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Chapter 20: Problem 31

(a) What is the definition of the volt? (b) Do all voltaic cells produce a positive cell potential?

Short Answer

Expert verified
(a) A volt is the potential difference when one joule of energy moves one coulomb of charge. (b) Not all voltaic cells have positive cell potentials; only properly designed ones do.

Step by step solution

01

Understanding the Definition of Volt

The definition of a volt can be found by understanding how electrical potential energy is measured. One volt is defined as the potential difference between two points in an electric circuit where one joule of energy is used to move one coulomb of charge between those points. Therefore, \[ 1 \text{ Volt} = \frac{1 \text{ Joule}}{1 \text{ Coulomb}}. \]
02

Definition of Voltaic Cells and Cell Potential

Voltaic cells convert chemical energy into electrical energy and provide the electromotive force or cell potential to drive an electric current through an external circuit. The cell potential is calculated using the standard reduction potentials of the electrodes involved in the reaction.
03

Analyzing Cell Potentials in Voltaic Cells

Not all voltaic cells produce a positive cell potential. The cell potential depends on the difference in reduction potentials of the anode and cathode. A voltaic cell will only operate spontaneously with a positive cell potential, meaning it favors the forward reaction. If constructed improperly with the wrong electrodes, a cell may have a negative cell potential and not function spontaneously.
04

Determining Conditions for Positive Cell Potential

To ensure a positive cell potential, the electrode with a higher reduction potential should act as the cathode, and the one with the lower reduction potential should be the anode. The equation \[ E_{\text{cell}} = E_{\text{cathode}} - E_{\text{anode}} \] shows that the standard cell potential is positive when the cathode's reduction potential exceeds the anode's.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Defining Voltage
Understanding the definition of voltage is crucial when studying electrical circuits. Voltage, also known as electric potential difference, is like the pressure pushing electrical charges through a conductor. In scientific terms, one volt is the potential difference between two points that will move one coulomb of charge with one joule of energy. Think of it as the energy "cost" of moving charge between points.
  • Voltage = Energy per charge, measured as 1 Volt = 1 Joule per 1 Coulomb.
  • It鈥檚 fundamental for understanding how electrical systems distribute energy.
In practical terms, when you connect a battery to a circuit, the voltage is the force that drives the electric current from the battery through the circuit.
Understanding Cell Potential
Cell potential, also referred to as the electromotive force (EMF) of a cell, is a key concept in electrochemistry, specifically in the context of voltaic cells. Voltaic cells, such as batteries, convert chemical energy into electrical energy. They function by having two different electrodes in contact with an electrolyte.
  • Cell potential indicates the force driving electrons to move through an external circuit.
  • It鈥檚 determined by measuring the voltage across the two electrodes when the circuit is open.
The difference in reduction potentials between the cathode and anode dictates the magnitude of the cell potential. A higher cell potential means a greater ability to produce electrical current.
Exploring Electromotive Force (EMF)
The term electromotive force (EMF) might sound like it involves mechanical motion, but instead, it is all about electricity. EMF is essentially the voltage generated by a voltaic cell or battery when no current is drawn from it鈥攖hink of it as the cell鈥檚 maximum potential.
  • EMF is crucial since it helps predict the cell鈥檚 performance and efficiency.
  • Although named 'force,' it is measured in volts, not newtons.
Whenever a voltaic cell is used, the EMF indicates how much energy per charge is available to move through the circuit, driving the electrical current.
Standard Reduction Potentials
Standard reduction potentials are essential for determining how much voltage a voltaic cell can produce. They provide a reference point to predict the cell potential of various electrochemical cells. Each element has a specific electrode potential, which when used in a cell, can help calculate the overall cell potential.
  • Standard reduction potentials are measured under standard conditions (25掳C, 1 M concentration, 1 atm pressure).
  • Electrodes with higher reduction potentials serve as cathodes, while those with lower potentials act as anodes.
To calculate the cell potential, use the standard reduction potentials of the cathode and anode with the equation: \[ E_{\text{cell}} = E_{\text{cathode}} - E_{\text{anode}} \]This equation helps ensure that a voltaic cell operates efficiently, with a positive cell potential indicating that the cell will work spontaneously.

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Most popular questions from this chapter

(a) What is meant by the term reduction? (b) On which side of a reduction half-reaction do the electrons appear? (c) What is meant by the term reductant? (d) What is meant by the term reducing agent?

If the equilibrium constant for a two-electron redox reaction at \(298 \mathrm{~K}\) is \(2.2 \times 10^{5}\), calculate the corresponding \(\Delta G^{\circ}\) and \(E^{\circ}\).

Indicate whether each of the following statements is true or false: (a) If something is reduced, it is formally losing electrons. (b) A reducing agent gets oxidized as it reacts. (c) An oxidizing agent is needed to convert \(\mathrm{CO}\) into \(\mathrm{CO}_{2}\).

(a) Suppose that an alkaline battery was manufactured using cadmium metal rather than zinc. What effect would this have on the cell emf? (b) What environmental advantage is provided by the use of nickel-metal hydride batteries over nickel-cadmium batteries?

Iron corrodes to produce rust, \(\mathrm{Fe}_{2} \mathrm{O}_{3},\) but other corrosion products that can form are Fe(O)(OH), iron oxyhydroxide, and magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4} \cdot(\mathbf{a})\) What is the oxidation number of Fe in iron oxyhydroxide, assuming oxygen's oxidation number is \(-2 ?\) (b) The oxidation number for Fe in magnetite was controversial for a long time. If we assume that oxygen's oxidation number is -2 , and Fe has a unique oxidation number, what is the oxidation number for Fe in magnetite? (c) It turns out that there are two different kinds of Fe in magnetite that have different oxidation numbers. Suggest what these oxidation numbers are and what their relative stoichiometry must be, assuming oxygen's oxidation number is -2 .
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