A battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices.
The Nernst equation can be used to determine the total voltage, or electromotive force, for a full electrochemical cell. The Nernst Equation enables the determination of cell potential under non-standard conditions. The equation relates the electromotive force (emf) of a nonstandard cell to the standard electrode potential, temperature, and activities (often approximated by concentrations) of the chemical species undergoing reduction and oxidation. The equation can be simplified as:
In this equation:
– E is the electromotive force of the non-standard cell
– Eo is the electromotive force of the standard cell
– n is the number of moles of electrons transferred in the reaction
where the uppercase letters are concentrations, and the lowercase letters are stoichiometric coefficients for the overall redox reaction: aA + bB → cC + dD
Electromotive force (emf) is the potential difference of a source, or a battery, when no current is flowing. Terminal voltage is the voltage output of a device measured across its terminals.
A lead storage battery, also known as a lead-acid provides high currents and stores charge for long periods of time, making them essential for vehicles. A lead storage battery is the oldest type of rechargeable battery and one of the most common energy storage devices.
Although the batteries are reliable, they have a limited life, are heavy to ship, and contain toxic materials that require specific removal methods at the end of their useful life. Lead-acid batteries have moderate power density and good response time. Depending on the power conversion technology incorporated, batteries can go from accepting energy to supplying energy instantaneously. Lead-acid batteries are affected by temperature and must be maintained in order to achieve maximum life expectancy.
Nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries, lithium-ion (Li-ion) batteries, and lithium-ion polymer (LiPo) batteries are a few commonly used rechargeable batteries. As with all batteries, rechargeable batteries consist of an anode, a cathode, and an electrolyte. During charging, the anode material is oxidized and produces while the cathode is reduced and consumes electrons.
MCAT Official Prep (AAMC)
Physics Question Pack Passage 9 Question 55
• When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode.
• The Nernst equation can be used to determine the total voltage, or electromotive force, for a full electrochemical cell (a battery).
• Lead-acid batteries are reliable sources which provide high currents. However, they have a limited life, are heavy to ship, and contain toxic materials.
• Nickel-cadmium batteries are commonly used as rechargeable batteries. During charging, the anode material is oxidized, producing electrons, and the cathode is reduced, consuming electrons.
Electromotive force (emf): is the potential difference of a source when no current is flowing in a circuit.
Electrochemical or Voltaic cell: A cell, such as in a battery, in which an irreversible chemical reaction generates electricity; a cell that cannot be recharged.
Electrolyte: a substance containing free ions that carry electric current.
Anode: The electrode of an electrochemical cell at which oxidation (loss of electrons) occurs.
Cathode: The electrode of an electrochemical cell at which reduction (gain of electrons) occurs.
Nernst Equation: Enables the determination of cell potential under non-
Voltage: An electromotive force or potential difference expressed in volts.