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Need help preparing for the General Chemistry section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Electrolytic Cells within Electrochemistry. Watch this video to get all the MCAT study tips you need to do well on this section of the exam!
The standard cell potential of a redox reaction is the sum of the standard oxidation and reduction potentials of the individual reactions occurring in that system. Looking at the equation ΔG° = -nFE°cell we noted that a redox reaction with a negative cell potential has a positive change in Gibbs free energy and is non-spontaneous. Electrolytic cells are electrochemical cells that contain non-spontaneous redox reactions, which will only proceed when electrical energy is applied to them. This section will cover the three main differences between electrolytic cells and galvanic cells: that electrolytic cells have a negative charge on their cathode but a positive charge on their anode, that electrolytic cells are non-spontaneous, and that electrolytic cells require an external power source.
Design of an Electrochemical Cell
Similar to a galvanic cell, an electrochemical cell is composed of a cathode and anode. The anode is defined as the site of oxidation while the cathode is defined as the site of reduction. However, in an electrolytic cell, because the reaction is nonspontaneous, we attach a battery to the cell circuit to power the non-spontaneous redox reaction. In a galvanic cell, electrons were spontaneously produced at the anode and carried to the cathode. In an electrolytic cell, electrons are pulled from the anode by the battery.
Recall that in a galvanic cell, the movement of salt bridge ions into the cathode and anode solutions made them positive and negative, respectively, facilitating the movement of electrons from the anode to the cathode. The movement of electrons from regions of positive to negative charge is a spontaneous process. In contrast, we know that an electrolytic cell is non-spontaneous and requires battery power. In an electrolytic cell, the anode is positively charged and the cathode is negatively charged, disfavoring the flow of electrons from anode to cathode. The battery is required to force electrons from the positively charged anode to negatively charged cathode.
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