Complimentary 1-hour tutoring consultation Schedule Now

Complimentary 1-hour tutoring consultation
Schedule Now

MCAT Content / Electrochemistry / Batteries 2

Batteries

Topic: Electrochemistry

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.


Practice Questions

Khan Academy

MCAT Official Prep (AAMC)

Physics Question Pack Passage 9 Question 55

Key Points

• 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.


Key Terms

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-standard conditions.

Voltage: An electromotive force or potential difference expressed in volts.



Billing Information
We had trouble validating your card. It's possible your card provider is preventing us from charging the card. Please contact your card provider or customer support.
{{ cardForm.errors.get('number') }}
{{ registerForm.errors.get('zip') }}
{{ registerForm.errors.get('coupon') }}
Tax: {{ taxAmount(selectedPlan) | currency spark.currencySymbol }}

Total Price Including Tax: {{ priceWithTax(selectedPlan) | currency spark.currencySymbol }} / {{ selectedPlan.interval | capitalize }}