJ mol-1 (Spontaneous)
Gibbs’s Free Energy for Water Formations