MCAT Physical : Batteries

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

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?

Possible Answers:

Correct answer:

Explanation:

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 . Next, we combine the details of the galvanic cell in order to arrive at the appropriate units, and determine the current.

Example Question #2 : Batteries

You are charging your cell phone battery with your cell phone charger. What can you conclude about this process?

Possible Answers:

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 releasing voltage

The cell phone battery is acting as an electrolytic cell because it is releasing voltage

The cell phone battery is acting as a galvanic cell because it is acquiring voltage

Correct answer:

The cell phone battery is acting as an electrolytic cell because it is acquiring voltage

Explanation:

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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