cell of emf

Introduction

The concept of electromotive force (EMF) in a cell, also known as electrochemical cell potential, is crucial in understanding how electrochemical cells generate electrical energy.The discovery of EMF can be traced back to Alessandro Volta, an Italian scientist. He created the first chemical battery, known as the Voltaic Pile, in 1800. This device was made from alternating layers of zinc and copper discs, separated by layers of paper soaked in saltwater. The Voltaic Pile was the first device to provide a steady and continuous electric current, and it demonstrated the concept of EMF by producing a voltage. Carnot, a French physicist, Nicolas Leonard Sadi carnot in 1824 contributed to the theoretical understanding of energy transformations, including the principles that would later relate to electrochemical cells and their efficiency. Faraday's work on electrolysis and his laws of electrolysis were crucial for understanding the behavior of cells. His research established a quantitative relationship between the amount of substance transformed during electrolysis and the amount of electrical charge passed through the cell, helping to link EMF with chemical reactions. In 1836 the Daniell cell, developed by British chemist John Daniell, was one of the first practical and reliable electrochemical cells. It used a copper sulfate solution and a zinc sulfate solution with copper and zinc electrodes, respectively. The Daniell cell provided a more consistent and higher EMF compared to earlier cells.

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This Story also Contains

1. Introduction
2. Some Solved Examples
3. Summary

EMF is the voltage developed by any source of electrical energy such as a battery or cell. It represents the potential difference generated between two electrodes in a cell when no current is flowing. The EMF of a cell is measured when no current is flowing through the cell (i.e., in an open circuit). It can be thought of as the maximum potential difference that the cell can deliver. The EMF of a cell can be calculated using the Nernst equation, which relates the cell potential to the concentrations of the reactants and products in the cell's electrochemical reaction. Modern research continues to explore ways to improve the efficiency and capacity of electrochemical cells, including advancements in battery technology and the development of new types of cells with higher EMF and longer life. Understanding EMF is crucial for designing and operating batteries, fuel cells, and other electrochemical devices. It plays a significant role in fields ranging from portable electronics to renewable energy storage systems.

EMF of cell

It is the potential difference between the two terminals of the cell when no current is drawn from it. It is measured with the help of potentiometer or vacuum tube voltmeter.

Calculation of the EMF of the Cell
Mathematically, it may be expressed as
Ecell or EMF=[Ered ( cathode )−Ered ( anode )]Eelll ∘ or EMF∘=[Ered ∘( cathode )−Ered ∘( anode )]

• Characteristics of cell and cell potential.
• For cell reaction to occur the E_cell should be positive. This can happen only if E_red (cathode) > E_red(anode).
• E^o cell must be positive for a spontaneous reaction.
• It measures free energy change for maximum convertibility of heat into useful work.
• It causes the flow of current from the electrode of the higher E^o value to the lower E^o value.

Difference between EMF and Cell Potential

EMF Cell Potential

It is measured by the potentiometer.

It is measured by a voltmeter.

It is the potential difference between two electrodes when no current is flowing in the circuit.

It is the potential difference between two electrodes when a current is flowing through the circuit.

It is the maximum voltage obtained from the cell.

It is less than the maximum voltage.

It corresponds to the maximum useful work obtained from the galvanic cells.

It does not correspond to maintaining useful work obtained from Galvanic Cell

For a better understanding of the topic and to learn more about EMF of cell l with video lesson we provide the link to the

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Some Solved Examples

EXAMPLE.1

1. Which of the following equations connects electrode potential to reaction quotient?

1)Kohlrausch's equation

2) (correct)Nernst equation

3) Ohm's equation

4)Faraday equation

Solution

As we have learned,

Electrode Potential and EMF of Cells -

It is the potential difference between the two terminals of the cell when no current is drawn from it. It is measured with the help of potentiometer or vacuum tube voltmeter.
Nernst equation

E=E⁰−RTnFln⁡Q

Where E= electrode potential and Q = reaction quotient

Hence, the answer is the option (2).

EXAMPLE.2

2. If zinc is kept in CuSO₄ solution, copper gets precipitated because the electrode potential of zinc is

1)copper

2) (correct) copper

3)sulphate

4)none

Solution

Ezinc 0=−0.76,Ecopper 0=+0.34

The standard electrode potential of zinc < copper and hence Zinc copper from its salt.

Hence, the answer is the option (2).

EXAMPLE.3

3. Arrange the following in the order of their decreasing electrode oxidizing potential Mg, K, Ba, Ca

1)Ba, Ca, K, Mg

2) (correct)K, Ba, Ca, Mg

3)Ca, Mg, K, Ba

4)Mg, Ca, Ba, K

Solution

As we have learned,

The correct order can be obtained from the electrochemical series.

Hence, the answer is the option (2).

EXAMPLE.4

4. EMF of a cell in terms of the reduction potential of its left and right electrodes is

1)E=Eleft −Eright

2)E=Eleft +Eright

3) (correct)E=Eright −Eleft

4)E=−(Eright +Eleft )

Solution

As we learned from the concept

We know that E cell = Reduction potential of Cathode + Oxidation potential of Anode

= Reduction potential of Cathode - Reduction potential of Anode

= E_right - E_left

Hence, the answer is the option (3).

EXAMPLE.5

5. If ϕ denotes reduction potential, then which is true?

1) (correct)Ecell=ϕright −ϕleft

2)Ecell ∘=ϕleft +ϕright

3)Ecell ∘=ϕleft −ϕright

4)Ecell ∘=−(ϕleft +ϕright )

Solution

_{Ecell o} = reduction potential (cathode, right) + Oxidation potential (anode, left)

_Ecell∘ = Reduction Potential (right) - Reduction potential (left)

If ϕ is reduction potential, then

_Ecell∘ = ∅right −∅left

Hence, the answer is the option (1).

EXAMPLE.6

6. The standard electrode potentials(EM+∣M0) of four metals A, B, C, and D are - 1.2 V, 0.6 V, 0.85 V, and - 0.76 V, respectively. The sequence of deposition of metals on applying potential is :

1) A, C, B, D

2) B, D, C, A

3) (correct)C, B, D, A

4)D, A, B, C

Solution

The higher the standard electrode potentialEM+∣M0 of the metal, the greater its tendency to get reduced and deposited on the electrode.

Order of the given E₀ value : 0.85 V>0.6 V>−0.76 V>−1.2

The order of deposition will be C, B, D, and A.

Hence, the answer is the option (3).

Summary

EMF of a cell is a fundamental parameter that influences the efficiency, performance, and usability of a wide range of technologies, from everyday consumer electronics to advanced energy storage solutions. The EMF of a battery determines the voltage it can provide to power electronic devices. High EMF batteries, like lithium-ion batteries, are used in smartphones, laptops, and tablets due to their ability to deliver a stable and high voltage while being compact and lightweight. Rechargeable batteries, such as NiMH and Li-ion, rely on their EMF to provide consistent power over many charge-discharge cycles. This is essential for devices that require frequent recharging and sustained performance. In renewable energy systems like solar and wind power, batteries store excess energy generated when production exceeds immediate demand. The EMF of these batteries affects their efficiency and capacity. High EMF cells can store more energy and provide a more stable supply. Large-scale energy storage systems use batteries with high EMF to balance supply and demand on the electrical grid. These systems help stabilize the grid by storing excess energy during peak production times and releasing it during high demand. Electronic vehicle EVs use batteries with high EMF to power electric motors. The EMF determines the vehicle’s range and performance. Advances in battery technology aim to increase EMF and energy density, allowing for longer driving ranges and faster charging times. Batteries with consistent EMF are crucial for telecommunications equipment to maintain reliable signal transmission. Variations in EMF can affect signal strength and quality. Batteries with high EMF can often deliver power over a longer period, reducing the frequency of recharging or replacement. For electric vehicles and high-performance devices, high EMF translates to better performance, including faster speeds, longer ranges, and more powerful operations. Consistent EMF is critical for maintaining stable performance in both consumer electronics and industrial applications. It ensures that devices operate reliably without interruptions.