Need help preparing for the General Chemistry section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Standard Reduction/Oxidation Potential and Cell Potential of Electrochemistry. Watch this video to get all the MCAT study tips you need to do well on this section of the exam!
Halogens, such as fluorine and bromine, are exceptionally reactive elements. They want to gain a single electron to fill up their valence shell. We can describe the tendency of a compound to gain electrons by a value of standard reduction potential (Eo).
Standard Reduction Potential
Standard reduction potential is a measure of how much a species intrinsically wants to be reduced. Some chemical species want to be reduced, some want to be oxidized, and some do not have a preference for either. We express this desire with a value of standard reduction potential, which has units of volts. If you are asked to do a calculation with standard reduction potentials, a table such as the one below would be provided. Note that since chlorine has the most positive reduction potential, it has the greatest desire to gain electrons. Free hydrogen has no desire to gain electrons, while sodium ion has the least desire to gain electrons. Note that the value of standard reduction potential does not change with the quantity of substance. If you had 10 moles of chlorine, they would have the same reduction potential as 1 mole of chlorine.
Standard Oxidation Potential
Standard oxidation potential is the opposite of standard reduction potential. Instead of measuring how much a species wants to be reduced, it measures how much a species wants to be oxidized. To find the standard oxidation potential, simply multiple the standard reduction potential of an atom by negative 1. The oxidation potentials for the 5 reactions we already went over are shown below. In this table, we can see that sodium has the greatest desire to be oxidized, whereas chlorine has the least desire to be oxidized.
Standard Cell Potential
A redox reaction is composed of a reduction reaction and oxidation reaction. To determine how favorable a redox reaction is, we need to consider the reduction potential and oxidation potential of each individual reaction and sum them. The sum of the standard potentials for the individual reduction and oxidation reactions is the standard cell potential (Eocell) of a redox reaction.
The more positive a value of cell potential is, the more the redox reaction favors oxidation, whereas a more negative values shows that the redox reaction favors reduction. Recall from our video on redox reactions that oxidation reactions are associated with a release in energy, which is why they are used to produce energy by our cells. A reaction that releases energy is exergonic, which we know to be spontaneous. Correspondingly, there is an equation that relates standard cell potential to standard Gibbs free energy, which helps us quantitatively understand why a positive cell potential implies a spontaneous redox reaction.
In the equation above, ΔG° is the change in standard Gibbs free energy, F is Faraday’s constant (96,500 Coulombs/mole of electrons), and n is the number of moles of electrons transferred between compounds in the redox reaction. To find the n of a redox reaction, simply determine how many electrons were oxidized from the reductant and given to the oxidant. Note that a reaction is spontaneous when its change in G is negative, and nonspontaneous when its change in G is positive. Based on this equation, we can see that a redox reaction with a positive standard cell potential must have a negative Gibbs free energy. Therefore, oxidation reactions are spontaneous. In future videos, we will visit biological systems such as the electron transport chain, which is a system composed of redox reactions.
MEDSCHOOLCOACH
To watch more MCAT video tutorials like this and have access to study scheduling, progress tracking, flashcard and question bank, download MCAT Prep by MedSchoolCoach
IOS Link: play.google.com/store/apps/de...
Apple Link: apps.apple.com/us/app/mcat-pr...
#medschoolcoach #MCATprep #MCATstudytools