Chapter 7

What energy change is associated with the reaction to obtain one mole of H2 from one mole of water vapor? The balanced equation is 2 H2O(g) -> 2H2(g) + O2(g) and the relevant bond energies are: H — H = 436 kJ/mol; H — O = 467 kJ/mol; O — O = 146 kJ/mol; O O = 498 kJ/mol.

A. -249 kJ B. +249 kJ C. -436 kJ D. +436 kJ Feedback: Write a balanced equation and then take the energy of the bonds formed minus the bonds broken. B

Which is an oxidation half-reaction?

A. 2 H2 + O2-> 2 H2O B. Zn ->Zn2+ + 2 e¯ C. 2 HCl + Ba(OH)2-> 2 H2O + BaCl2 D. Cl2 + 2 e¯ -> 2 Cl¯ Feedback: Loss of electrons is oxidation. B

For the compound FeCl3, what is the oxidation state of Fe?

A. 2+ B. 3+ C. 4+ D. Mixture between 2+ and 3+ B

For the compound Fe3O4, what is the oxidation state of Fe?

A. 2+ B. 3+ C. 4+ D. Mixture between 2+ and 3+ D

Why can the lead-acid batteries used in cars generate electricity for several years before running down?

A. A lead-acid battery is so large that it holds large quantities of the chemicals whose electrochemical interaction creates the electricity B. The mechanical motion of the engine drives an alternator that generates electricity to recharge the battery C. These batteries are used only to generate the electricity that makes the first spark plug "spark." Therefore, they are hardly used at all when a car is started, and never when it is driven D. The electrons they generate, not the chemical components, provide almost all of the electricity Feedback: Think about how quickly a car will stop running if the alternator goes out. B

Which is not a component of a fuel cell?

A. A timer B. An anode C. A cathode D. An electrolyte Feedback: Remember that this is just like a battery except that fuel flows into the cell continuously. A

Which type of battery is widely used to store the excess energy generated by windmill farms and solar panels?

A. Alkaline B. Lithium ion C. Lead acid D. Nickel-metal hydride Feedback: Think about which is cheaper and readily rechargeable. C

Which type of battery is best for use in heart (cardiac) pacemakers?

A. Alkaline B. Lithium-iodine C. Mercury D. Nickel-cadmium Feedback: Think about which has long life and little toxicity. B

Why doesn't water naturally become hydrogen and oxygen gas when exposed to light?

A. There isn't enough energy in the light. B. Thermal energy is the only appropriate type of energy to split water. C. You must use electrons to split water. D. Water doesn't absorb the proper wavelength of light to split. Feedback: Remember that the wavelength of light absorbed is associated with its energy, which must be high to split water. D

Consider Ohm's Law. Which of the following are correct?

A. Voltage is proportional to current B. Voltage is inversely proportional to current C. Current and resistance are proportional to each other D. All of these choices are correct A

Which type of widely used battery is not rechargeable?

A. Zinc-manganese alkaline B. Lithium-ion C. Lead-acid (storage batteries) D. Nickel-cadmium (NiCad) Feedback: One of these would be found as disposable flashlight batteries, while the others are in hand tools or computers. A

The opposite of a galvanic cell is

A. a battery. B. an electrolytic cell. C. a fuel cell. D. a photovoltaic (solar) cell. Feedback: Electricity is an input to this type of cell-hence its name. B

Chemical energy is converted directly into electrical energy in

A. a galvanic cell. B. an electrical power plant. C. an electrolytic cell. D. an automobile's engine. Feedback: Only one of these that has energy as output is electrical and not mechanical in nature. A

During the chemical reaction in an electrochemical cell,

A. a substance is oxidized and gains electrons. B. electrons travel from the cathode to the anode. C. oxidation takes place alone, without an accompanying reduction. D. oxidation occurs at the anode. Feedback: This is the black lead. D

The Prius, a hybrid car produced by Toyota, uses a battery that its maker claims should not have to be recharged or replaced during the lifetime of the car. The type of battery used in the Prius is

A. alkaline. B. lead acid. C. nickel-cadmium. D. nickel-metal hydride. Feedback: This is the most common advanced battery. It has not been on the market for more than a decade. D

In an electrochemical cell, the anode is

A. the electrode at which oxidation takes place. B. the material used to connect the two half cells to each other. C. always used up before the cathode. D. never a metal. Feedback: The anode is often a metal and it loses electrons. A

How do the interactions that are broken in water when it is boiled compare with those broken when water is electrolyzed?

A. Boiling water breaks intermolecular attractions and electrolysis breaks covalent bonds B. Boiling water breaks covalent bonds and electrolysis breaks intermolecular attractions C. Boiling water and electrolysis of water break covalent bonds D. Boiling water and electrolysis of water break intermolecular forces Feedback: Remember that covalent bonds consist of shared electrons. A

In this electrochemical cell, the reduction half reaction is

A. Cu2+(aq) + 2 e¯-> Cu(s) B. Zn(s) -> Zn2+(aq) + 2 e¯ C. Zn(s) -> Cu(s) D. Cu2+(aq) -> Zn2+(aq) Feedback: Reduction is gain of electrons. A

What condition must be met for a battery to be rechargeable?

A. Either its anode or its cathode must generate a gas as a result of the electrochemical reaction B. It must generate electricity via an acid-base reaction rather than via an oxidation-reduction reaction C. The battery must be open to the outside so that it can vent any internal pressure that builds up from gases within it D. The electrochemical reaction of the battery must be reversible Feedback: The reactions must be run in reverse to recharge a battery. D

What moves in the salt bridge from the cathode to the anode?

A. Electrons B. Zn+2 ions C. Cu+2 ions D. Anions Feedback: These move to balance the negative charge that flows in the wire. D

The aluminum-air battery is being considered for use in automobiles. In this battery, aluminum metal undergoes oxidation to Al3+ ions and forms Al(OH)3. O2 from the air undergoes reduction to OH¯ ions. Which half-reaction occurs at the anode?

A. Formation of OH¯ ions from O2 B. Capturing O2 from the air so that it may form the OH¯ ions C. Formation of Al3+ ions from aluminum D. Reaction of Al3+ ions with hydroxide ions to produce Al(OH)3 Feedback: Remember that oxidation is at the anode. C

How does using hydrogen as the fuel in an electric power plant compare with using hydrogen as the fuel in a fuel cell?

A. H2 used as a fuel in a power plant must be more pure than the H2 used in a fuel cell B. Burning H2 in a power plant produces many more pollutants than using H2 in a fuel cell C. A fuel cell using hydrogen operates at a higher overall efficiency than would a power plant burning hydrogen as a fuel D. Using H2 in a fuel cell generates far more heat than burning it in a power plant Feedback: Remember that much energy is lost as heat in combustion reactions. C

Why is it so expensive to ship hydrogen as a liquid as is often done with other gas?

A. Hydrogen is very heavy to ship B. Hydrogen is very dense to ship C. Hydrogen has to be shipped at a very low temperature D. Hydrogen in very flammable Feedback: Remember that things with low molar mass have low boiling points. C

A NiCd battery uses nickel and cadmium to produce a potential difference. Using these equations, answer the following questions. I. 2NiO(OH) (s) + 2H2O (l) + 2 e¯ -> 2Ni(OH)2 (s) + 2 OH¯ (aq) II. Cd(s) + 2OH¯ (aq) -> Cd(OH)2 (s) + 2e¯ III. Cd (s) + 2NiO(OH) (s) + 2 H2O (l) -> 2 Ni(OH)2 (s) + Cd(OH)2 (s) Which equation represents what takes place at the anode?

A. I B. II C. III D. I and II Feedback: Remember that oxidation is loss of electrons and happens at the anode. B

Which equation best represents the reduction half-reaction?

A. I B. II C. III D. I and II Feedback: Remember that reduction is loss of electrons at the cathode. A

Which equation represents the whole chemical reaction within the galvanic cell?

A. I B. II C. III D. I and II Feedback: Remember that the overall reaction must be both an oxidation and a reduction to complete the circuit. C

How does the reaction of hydrogen and oxygen to produce energy in a fuel cell differ from their interaction during the direct combustion of hydrogen and oxygen? I. The direct combustion of hydrogen and oxygen produces several different products, whereas the fuel cell produces only water II. Much less heat energy is produced in a fuel cell than via direct combustion of hydrogen and oxygen III. In the fuel cell, there is an oxidation-reduction reaction between hydrogen and oxygen. In the direct combustion of hydrogen and oxygen, there is no such reaction IV. It is much easier to control the hydrogen and oxygen during direct combustion than during their reaction in a fuel cell

A. I and II only B. I, II, and III only C. I, II, III, and IV D. I and III only Feedback: Combustion can be explosive and leads to unnecessary loss of energy as heat. B

Which is not an advantage of using a solid electrolyte in a fuel cell?

A. It is impermeable to liquids and gases and will keep the fuel and oxidizer separated B. It cannot dry out and will allow the fuel cell to operate at higher temperatures than one that uses water as part of the proton transfer mechanism C. It may use various fuels other than hydrogen gas, the fuel of choice in systems using water as part of the proton transfer mechanism D. It eliminates the need for an oxidant; only a fuel is required Feedback: Electrolytes are only for conducting electricity. D

What is the purpose of the hot KOH solution in the fuel cell?

A. It is the product of the reaction between the hydrogen, the oxygen, and the electrodes B. It keeps the electrodes conditioned and ready to work at high efficiency C. It is part of the acid-base reaction that generates the electricity in most fuel cells D. It maintains electroneutrality by working as an electrolyte; allowing transfer of ions between the half cells where the hydrogen and oxygen react Feedback: There always must be charge balance in an electrochemical cell. D

Which is not a necessary consideration for a battery designed to run a cell phone or portable MP3 player?

A. It must develop a useful level of electrochemical potential B. It must run for a reasonable amount of time C. It must use liquid, aqueous solutions D. It must be fairly light in weight Feedback: As long as batteries are sealed the phase of material in the battery should not matter. C

Which of the following automotive energy storage devices would give rise to the fastest acceleration from zero to 60 mph?

A. Li-ion rechargeable batteries B. Fuel cells C. NiMH rechargeable batteries D. Supercapacitors D

Which has not been suggested as a reasonably practical way to store large amounts of hydrogen in relatively small spaces for its use as a fuel?

A. Liquefy hydrogen under pressure and store it much as we do with liquefied natural gas today B. Absorb hydrogen onto activated charcoal; then heat the mixture to release the hydrogen C. Store it in the form of ionic metal hydrides, such as LiH, which release hydrogen gas when they react with water D. Encapsulate hydrogen molecules in fullerene molecules (large, carbon-based molecules that can act like cages) that may be heated later to release the hydrogen Feedback: Hydrogen cannot be used like natural gas A

Very small mercury batteries have been made and used in a multitude of applications. Why have they been replaced by other kinds of batteries for most applications?

A. Mercury has become far too expensive to use in batteries B. Mercury is poisonous and difficult to dispose of C. These batteries cannot generate enough current for any modern devices D. Though they may be made very small, they are far too heavy to use in most applications Feedback: Remember that considerations outside the electrochemical reaction itself have to be taken into account. B

Reforming processes can store hydrogen fuel in a liquid form as another molecule. Which of the following cannot be reformed into hydrogen?

A. Methanol B. Gasoline C. Diesel D. Carbon dioxide Feedback: The molecule must contain hydrogen atoms to be reformed into hydrogen. D

Which of the following statements is not true about PEM fuel cells?

A. PEM fuel cells rely on inexpensive catalysts B. PEM fuels cells are cleaner than gasoline powered vehicles C. PEM fuel cells have safe and efficient fuel storage D. PEM fuel cells have limited driving range A

Batteries are still preferred over supercapacitors for portable electronic applications. What factor(s) give rise to this preference?

A. Supercapacitors have low energy densities B. Supercapacitors are charged much more quickly than batteries C. Supercapacitors have virtually unlimited cycle lives D. All of these choices are correct A

What is the primary determinant of the voltage developed by a battery?

A. The nature of the materials in the reaction B. The age of the battery C. The overall size of the galvanic cells D. The size of the electrodes Feedback: There is no way to alter the voltage in a cell but to use different anode and cathode. A

Which is the cathode in this galvanic cell?

A. The solid zinc electrode B. The Zn2+(aq) ions in the 1 M solution C. The solid silver electrode D. The Ag+(aq) ions in the 1 M solution Feedback: Reduction and gain of electrons occur at the cathode. C

A major advantage of a fuel cell over a standard battery is that

A. as long as oxygen and fuel are supplied, a fuel cell will not run down like a battery will. B. a fuel cell generates electricity without the need for an oxidation-reduction reaction. C. a fuel cell is 100 percent efficient at generating electricity, whereas a battery is less than 1 percent efficient. D. as it generates electricity, a fuel cell produces more fuel than it uses. Feedback: Remember that batteries must be recharged and that nothing is 100 percent efficient. A

As fuel cells become more widely accepted and are used more, we will

A. become less dependent on electrical energy. B. become more dependent on fossil fuels and less dependent on renewable resources for power generation. C. be able to generate electricity in places where we cannot now do so. D. use coal as our primary energy source. Feedback: Think about these are more versatile batteries with continuous fuel supplied. C

The current through a wire is most closely related to the

A. energy of the electrons flowing through the wire. B. type of electrons flowing through the wire. C. rate of electron flow through a wire. D. oxidation potential of the electrons flowing through the wire. Feedback: Current has the unit Coulomb/s which is an ampere. C

In general, a modern hybrid vehicle is less polluting than a standard vehicle because it runs on both

A. gasoline engine and an electric motor run by a rechargeable battery. B. gasoline engine and a fuel cell. C. fuel cell and an electric motor run by a rechargeable battery. D. gasoline engine and a cleaner diesel engine. Feedback: Remember that running on electric power does not lead to tailpipe gasses. A

At present, it will be difficult and perhaps inappropriate to develop an economy based on burning hydrogen rather than natural gas or gasoline because

A. hydrogen is a dirty fuel. Burning hydrogen produces significantly more pollutants than burning natural gas or gasoline. B. hydrogen is not an efficient fuel. Per gram, hydrogen has about the lowest heat of combustion of any known substance, much lower than natural gas or gasoline. C. although hydrogen is abundant, pure hydrogen is not found naturally on earth. Hydrogen is difficult or expensive to isolate and collect. D. being such a light element, hydrogen will not flow through pipelines the way natural gas or gasoline do. Hydrogen cannot easily be delivered from where it is produced to the places where it is needed. Feedback: Remember that hydrogen is an excellent fuel, but has financial barriers to it being commonly used. C

For safety and other practical reasons, the most logical use for hydrogen as a fuel in the near future is

A. in an electric power plant. B. in a fuel cell. C. for running an automobile. D. for nuclear fusion. Feedback: One of these is already in use and is pollution-free. B

Whenever a substance is oxidized,

A. it is called the oxidizing agent. B. some other substance must be reduced. C. it gains electrons. D. hydronium ions are produced. Feedback: Loss of electrons is oxidation and those electrons are gained by another substance. B

What are the typical units for specific energy?

A. mAh/g B. W/kg C. Wh/kg D. kWh C

Electrolysis is a process that

A. produces an electrical current while decomposing water into hydrogen gas and oxygen gas. B. requires an electrical current to decompose water into hydrogen gas and oxygen gas. C. produces heat energy while decomposing water into hydrogen gas and oxygen gas. D. requires heat energy to decompose water into hydrogen gas and oxygen gas. B

Batteries must be used in addition to solar cells when generating household electricity because

A. solar cells can generate electricity only via the output of a battery. B. solar cells can generate only a small fraction of the total energy needed by a household at any one time. C. solar cells generate so much electricity that they will overheat if they cannot transfer the excess electricity somewhere to dissipate the extra heat. D. batteries must store and then supply the energy when sunlight is not available. Feedback: The sun is not out in a cloudless sky 24 hours a day. D

A fuel cell does not run down like a standard battery because

A. the reactants in a battery must be stored inside the battery, whereas the reactants for a fuel cell flow in as needed. B. a fuel cell continually recycles the same electrons, whereas a battery must continually generate new ones. C. a battery is completely dependent upon oxidation-reduction reactions, whereas a fuel cell depends on acid-base reactions. D. a battery has many moving parts, whereas a fuel cell has none. Feedback: This is the same reason your car doesn't run down as long as you purchase gasoline. A

In a fuel cell,

A. there is oxidation, but no reduction. B. reduction takes place at the cathode. C. there is direct conversion of mechanical energy into electricity. D. a chemical reaction produces heat, which then produces electricity. Feedback: Remember that the electrochemical process in a fuel cell is the same as in a regular battery. B