MCAT Physical : Batteries
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Example Question #1 : Batteries
Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
The cell above resulted in a transfer of 0.05mol of electrons. The cell ran for four minutes at a constant voltage. What is the current of the cell?
This problem requires us to use dimensional analysis in order to compare what we know, and arrive at the current of the cell. First, we start by noting that the unit for current is Coulombs per second, or 
Example Question #2 : Batteries
You are charging your cell phone battery with your cell phone charger. What can you conclude about this process?
The cell phone battery is acting as a galvanic cell because it is releasing voltage
The cell phone battery is acting as an electrolytic cell because it is acquiring voltage
The cell phone battery is acting as a galvanic cell because it is acquiring voltage
The cell phone battery is acting as an electrolytic cell because it is releasing voltage
The cell phone battery is acting as an electrolytic cell because it is acquiring voltage
A single battery can act as both a galvanic and an electrolytic cell. When a battery is discharging it is considered to be a galvanic cell because it is undergoing a spontaneous redox reaction and is losing voltage. On the other hand, when a battery is charging, it is acquiring voltage (from the phone charger that is connected to an outlet) and is considered an electrolytic cell.
Recall that electrolytic cells facilitate nonspontaneous reactions and require energy to carry out these unfavorable reactions. Charging a battery is a nonspontaneous process (because the reaction involved is the reverse of the reaction that occurs when the battery is discharging) and requires energy in the form of voltage input.
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