MCAT Physical : Physical Chemistry
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Example Question #4 : Oxidation Reduction In Electrochemistry
Consider the reaction below:
Which of the following is true about this reaction?
The half-cell locations cannot be determined without knowing the electrochemical cell potential of the overall reaction
The sodium half-cell is found at the cathode because sodium is being reduced
The sodium half-cell is found at the anode because sodium is being oxidized
The sodium half-cell is found at the cathode because sodium is being oxidized
The sodium half-cell is found at the cathode because sodium is being reduced
In the reaction, a sodium ion (with a charge of 
To solve this question, we don’t need to know the electrochemical cell potential of the reaction. The electrochemical cell potential signifies whether the reaction is spontaneous (positive cell potential) or nonspontaneous (negative cell potential). A spontaneous reaction will occur in a galvanic cell and a nonspontaneous reaction will occur in an electrolytic cell. Remember that, regardless of the type of electrochemical cell, the reduction half-reaction always occurs at the cathode and the oxidation half-reaction always occurs at the anode; therefore, in both cells, the sodium half-cell will be in the cathode and the copper half-cell will be in the anode.
Example Question #1 : Oxidation Reduction In Electrochemistry
Which of the following is the correct direction of electron flow in an electrochemical cell?
Anode to cathode
Cathode to anode
The electron flow direction depends on the metals involved in the half-reactions
The electron flow direction depends on the type of electrochemical cell
Anode to cathode
Electron flow, especially the electrical energy associated with electron flow, is an important characteristic of an electrochemical cell. In a galvanic cell, electrical energy is harnessed from a spontaneous chemical reaction and is used to drive other unfavorable processes. In an electrolytic cell, electrical energy is supplied by an outside voltage source that is used to drive a nonspontaneous chemical reaction.
Recall that cathodes are the site of reduction and anodes are the site of oxidation. Electrons are used up (reactants) in a reduction reaction and electrons are produced (products) in an oxidation reaction; therefore, anodes produce and have an excess of free electron,s whereas cathodes use and have a deficiency of free electrons. Since there are fewer electrons in the cathode, the electrons in an electrochemical cell will flow from the anode to the cathode.
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