CHEMLEC Chapter 7: Energy Storage
which of the following options correctly describe the cathode in a galvanic cell?
- reduction occurs at the cathode - the cathode receives electrons from the anode
what are the two main disadvantages of the production of hydrogen from methane (CH4)?
-CO2 (a greenhouse gas) is produced in addition to hydrogen -The process requires significant energy input
which of the following options correctly describe the operation of a photoelectrochemical cell, which could potentially harness the Sun's energy to produce H2?
-Dye particles on one electrode absorb light, causing their electrons to move higher energy states -electrons arrive at the cathode where they reduce H^+ ions to H2^+ -one electrode is made of Pt metal
what products are formed when hydrogen gas (H2) is burned in oxygen?
-H2O -heat
which of the following options correctly describe the relationships between the group IA metals?
-Li, Na, and K are highly reactive metals -Na and K are more abundant than Li in the Earth's crust -Li is lighter than Na
which of the following options correctly describe advantages of plug-in hybrid electric vehicles (PHEVs) as compared to conventional gasoline powered automobiles?
-PHEVs are less expensive to operate on a per-mile basis. -The electric energy provided by the battery decreases the direct emisions from the tallpipe
which of the following options correctly describe a half-reaction?
-a half reaction shows the electron lost by the reactants -the overall processes occurring in a galvanic cell includes both an oxidation and a reduction reaction. the two parts are each known as half-reactions -a half reaction shows the electrons gained by the reactants in a galvanic cell
which of the following options correct describe the effects of changing and recharging lithium ion batteries?
-battery capacity decreases if the battery is discharged less than 10% -over-discharging the battery cause some Li' ions to react irreversibly with the cathode material -each time the battery is discharged, the structure of the electrode surfaces changes.
which of the following options correctly describe a rechargeable battery?
-both reactants products are solids -the battery's lifetime is dependent on the breakdown of the separators -the battery's lifetime is dependent on the accumulation of impurities
which of the following options correctly describe cell voltage?
-cell voltage is a function of the chemicals used to construct the battery -some cells can last as long as ten years -higher voltages are possible by connecting cells
which of the following options correctly describe the term current?
-current is the rate of electron flow in a cell -the unit of current is the ampere
what features are desirable in order for a battery to be successful in the eyes of consumers?
-ease of recycling -affordability -long lifetime
which of the following options correctly describe and its production by a galvanic cell?
-electricity is produced by the moment of electrons through an external circuit -the flow of electrons from one region to another is driven by differences in potential energy
the ability of a resistor to slow the flow of electrons through an external circuit __________.
-has the symbol R -is called the resistance
the voltage of a battery is affected by __________.
-its chemical composition -the number of electrochemical cells wired together
which of the following options correctly describe the role of metal hydrides for the storage and transportation of hydrogen gas?
-metal hydrides are selective and can separate H2 from larger molecules such as O2, CO and CO2 -when placed under high pressure the metal hydride acts like a sponge to absorb H2 molecules
which of the following are potential naturally occurring sources of hydrogen gas?
-natural gas -water -methane
which two types of battery are currently used by hybrid electric vehicles (not including plug-in hybrids)?
-nickle-metal hydride battery -lithium-ion battery
which of the following options correctly describe the processes occurring at the anode of a galvanic cell?
-oxidation takes place at the anode -the anode is the source of electrons in the current flow
the capacity of an electrochemical cell __________.
-refers to its ability to sustain the flow of electrons -reflects how long the cell can operate -is higher for larger cells
the oxidation state of an element ___________
-reflects its charge if it is present as an ion -is determined by the way it is bonded -reflects the way electrons are transferred during a reaction
compared to conventional gasoline powered cars, hybrid electric vehicles __________.
-release fewer pollutants over the life of the vehicle -deliver better mileage in city driving -use less gasoline
which of the following options correctly describe the key features of a fuel cell?
-solid polymer electrolyte materials separate the reactants -the anode in a fuel cell simply acts as a conductor and does not participate in the oxidation reaction -H2 passes through the PEM and is oxidized to form two H^+ ions
which of the following options correctly describe supercapacitors and rechargeable lithium-ion batteries?
-supercapacitors operate effectively over a wider temperature range than Li-ion batteries -supercapacitors have much higher power densities than Li-ion batteries
which of the following factors may impact the cost (both economic and environmental) of a battery?
-the correct disposal of "dead" batteries may result in hazardous chemicals entering the environment -the metals in batteries are refined from ores and this requires energy -smelting often produces sulfur dioxide
which of the following options correctly describe the power systems of a hybrid electric vehicle (HEV)?
-the gasoline engine assist the electric motor during normal driving -regenerative braking is used to charge the batteries during braking and deceleration -the electric motor draws pwer from the nickle-metal hydride batteries to power the vehicle at low speeds
which of the following options correctly describe environmental consequences that result from the production of batteries?
-the mining of metal ores needed to produce batteries leaves mine tailings and other waste that must be cleaned up -lead-acid batteries may leak and release corrosive material into the environment -acid rain is produced as a result of SO2 release during the metal ore refining process
which of the following options correctly describe the separator in any battery?
-the separator retains charge neutrally during battery operation -the separator in modern batteries is frequently a semipermeable membrane that allows ion flow. -the separator may be an electrolyte solution
lithium ion batteries are better than batteries that use other alkali metals because __________.
-they are very light and ideal for portable applications -they typically provide higher voltages than other batteries
why is it a bad idea to dispose of automobile batteries in landfills?
-toxic materials such as PbO2 will be able to enter the environment -Leaching of chemicals from batteries will eventually result in ground water contamination -the metals in the batteries will become too widely dispersed to effectively mine for reuse
place the reactions that involve the production of H2 in a reformer in the correct order
1. CH3OH(I) ➡️ CH3OH(g) 2. CH3OH(g) ➡️ CO(g) + 2H2(g) 3. CO(g) + H2O(g) ➡️ CO2(g) + H2(g)
rank the following common galvanic cells in order of increasing voltage
1. Ni-Cd 2. alkaline 3. lead-acid 4. lithium-ion
consider the following two half-reactions: Fe^2+(aq) ➡️ Fe^3+(aq) + e^- Cl2(g) + 2e^- ➡️ 2Cl^-(aq) what is the overall balance equation that may be constructed from these two half-reactions?
2Fe^2+(aq) + Cl2(aq) ➡️ Fe^3+(aq) + Cl^-(aq)
which of the following equations represents a reduction half-reaction?
2H^+ + 2e^- ➡️ H2
match each type of electrochemical cell with the correct description
> A fuel cell - utilizes external source of fuel and oxidant > A conventional battery - requires no external source of fuel or oxidant > the electrodes participate in reactions - in a conventional battery > the electrodes simply serve as conductors - in a fuel cell
match each fuel with the correct description of its energy content and the products it forms when burned in oxygen
> H2 burns to form - H2O only > CH4 burns to form - CO2 and H2O > the energy from H2 combustion - is higher (124.5 kj/g) > the energy from CH4 combustion - is lower (50 kj/g)
match each type of energy-producing technology to the correct description
> H2 is the fuel in - a hydrogen fuel cell > Hydrocarbon fuels are used in - a combustion engine > A combustion engine produces - CO, CO2, H2O and energy > A hydrogen fuel cell produces - H2O and electricity
match each electrical device with the correct descriptions and features
> Supercapacitor - very short charging - lower voltage - higher specific power -lower specific energy >Lithium-ion battery -lower specific power -higher specific energy -higher voltage -longer charging time
match each component of an electrochemical cell with its correct description
> anode - a site which oxidation takes place and is therefore a source of electrons > cathode - a site at which reduction takes place and is therefore a site where electrons are received > electrode - an electrical conductor within a cell that serves as a site for chemical reaction
math each reaction that occurs in a typical lead-acid battery with the correct description
> discharging - Pb and PbO2 are converted to PbSO4 > charging PbSO4 is converted yo Pb and PbO2
match each process with the correct description
> oxidation - loss of electrons > reductions - gain of electrons
match each species in a redox reaction with the correct description
> the species oxidized shows a(n) - increase in oxidation state > the species reduced shows a(n) - decrease in oxidation state
Ohm's Law is given by V = I*R. match each quantity correctly to its meaning and symbol
>V -unit abbreviation V -measured in volts -voltage >I -current -measured in amperes -unit abbreviation A >R -measured in ohms -resistance -unit abbreviation Ω
match each reaction occurring in a Ni-Cd cell with the correct description.
>reaction at the anode - Cd(s) + 2OH(aq) ➡️ Cd(OH)2(s) + 2e^- >reaction at the cathode - 2NiO(OH)(s) + 2H2O(I) + 2e^- ➡️ 2Ni(OH)2(s) + 2OH^-(aq) >overall cell equation - CD(s) +2NiO(OH)(s) + 2H2O(I) ➡️ 2Ni(OH)2(s) + Cd(OH)2(s)
consider the following two half-reactions: Cl2(g) + 2e^-➡️ 2Cl^-(aq) S^2-(aq) ➡️ S(s) + 2e^- what is the overall balance cell equation?
Cl2(g) + S^2- ➡️ 2Cl^-(aq) + S(s)
consider the following balanced chemical equation: Fe(s) + CuSO(aq) ➡️ FeSO4(aq) + Cu(s) which of the following is the correct oxidation half-reaction for the above equation?
Fe(s) ➡️ Fe^2+(aq) + 2e^-
which of the following represents an oxidation half-reaction?
Fe^2+ ➡️ Fe^2+ + e^-
consider the following balanced chemical equation: 2S2O3^2-(aq) + I2(aq) ➡️ S4O6^2-(aq) + 2I^-(aq) which of the equations given below is the balanced reduction half-reaction for this equation?
I2(aq) + 2e^- ➡️ 2I^-(aq)
which of the following is both the lightest of the four elements and the least abundant in the earth's crust?
Li
in any electrochemical cell (including galvanic cells) oxidation occurs at the __________.
anode
a true __________ is made up of several galvanic (voltaic) cells that are wired together
battery
a hybrid electric vehicle (HEV) is propelled by ____________.
both a conventional gasoline engine and an electric motor run on batteries
the build-up of static electrical charge on a capacitor is called __________.
capacitance
the ability of an electrochemical cell to sustain a flow of electrons is called its __________.
capacity
the rate of electron flow in a cell, measured in amperes, is called the cell ___________.
current
a battery or capacitor with a high power density __________.
delivers power quickly
voltage is a measure of the ____________
difference in electrochemical potential between the two electrodes in a galvanic cell
why does a battery require a separator?
direct contact between cathode and anode causes a short circuit
batteries such as rechargeable Ni-Cd batteries are referred to as ___________ cells because they contain an electrolyte that is mobilized as a paste rather than an electrolyte solution.
dry
an electrolytic cell converts ___________
electrical energy into chemical energy
the flow of electrons through an external circuit produces __________, which is the flow of electrons from one region to another driven by a difference in ___________ energy
electricity; potential
the decomposition of water into H2 and O2 by passing an electrical current through it is called __________.
electrolysis
the equation voltage*# of movable li^+ ions in electrodes / total battery mass or volume expresses the __________ of a lithium ion battery
energy density
the main disadvantage in using hydrogen as fuel source is __________.
flammability
A(n) __________ cell is an electrochemical cell that produces electricity by converting the chemical energy of a fuel directly into electricity without burning the fuel.
fuel
a(n) __________ cell converts the energy released in a spontaneous chemical reaction into electrical energy
galvanic
a vehicle that is propelled by a combination of a conventional gasoline engine and an electric motor run by batteries is a __________.
hybrid electric vehicle
H2 gas can be stored using metal __________ such as LiH, which absorb H2 molecules into the spaces within their crystal structure
hydrides
How can hydrogen be used as a fuel?
hydrogen burns in oxygen to produce H2O and heat
what is the major disadvantage of burning hydrogen as source of energy?
hydrogen is extremely flammable and can explode when mixed directly with oxygen
a typical alkaline battery exploits reactions involving __________ and __________
manganese; zinc
fuel cells are a form of distributed generation since they generate electricity __________.
on-site right where it is used
a process in which a species loses electrons is known as __________, whereas a process in which a species gains electrons is known as __________.
oxidation; reduction
in a fuel cell, H2 is ___________ to form 2H^+ as it passes through the PEM. these H^+ ions combine with O2 at the cathode in a ___________ half-reaction to form H2O
oxidized; reduction
a vehicle that uses rechargeable batteries for short commutes to run an electric motor and switches to a combustion engine to travel longer distances is a ____________.
plug-in hybrid electric vehicle
a battery that employs electrochemical reactions that run in both directions is __________.
rechargeable
a __________ slows the flow of electrons through an electrical circuit
resistors
supercapacitors and some rechargeable batteries tend to lose charge over time. this problem is known as __________.
self-discharge
the process of heating and chemically processing an ore, which is called __________ or refining often results in the release of __________ dioxide
smelting; sulfur
a device composed of electrodes immersed in electrolytes that stores electrical energy in the form of a static charge is called a(n) ___________.
supercapacitor
a fuel cell converts __________.
the chemical energy of a fuel directly into electricity without burning the fuel
alkaline batteries are called "alkaline" because ___________.
they operate in a basic medium
from an environmental perspective, what is the most important advantage that hybrid electric vehicles have over conventional gasoline-powered cars?
they produce fewer pollutants over the lifetime of the vehicle
one way to generate H2 for fuel cells is by the decomposition of water. the most economical way of generating the heat required to decompose water is to __________.
use a photoelectrochemical cell
the difference in electrochemical potential between in two electrodes of an electrochemical cell is called the __________ of the cell, measured in __________.
voltage; volts