Electrochemistry - MCAT Chemical and Physical Foundations of Biological Systems
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
The student in the passage disassembles the cell, and attempts to rebuild it the next day. He forgets, however, to include 
in the solvent of the half cell on the right side of the diagram. Which of the following is likely to happen?
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
The student in the passage disassembles the cell, and attempts to rebuild it the next day. He forgets, however, to include
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There must be 
pre-existing in the right-side half reaction for the cell to function at all. Without the pre-existing ions, the cell has no electron acceptor dissolved in solution, and no electron transfer can therefore take place. Electron transfer is the fundamental energy-producing process that takes place in a voltaic cell.
There must be
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When a galvanic cell contains two different solutions, a salt bridge is often required. The salt bridge allows the two solutions to remain isolated by providing ionic interactions for both solutions, without severely reducing the potential difference. The salt bridge is commonly composed of a potassium chloride solution.
In what direction would you expect the potassium ions to travel in a galvanic cell?
When a galvanic cell contains two different solutions, a salt bridge is often required. The salt bridge allows the two solutions to remain isolated by providing ionic interactions for both solutions, without severely reducing the potential difference. The salt bridge is commonly composed of a potassium chloride solution.
In what direction would you expect the potassium ions to travel in a galvanic cell?
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Potassium ions (K+) will be positively charged, which means they will travel towards the side of the cell that is more negative. Reduction takes place at the cathode, because electrons flow from the anode to the cathode. Since negative charge accumulates at the cathode, the cations will travel in that direction, while the anions will travel towards the anode.
Potassium ions (K+) will be positively charged, which means they will travel towards the side of the cell that is more negative. Reduction takes place at the cathode, because electrons flow from the anode to the cathode. Since negative charge accumulates at the cathode, the cations will travel in that direction, while the anions will travel towards the anode.
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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?
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?
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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.
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
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You are charging your cell phone battery with your cell phone charger. What can you conclude about this process?
You are charging your cell phone battery with your cell phone charger. What can you conclude about this process?
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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.
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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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
How would the voltaic cell depicted above differ from an electrolytic cell?
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
How would the voltaic cell depicted above differ from an electrolytic cell?
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Electrolytic cells require an input of energy, and are used to plate metals by functionally running a voltaic cell in reverse.
Electrolytic cells require an input of energy, and are used to plate metals by functionally running a voltaic cell in reverse.
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Which of the following is not true of electrolytic cells?
Which of the following is not true of electrolytic cells?
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For electrolytic cells, the cell potential is negative; in contrast, galvanic/voltaic cells have positive cell potentials. Electrolysis reactions can only occur if the total potential is positive. An additional voltage input, such as a battery, is required so that the sum of potentials in the electrolytic cell is greater than zero.
Oxidation always occurs at the anode, regardless of cell type, and electrons always travel toward the site of reduction (the cathode). In a galvanic cell, the cathode is positively charged, naturally drawing the flow of electrons. In an electrolytic cell, the cathode is negatively charged, but still requires the flow of electrons to allow reduction to occur. An induced current from a battery is used to propel these electrons against their natural flow.
For electrolytic cells, the cell potential is negative; in contrast, galvanic/voltaic cells have positive cell potentials. Electrolysis reactions can only occur if the total potential is positive. An additional voltage input, such as a battery, is required so that the sum of potentials in the electrolytic cell is greater than zero.
Oxidation always occurs at the anode, regardless of cell type, and electrons always travel toward the site of reduction (the cathode). In a galvanic cell, the cathode is positively charged, naturally drawing the flow of electrons. In an electrolytic cell, the cathode is negatively charged, but still requires the flow of electrons to allow reduction to occur. An induced current from a battery is used to propel these electrons against their natural flow.
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In an electrolytic cell, oxidation takes place at the .
In an electrolytic cell, oxidation takes place at the .
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Electrolytic cells have a negative electromotive force and require an outside energy source to power a non-spontaneous reaction. Galvanic cells, in contrast, have positive potentials and facilitate spontaneous reactions without the need of a power source.
Regardless of cell type, however, oxidation always takes place at the anode and reduction always takes place at the cathode. The flow of electrons is always from the anode to cathode.
Electrolytic cells have a negative electromotive force and require an outside energy source to power a non-spontaneous reaction. Galvanic cells, in contrast, have positive potentials and facilitate spontaneous reactions without the need of a power source.
Regardless of cell type, however, oxidation always takes place at the anode and reduction always takes place at the cathode. The flow of electrons is always from the anode to cathode.
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Which of the following is true about electrolysis?
I. It only involves reactions with 
II. It requires a voltage source
III. It is an exothermic process
Which of the following is true about electrolysis?
I. It only involves reactions with
II. It requires a voltage source
III. It is an exothermic process
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Electrolysis is a specific type of reaction that occurs in an electrolytic cell. An electrochemical cell contains an anode and a cathode that facilitate a redox reaction. In an electrolytic cell (a type of electrochemical cell) the redox reaction that is carried out is a nonspontaneous reaction. Recall that the change in Gibbs free energy for a nonspontaneous, or unfavorable, reaction is always positive; therefore, for electrolysis in an electrolytic cell, the redox reaction has a 
. Statement I is false.
Nonspontaneous reactions are reactions that are unfavorable. This means that energy is required to carry out the reaction. In an electrolytic cell, energy is provided in the form of voltage input. The voltage provided pushes the reaction in the unfavorable direction; therefore, electrolysis reactions require a voltage source. Statement II is true.
Since it requires energy, an electrolysis reaction is considered to be an endothermic process. Recall that endothermic processes are reactions that take in (or require) energy, whereas exothermic processes are reactions that release energy; therefore, electrolysis is an endothermic process. Statement III is false.
Electrolysis is a specific type of reaction that occurs in an electrolytic cell. An electrochemical cell contains an anode and a cathode that facilitate a redox reaction. In an electrolytic cell (a type of electrochemical cell) the redox reaction that is carried out is a nonspontaneous reaction. Recall that the change in Gibbs free energy for a nonspontaneous, or unfavorable, reaction is always positive; therefore, for electrolysis in an electrolytic cell, the redox reaction has a
Nonspontaneous reactions are reactions that are unfavorable. This means that energy is required to carry out the reaction. In an electrolytic cell, energy is provided in the form of voltage input. The voltage provided pushes the reaction in the unfavorable direction; therefore, electrolysis reactions require a voltage source. Statement II is true.
Since it requires energy, an electrolysis reaction is considered to be an endothermic process. Recall that endothermic processes are reactions that take in (or require) energy, whereas exothermic processes are reactions that release energy; therefore, electrolysis is an endothermic process. Statement III is false.
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Consider the following reaction:
How much voltage will you have to apply to carry out this reaction?
Consider the following reaction:
How much voltage will you have to apply to carry out this reaction?
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The question states that the reaction has a negative 
; therefore, the reaction is nonspontaneous. Nonspontaneous reactions are carried out in electrolytic cells (as opposed to galvanic cells). A reaction usually proceeds in the spontaneous direction; therefore, to carry out nonspontaneous reactions you must put energy into the system. Without energy, the reaction shown will occur in the reverse direction.
In an electrolytic cell, energy is provided by an external voltage source. Without energy, the electrolytic cell will have a voltage of 
and the spontaneous (reverse) reaction will occur. For the nonspontaneous reaction to occur, you must attach a voltage source in such a way that the voltage applied is greater than 
and is applied in the opposite direction (nonspontaneous reaction direction). This will force the reaction in the reverse direction and the nonspontaneous reaction will occur; therefore, the external voltage source must provide a voltage greater than 
.
The question states that the reaction has a negative
In an electrolytic cell, energy is provided by an external voltage source. Without energy, the electrolytic cell will have a voltage of
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
If there is a net production of copper ions in the half cell on the left as the reaction proceeds, which of the following must be true?
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
If there is a net production of copper ions in the half cell on the left as the reaction proceeds, which of the following must be true?
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If copper ions are generated as the voltaic cell functions, then the copper is being oxidized, and the silver must be reduced. Reduction and oxidation always occur together in a coupled reaction. This must also mean that the reduction potential for Ag is higher than the reduction potential for Cu.
If copper ions are generated as the voltaic cell functions, then the copper is being oxidized, and the silver must be reduced. Reduction and oxidation always occur together in a coupled reaction. This must also mean that the reduction potential for Ag is higher than the reduction potential for Cu.
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
Instead of silver, a scientist uses a strip of zinc in the opposite half cell from copper. Which of the following is true when comparing this new cell to the cell in the diagram?
The reduction potential of 
is 0.34 volts. The reduction potential for 
is -0.76 volts.
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
Instead of silver, a scientist uses a strip of zinc in the opposite half cell from copper. Which of the following is true when comparing this new cell to the cell in the diagram?
The reduction potential of
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In the new cell, energy can still be produced, but because zinc ions have a lower reduction potential than copper ions, the copper will be reduced and the direction of electron flow will be reversed, as compared to the cell with silver in which copper was oxidized.
In the new cell, energy can still be produced, but because zinc ions have a lower reduction potential than copper ions, the copper will be reduced and the direction of electron flow will be reversed, as compared to the cell with silver in which copper was oxidized.
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
As the difference in the reduction potentials between two half cells increases, what happens to the Gibbs free energy of the reaction?
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
As the difference in the reduction potentials between two half cells increases, what happens to the Gibbs free energy of the reaction?
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The reduction potential of a cell is directly related to the Gibbs free energy by the equation below.
As the reduction potential of a cell becomes more and more positive, the Gibbs free energy value becomes more and more negative.
The reduction potential of a cell is directly related to the Gibbs free energy by the equation below.
As the reduction potential of a cell becomes more and more positive, the Gibbs free energy value becomes more and more negative.
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
In the voltaic cell drawn above, what is true about the species Ag?
The reduction potential for 
is 0.34. The reduction potential for 
0.80.
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
In the voltaic cell drawn above, what is true about the species Ag?
The reduction potential for
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As drawn above, the reaction must involve the oxidation of copper (lower reduction potential) and the reduction of silver (higher reduction potential). Reduction always means that a species gains electrons.
As drawn above, the reaction must involve the oxidation of copper (lower reduction potential) and the reduction of silver (higher reduction potential). Reduction always means that a species gains electrons.
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Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
What is the standard state cell potential for this reaction?
Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
What is the standard state cell potential for this reaction?
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Keep in mind that a galvanic cell will always have a positive voltage, so you can disregard the negative options. The half reactions show the voltage that will result if the element in question is reduced; however, an oxidation-reduction reaction will always have one element oxidized and another element reduced. In the equation shown, solid zinc (Zn) is oxidized, so the voltage of its half reaction is inverted to +0.76V. Next, you add the voltage of iron's reduction, resulting in the overall voltage of the galvanic cell.
Keep in mind that a galvanic cell will always have a positive voltage, so you can disregard the negative options. The half reactions show the voltage that will result if the element in question is reduced; however, an oxidation-reduction reaction will always have one element oxidized and another element reduced. In the equation shown, solid zinc (Zn) is oxidized, so the voltage of its half reaction is inverted to +0.76V. Next, you add the voltage of iron's reduction, resulting in the overall voltage of the galvanic cell.
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Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
Suppose that this galvanic cell was converted into an electrolytic cell. Which of the following statements would be true?
Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
Suppose that this galvanic cell was converted into an electrolytic cell. Which of the following statements would be true?
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An electrolytic cell is best thought of as a cell that requires an external power source in order to work. The reaction will go in the opposite direction of a galvanic cell, meaning that the cell potential will also be inversed and the reaction will be non-spontaneous. As a result, cell potential would be negative in an electrolytic cell.
An electrolytic cell is best thought of as a cell that requires an external power source in order to work. The reaction will go in the opposite direction of a galvanic cell, meaning that the cell potential will also be inversed and the reaction will be non-spontaneous. As a result, cell potential would be negative in an electrolytic cell.
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Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
Assuming standard conditions, what is the free energy for the reaction?
Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
Assuming standard conditions, what is the free energy for the reaction?
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Since the reaction is taking place under standard conditions, we can determine the free energy of the reaction by using the equation
.
n is the number of moles of electrons transferred in the balanced reaction, F is Faraday's constant, and Eo is the cell potential for the reaction.
Since the reaction is taking place under standard conditions, we can determine the free energy of the reaction by using the equation
n is the number of moles of electrons transferred in the balanced reaction, F is Faraday's constant, and Eo is the cell potential for the reaction.
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Determine the cell potential of the following reaction.
Reduction potentials of 
and 
cations are 
and 
, respectively.
Determine the cell potential of the following reaction.
Reduction potentials of
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In the given reaction calcium, 
, is oxidized (loses electrons) and gold, 
, is reduced (gains electrons).
We are only given the reduction potentials. The oxidation potential of 
is the negative of the reduction potential: 
.
Recall that only the moles of electrons must balance for these reactions, therefore no multiplication of the standard potentials is needed when balancing mole atoms; thus the cell potential is the sum of the calcium oxidation potential and the gold reduction potential.
In the given reaction calcium,
We are only given the reduction potentials. The oxidation potential of
Recall that only the moles of electrons must balance for these reactions, therefore no multiplication of the standard potentials is needed when balancing mole atoms; thus the cell potential is the sum of the calcium oxidation potential and the gold reduction potential.
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Consider the following half reactions and corresponding reduction potentials:
Based on the above information, which substance can oxidize 
to 
?
Consider the following half reactions and corresponding reduction potentials:
Based on the above information, which substance can oxidize
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The reduction potential of 
is 
, so the corresponding oxidation potential of 
is 
.
For a substance to oxidize 
to 
, it must have reduction potential greater than 
, so that the sum of the reduction potential of this compounds and the oxidation potential of 
is positive.
The only choice that meets this requirement is 
.
The reduction potential of
For a substance to oxidize
The only choice that meets this requirement is
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A researcher is analyzing an electrolytic cell. In trial 1, he applies 
of current for two hours to the cell and observes that the cathode produces 
of zinc metal. In trial 2, he applies the same amount of current but only for one hour. What will the researcher observe in the cathode during trial 2?
A researcher is analyzing an electrolytic cell. In trial 1, he applies
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Faraday’s Law states that the amount of substance produced in a half-cell is dependent on the charge applied to the system; therefore, the more charge applied the more substance produced. The question states that the researcher applies the same amount of current, but for a shorter time, in trial 2. Recall the definition of current:
This means that charge equals:
Trial 1 and Trial 2 have the same current; however, trial 2 has a smaller time. This means that the charge applied in trial 2 is smaller than the charge applied in trial 1; therefore, according to Faraday’s law, the researcher must observe a smaller mass of zinc metal in trial 2.
Faraday’s Law states that the amount of substance produced in a half-cell is dependent on the charge applied to the system; therefore, the more charge applied the more substance produced. The question states that the researcher applies the same amount of current, but for a shorter time, in trial 2. Recall the definition of current:
This means that charge equals:
Trial 1 and Trial 2 have the same current; however, trial 2 has a smaller time. This means that the charge applied in trial 2 is smaller than the charge applied in trial 1; therefore, according to Faraday’s law, the researcher must observe a smaller mass of zinc metal in trial 2.
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Faraday’s Law states that the amount of product in a cell as the increases.
Faraday’s Law states that the amount of product in a cell as the increases.
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Faraday’s Law states that the amount of product in a half cell is proportional to the charge applied to the cell; therefore, the amount of product in a cell increases as the charge increases. Faraday’s Law states nothing about the relationship between the amount of product and time.
Faraday’s Law states that the amount of product in a half cell is proportional to the charge applied to the cell; therefore, the amount of product in a cell increases as the charge increases. Faraday’s Law states nothing about the relationship between the amount of product and time.
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