SmartBook Assignment Chapter 19: Electrochemistry
Imagine that two half-reactions are each measured relative to a standard hydrogen electrode. The standard reduction potential for half-cell A is found to be 1.0 V, while the standard reduction potential for half-cell B is found to be 1.5 V. What will the standard cell potential be when half-cell A is connected to half-cell B to generate a spontaneous reaction?
+0.5 V
Given the standard potential for the half-reaction Ag+ (aq) + e- → Ag (s); Eo = +0.80 V, calculate the standard reduction potential for the half-reaction 2Ag+ (aq) + 2e- → 2Ag (s).
+0.80 V
Co3+ (aq) + Cu (s) → Co2+ (aq) + Cu+ (aq) Calculate the standard cell potential for the reaction shown above, given the following information: Co3+ (aq) + e- → Co2+ (aq); Eo = 1.82 V Cu+ (aq) + e- → Cu (s); Eo = 0.52 V
+1.30 V
Calculate the standard free-energy change for the reaction shown below. 2Fe2+ (aq) + H2O2 (aq) + 2H+ (aq) → 2H2O (l) + 2Fe3+ (aq) Eocell = 1.00 V, F = 96,500 J/V⋅mol e-
-193 kJ
Given the standard potential for the half-reaction Ca2+ (aq) + 2e- → Ca (s); Eo = -2.87 V, what is the standard potential for the half-reaction 2Ca2+ (aq) + 4e- → 2Ca (s)?
-2.87 V
Ag (s) + Li+ (aq) → Ag+ (aq) + Li (s) Calculate the standard cell potential for the above reaction given the following information: Li+ (aq) + e- → Li (s); Eo = -3.05 V Ag+ (aq) + e- → Ag (s); Eo = 0.80 V
-3.85 V
If the equilibrium constant (K) for a chemical reaction is equal to 1, the standard cell potential for this reaction is equal to _____.
0
If the standard cell potential for a reaction is equal to 0 V, ΔG° is equal to _____ kJ.
0 or zero
A concentration cell is constructed with an overall redox equation of Zn2+ (0.50 M) → Zn2+ (0.15 M). What is the cell potential for this concentration cell at 25∘C?
0.015 V
Identify the number of electrons required to balance the following half-reaction. Also indicate whether these electrons must appear as reactants or products. 2H+ + NO3- → NO2 + H2O
1 e-, reactant
When the half-reactions below are balanced to account for electron transfer, the first reaction should be multiplied by _____, and the second reaction should be multiplied by _____. Equation 1: 2H2O → O2 + 4H+ + 4e- Equation 2: Ni2+ + 2e- → Ni
1, 2
The value of Eocell for the reaction below is 0.03 V. What is the value of the equilibrium constant K at 25oC? Ag+ (aq) + Fe2+ (aq) → Ag (s) + Fe3+ (aq)
3.2
What is the equilibrium constant for the redox reaction below under standard conditions? Cu2+(aq) + 2Li (s) → Cu (s) + 2Li+ (aq)
10^115
When hydrogen atoms are balanced in the following (unbalanced) half-reaction, identify the amount of the substance that must be introduced, and where it will appear in the equation. Assume the reaction occurs in acidic medium. 2ClO3- → Cl2 + 6H2O
12 H+ must be added as a reactant.
Prior to balancing oxygen and hydrogen atoms, identify the missing coefficients in the half-reaction _____ NO2- → _____ NH4+.
1; 1
Identify the missing coefficient to balance Mn in the following half-reaction (do not worry about balancing the oxygen atoms). Mn2O3 → _____ MnO2
2
Identify the number of water molecules needed to balance the following half-reaction. Also indicate whether the water will appear as a reactant or a product. MnO4- → MnO2
2 H2O; product
It is easy to forget to consider the number of electrons that take part in an electrochemical reaction when solving for the product of electrolysis. If 6 moles of electrons are consumed during the reduction of Fe3+ to form Fe (s), how many moles of iron are formed?
2 moles Fe
If 6 moles of electrons are passed in an electrolytic cell to reduce Cr3+ ions to chromium metal, how many moles of Cr are generated?
2 moles of Cr
The reaction shown below occurs in a basic solution. Select all the options that correctly describe the balanced equation obtained after all resulting species are combined and/or canceled correctly. Mn2+ + H2O2 → MnO2 + 2H+
2 moles of H2O appear among the products. 2 moles of OH- appear among the reactants.
When hydrogen and oxygen atoms are balanced in the following half-reaction under acidic conditions, which of the following statements are correct? Select all that apply. TiO2 (s) → Ti (s)
2 moles of H2O appear as a product. 4 moles of H+ appear as a reactant.
When the half-reactions below are balanced to account for electron transfer, the first reaction should be multiplied by _____, and the second reaction should be multiplied by _____. Reaction 1: Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O Reaction 2: S + 3H2O → H2SO3 + 4H+ + 4e-
2, 3
Which of the following electrochemical reactions are spontaneous under standard conditions? Select all that apply.
2Co (s) + 3Cl2 (g) → 2CoCl3 (aq); Ecello = 1.6 V 2Cr (s) + 3Sn4+ (aq) → 2Cr3+ (aq) + 3Sn2+ (aq); Ecello = 0.89 V
What is the spontaneous reaction that occurs when the following half-cells are combined? Zn2+ (aq) + 2 e- → Zn (s); Eo = -0.76 Na+ (aq) + e- → Na (s); Eo = -2.71
2Na (s) + Zn2+ (aq) → 2Na+ (aq) + Zn (s)
When the two half-reactions below are added together (ensuring that the electrons cancel), which of the following is the net reaction? Reaction 1: Cu2+ + 2e- → Cu Reaction 2: Fe → Fe3+ + 3e-
3Cu2+ + 2Fe → 3Cu + 2Fe3+
Select all the options that correctly reflect the result when the two reactions given are added together. Make sure you eliminate species that appear on both sides of the equation. Reaction 1: 2BiO+ + 4H+ + 6e- → 2Bi + 2H2O Reaction 2: 6H2O → 3H2O2 + 6H+ + 6e-
4 moles of H2O appear as a reactant. 2 moles of H+ appear as a product.
The reaction shown below occurs in a basic solution. Select all the options that correctly describe the balanced equation obtained after all resulting species are combined and/or canceled correctly. MnO2 + 4H+ + Zn → Mn2+ + 2H2O + Zn2+
4 moles of OH- appear among the products. 2 moles of H2O appear among the reactants.
How many moles of electrons are transferred in the following electrochemical reaction? 3Mn (s) + 2Au3+ (aq) → 3Mn2+ (aq) + 2Au (s)
6
How many moles of electrons are transferred when the two half-reactions shown below are combined to generate the spontaneous balanced chemical reaction with the lowest possible integer coefficients? Cu2+ (aq) + 2e- → Cu (s); Eo = +0.34 V Cr2O72- (aq) + 14H+ (aq) + 6e- → 2Cr3+ (aq) + 7H2O (l); Eo = +1.33 V
6 moles of e-
The following reaction takes place at 25°C, and has a standard cell potential equal to +0.47 V: Cu2+ (aq) + Pb (s) → Pb2+ (aq) + Cu (s) What is the equilibrium constant for this reaction?
7.9 × 10^15
How does alloying chromium with iron, e,g., in stainless steel, prevent the iron from rusting?
A layer of chromium oxide forms on the surface, protecting the iron.
What should be done in order to protect iron from corrosion using cathodic protection?
A more easily oxidized metal should be electrically connected to the iron.
Which of the following statements about a salt bridge in a galvanic cell are correct? Select all that apply.
A salt bridge typically consists of an inert electrolyte. A salt bridge allows cations and anions to flow from one half-cell to the other.
What is the spontaneous reaction that occurs when the two half-cells shown below are combined? Fe3+ (aq) + e- → Fe2+ (aq); Eo = 0.77 V Ag+ (aq) + e- → Ag (s); Eo = 0.80 V
Ag+ (aq) + Fe2+ (aq) → Ag (s) + Fe3+ (aq)
If we were to solve for the cell potential of the following reaction, which two reactions would we first need to find in a standard reduction table? 2 Ag+ (aq) + Zn (s) → 2 Ag (s) + Zn2+ (aq)
Ag+ (aq) + e- → Ag (s) Zn2+ (aq) + 2 e- → Zn (s)
Select all the options that correctly describe how to assign oxidation numbers for atoms in a given species. Assume in all cases that the element in question is bonded to an element other than itself.
Alkaline earth metals (Group 2A) should always be assigned a +2 oxidation number. Alkali metals (Group 1A) should always be assigned a +1 oxidation number. Fluorine should be always be assigned a -1 oxidation number when bonded to other elements.
Which of the following are examples of cathodic protection? (Select all that apply.)
An aluminum anode is attached to a steel beam to keep it from corroding. A coating of zinc is applied to an iron pipeline to keep it from corroding. A magnesium metal bar is connected to a steel ship hull to keep it from rusting.
Which of the following correctly describe the electrolysis of water? Select all that apply.
An electrolyte such as H2SO4 is required for this reaction. Hydrogen gas is generated at the cathode.
Which of the following conditions must be satisfied in order to assemble a standard hydrogen electrode? Select all that apply.
An inert electrode (such as platinum) should be present. HCl should be present at a concentration of 1 M. Hydrogen gas should be bubbled through the solution at a pressure of 1 atm.
Which of the following options describing the assignment of oxidation numbers is/are NOT correct? Select all that apply.
An oxidation number is a measure of the ability for an atom to draw electrons to itself. The sum of the oxidation numbers of all of the elements in a single chemical species must be equal to zero.
The _____ is the electrode at which the reduction reaction occurs, and the _____ is the electrode at which the oxidation reaction occurs.
Blank 1: cathode Blank 2: anode
Electric charge is measured in units of _____ (C). This charge is equal to the _____ in units of amperes (A) that pass over a period of time measured in _____.
Blank 1: coulombs Blank 2: current or electric current Blank 3: seconds
In a galvanic cell, electrochemical reactions occur at the surface of two _____ that are immersed in a(n) _____ solution.
Blank 1: electrodes Blank 2: electrolyte
The Nernst equation is used to calculate the cell potential under _____ conditions. The cell potential is found to differ from the standard cell potential by a factor proportional to the natural log of the reaction _____ (Q).
Blank 1: nonstandard, non-standard, non standard, or nonstandard-state Blank 2: quotient
The energy produced by a galvanic cell can be calculated as the product of the cell _____ (in volts) multiplied by the total ______ that passes through the cell (in coulombs).
Blank 1: potential Blank 2: charge or electric charge
The measure of energy used in electrochemistry is the cell _____ (Ecell), which is the difference in electrical potential between two electrodes. An alternate name for this energy is the _____ (V) of the cell.
Blank 1: potential Blank 2: voltage, electromotive force, or EMF
A conducting medium consisting of an inert electrolyte that allows ions to flow between half-cells of a galvanic cell is called a(n) _____ _____.
Blank 1: salt Blank 2: bridge
A(n) _____ cell uses a spontaneous reaction to generate electrical energy. In this type of cell, the system does work on the _____.
Blank 1: voltaic or galvanic Blank 2: surroundings
In addition to oxygen, the rusting of iron requires _____ as well as a weak acid.
Blank 1: water or H2O
The cell potential for the standard hydrogen electrode (SHE) is by definition equal to _____ volts. If this half-cell is used as the anode and all of the substances in the cathode are under standard conditions, then the potential of the cell is equal to the standard _____ potential of the cathode.
Blank 1: zero, 0, 0.0, or 0.00 Blank 2: reduction
Which of the following statements correctly describe standard electrode potentials? In what way must half-reactions and/or electrode potentials be manipulated when writing a balanced equation for a redox reaction?
By convention, standard electrode potentials are quoted as reduction potentials. The half-reaction for the anode must be reversed when writing the balanced equation for the overall reaction.
Which of the following will result in the passivation of a metal (i.e., protection of the metal from corrosion)? Select all that apply.
Coat the metal with paint or other nonporous coating. Generate an oxide coating by treating the metal with an oxidizing agent.
Which of the following factors affect the cell potential of an electrochemical cell? Select all that apply.
Composition of the electrodes Temperature Concentration of ions in solution
Complete the following equation correctly using the choices shown below. Electric energy (in J) = _____ ×_____
Coulombs Volts
Which of the following is the proper cell notation for the electrochemical reaction shown below? 2 H+ (1 M, aq) + Cu (s) → Cu2+ (1 M, aq) + H2 (1 atm, g) (The hydrogen half-cell uses a graphite inactive electrode.)
Cu (s) | Cu2+ (1 M) || H+ (1 M) | H2 (1 atm) | graphite
In general, when the concentration of the reactants in an electrochemical reaction is large, and the concentration of products is small, which of the following will be true regarding the relationship between Ecell and Ecello?
Ecell > Ecello
Which of the following statements correctly describe electrolytic cells? Select all that apply.
Electrolytic cells require an external energy source for operation. Electrolytic cells involve nonspontaneous reactions. Electroplating is one example of the use of an electrolytic cell.
CO2 (g) + 4H+ (aq) + 4e- → C (s) + 2H2O (l); Eo = +0.41 V Al3+ (aq) + 3e- → Al (s); Eo = -1.66 V Given the two standard reduction potentials above, calculate the standard cell potential for the following reaction: 4Al3+ (aq) + 3C (s) + 6H2O (l)→ 4Al (s) + 3CO2 (g) + 12H+ (aq)
Eo = -2.07 V
Li+ (aq) + e- → Li (s); Eo = -3.05 V Cl2 (g) + 2e- → 2Cl- (aq); Eo = 1.36 V Given the two standard reduction potentials above, calculate the standard cell potential for the following reaction: 2Li+ (aq) + 2Cl- (aq) → 2Li (s) + Cl2 (g)
Eo = -4.41 V
Which of the following equations could be used to calculate Eocell? Select all that apply. Assume that all electrode potentials are quoted as reduction potentials.
Eo cell = Eo cathode - Eo anode Eo cell = Eo red - Eo ox
Which of the following options correctly describe the ways in which the Faraday constant can be used? Select all that apply.
F allows one to calculate the total charge transferred (in C), given the moles of electrons transferred. F allows the calculation of the energy change (in J) for a reaction, given the moles of electrons transferred and the cell potential.
True or false: When calcium ions (Ca2+) are electrolytically reduced to calcium metal, the number of moles of electrons used will be equal to the number moles of calcium metal produced.
False
Which of the following statements correctly describes why a voltaic cell requires the physical separation of electrochemical half-reactions?
Generating a flow of electrons through a wire requires physical separation.
Which of the following statements correctly describe the reactions occurring in a hydrogen fuel cell? Select all that apply.
H2 (g) is oxidized at the anode. O2 (g) is the reactant at the cathode in the fuel cell.
To which of the following half-reactions must 2 electrons appear as products in order to balance the equation?
H2 + 2OH- → 2H2O H2O + PbO → PbO2 + 2H+
Na+ + e- → Na; Eo = -2.71 V Cl2 + 2e- → 2 Cl-; Eo = +1.36 V 2H2O + 2e- → H2 + 2OH-; Eo = -0.83 V O2 + 4H+ + 4e- → 2H2O; Eo = +1.23 V An aqueous NaCl solution is electrolyzed. What are the products at the cathode and anode?
H2 and OH- form at the cathode; Cl2 forms at the anode.
Which compounds or solutions are in an appropriate state for the measurement of Ecello for the reaction given below? Select all that apply. Cu2+ (aq) + H2 (g) → Cu (s) + 2H+ (aq)
H2 gas at 1 atm 1.0 M Cu2+
For the chemical reaction shown below, which of the following (unbalanced) reactions should be used as the starting point for the reduction half-reaction? 2Na + 2H2O → 2NaOH + H2
H2O → H2
When a redox reaction that takes place in an acidic solution involves an oxygen imbalance, oxygen should be balanced by adding _____ as needed, while hydrogen should be balanced by adding _____.
H2O, H+
Given the two half-cell reactions below, identify the spontaneous reaction that would occur between them. I2 (s) + 2e− → 2I− (ag); E° = +0.53V Mn2+ (ag) + 2e− → Mn (s); E° = −1.18V
I2 (s) + Mn (s) → 2I− (ag) + Mn2+ (ag)
In which of the following (unbalanced) half-reactions will 1 mole of water appear as a reactant when oxygen atoms are balanced? Select all that apply.
N2O5 → 2NO3 Na → NaOH
Na+ + e- → Na; Eo = -2.7 V Cl2 + 2 e- → 2 Cl-; Eo = 1.4 V Consider the reactions occurring in an electrolytic cell at two inactive electrodes immersed in anhydrous molten sodium chloride. Which products form at the cathode and anode?
Na forms at the cathode; Cl2 forms at the anode.
Given the two half-reactions below, which reaction represents reduction when a spontaneous process occurs? Cr3+ + 3e- → Cr; Eo = -0.74 Ni2+ + 2e- → Ni; Eo = -0.28
Ni2+ + 2e- → Ni
Which of the following must be balanced in order to balance a redox reaction? Select all that apply.
Number of atoms of each type Overall charge
Which of the following options describe the additional step(s) required to balance a redox reaction that takes place in a basic solution (as opposed to an acidic solution)? Select all that apply.
OH- must be added to each side of the equation in order to react with H+. Each OH- ion added will combine with one H+ that is on the same side of the equation to form H2O.
Which factor below does NOT directly affect the cell potential of a galvanic cell?
Size of the cell
Which half-cell is used as the standard reference for all other half-cell potentials?
Standard hydrogen electrode
Which of the following statements correctly describe standard reduction potentials? Select all that apply.
The amount of electrolyte solution/electrode material present has no effect on the standard reduction potential. Standard cell potential is an intensive property.
Select all the options that correctly describe the shorthand notation used to represent an electrochemical cell.
The anode is written first, on the left side of the cell notation. Concentrations of electrolyte solutions are shown in parentheses next to the formula of the ion in solution. A single vertical line in cell notation represents a phase boundary.
Which of the following best explains why the following chemical reaction is not balanced? Cu2+ (aq) + Fe (s) → Cu (s) + Fe3+ (aq)
The charge is not balanced.
Which of the following features make a lithium-ion battery more advantageous than other battery types?
The lithium-ion battery can be recharged hundreds of times. The cell potential for a lithium-ion battery is large. A relatively small amount of lithium metal is required to produce a mole of electrons.
When zinc metal is immersed in a 1.0 M solution of copper (II) chloride at 25oC, no electrochemical work may be extracted, even though a spontaneous reaction occurs. What is wrong with this cell design?
The oxidation and reduction reactions must be physically separated.
Select all the options that correctly describe the redox reaction shown. H2 (g) + Cl2 (g) → 2HCl (g)
The oxidation number of Cl changes from 0 to -1. The oxidation number of H changes from 0 to +1.
Which of the following is correct regarding fuel cells?
The simplest type of fuel cell consists of an electrolyte solution and two inert electrodes.
A galvanic cell is generated by combining a Cu/CuSO4 half-cell with another Cu/CuSO4 half-cell. The measured cell potential is not zero. What is the most likely explanation for this behavior?
The two electrodes must contain different concentrations of CuSO4.
When water is hydrolyzed in the presence of NaCl, the possible half-cell equations are: Cathode: 2 H2O (l) + 2e- → H2 (g) + 2 OH- (aq); Eo = -0.83 V Na+ (aq) + e- → Na (s); Eo = -2.71 V Anode: 2 Cl- (aq) → Cl2 (g) + 2e-; Eo = -1.36 V 2H2O (l) → O2 (g) + 4H+ (aq) + 4e-; Eo = -1.23 V Experimentally, it is found that H2 (g) and Cl2 (g) are formed. What is the best explanation for this?
There is a significant overvoltage associated with the oxidation of water to form oxygen.
True or false: It is possible for an electrochemical cell composed of the same reaction in both half cells (such as the one shown below) to have a nonzero cell potential. Zn2+ (aq) + Zn (s) → Zn (s) + Zn2+ (aq)
True
True or false: The overvoltage is the difference between the calculated voltage for an electrolytic cell and the actual voltage required for electrolysis.
True
Which of the following are required for corrosion of iron to occur? Select all that apply.
Water Acid Oxygen
Given the standard reduction potentials below, will barium metal react with aqueous magnesium ions spontaneously under standard conditions? Why? Select the best answer among the choices below. Mg2+ (aq) + 2e- → Mg (s); Eo = -2.37 V Ba2+ (aq) + 2e- → Ba (s); Eo = -2.90 V
Yes, because the standard cell potential is positive.
Which of the following options correctly describe the most common dry cell battery? Select all that apply.
Zn is the anode in this cell. MnO2 is a component of the battery.
Based on the following reaction, identify ALL the species that should be included in the oxidation half-reaction equation. Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)
Zn2+ (aq) Zn (s)
Use the Nernst equation to solve for the concentration of Ag+ in unknown solution, if, when a silver electrode is immersed into it at 25.0°C, and it is tested against a 1.0 M AgNO3/Ag electrode, a 0.250-V cell potential develops. The overall reaction is given by Ag+ (1.0 M) + Ag (s) → Ag (s) + Ag+ (x M)
[Ag+] = 6.03 × 10^-5 M
A redox reaction is a chemical reaction that involves _____.
a transfer of electrons from one reactant to another
In a lithium-ion battery, lithium ions migrate from the _____ to the _____ in order to balance the total charge as electrons pass through the external circuit.
anode; cathode
The electrode at which the oxidation reaction occurs is called the _____, while the electrode at which the reduction reaction occurs is called the _____.
anode; cathode
If one were to construct an electrochemical cell consisting of two Zn2+/Zn electrodes at two different concentrations, the more concentrated cell will be the _____.
cathode
An electrochemical cell that is constructed using the same electrode in both half-cells with different concentrations of electrolyte in each is called a(n) _____ cell.
concentration
The SI unit of current is the ampere, which is defined as the flow of charge in units of _____ over a period of time measured in _____.
coulombs; seconds
Alkaline batteries adopted their name from the _____ that is present in the reactions at both the zinc anode and the MnO2 cathode.
hydroxide ion
A property that remains the same when the amount of substance changes is known as an ______ property.
intensive
A battery consisting of an anode and cathode made of lead oxide and immersed in an aqueous solution of sulfuric acid is known as a _____ battery.
lead-acid, lead acid, lead, lead storage, or Pb
Oxidation involves the _____ of electrons, while reduction involves the _____ of electrons.
loss; gain
The Faraday constant F allows one to calculate the number of _____ of electrons, given the total charge in coulombs.
moles or mol
If due to a change in reaction conditions the standard cell potential of an electrochemical reaction becomes more negative, the standard free-energy change will become ______, and the equilibrium constant will become ______.
more positive, smaller
In addition to the standard cell potential, which information below is required to solve for the nonstandard cell potential for an electrochemical reaction using the Nernst equation?
n, the number of electrons in the balanced reaction Q, the reaction quotient
In some electrolysis reactions, e.g., the electrolysis of aqueous NaCl, the products are different from those predicted by tabulated reduction potentials. This may be due to a(n) ______ associated with one of the possible half-reactions.
overvoltage
The difference between the calculated voltage (based on standard potentials) and the actual voltage required to cause electrolysis is called _____.
overvoltage or overpotential
When predicting the spontaneous reaction between two different half-cells, the reaction with the most negative reduction potential will be the _____ reaction, while the reaction with the most positive reduction potential will be the _____ reaction.
oxidation, reduction
A voltaic cell will always have a _____ cell potential during operation, while an electrolytic cell will have a _____ cell potential.
positive; negative
When E°cell is positive, ______ are favored and the equilibrium constant K is ______ than 1.
products; greater
The _____ cell potential (Ecello) is measured with gases at a pressure of 1 atm, solutions at 1 M, and solids or liquids in their pure states.
standard