chapter 8 chem hw

What oxidation state of iron is not possible?

+7 anything but +2,3,4

Which of the following options correctly describe a half-reaction? (Select all that apply.)

-A half-reaction shows the electrons lost by the reactants in a galvanic cell. -A half-reaction shows the electrons gained by the reactants in a galvanic cell. -The overall process occurring in a galvanic cell includes both an oxidation and a reduction reaction. The two parts are each known as half-reactions.

Which of the following options correctly describe environmental consequences that result from the production of batteries?

-Acid rain is produced as a result of SO2 release during the metal ore refining process. -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.

How batteries work

-Batteries take advantage of spontaneous redox reactions (Galvanic cells) -Rather than allowing the redox reaction to occur directly, batteries have the two halves of a redox reaction physically separated, forcing electrons to travel through an external circuit -Electron transfer occurs through electrodes; The Anode is where Oxidation takes place; The Cathode is where Reduction takes place.

Which of the following options correctly describe a rechargeable battery? Select all that apply.

-Both reactants and 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.

Supercapacitors: the batteries of the future?

-Capacitors store energy in the form of static charge rather than redox reactions -Supercapacitors store a significant amount of charge that can be released as electrical energy.

Which of the following are some applications for supercapacitors?

-Digital camera flash lighting -Medical defibrillators

Which of the following statements correctly describe the reactions occurring in Li-ion batteries?

-During charging, Li+ ions move from the cathode to anode. - Li+ shuttles between cathode and anode electrodes during charging and discharging.

Which of the following are some applications for lead-acid batteries?

-Electric scooters -Automobiles -Forklifts

Which of the following options correctly describe electricity and its production by a galvanic cell?

-Electricity is produced by the movement of electrons through an external circuit. -The flow of electrons from one region to another is driven by differences in potential energy.

Portable sources of electricity

-Electricity is the flow of electrons. Heat can be converted into electricity in a powerplant (combustion reaction and nuclear reactions), Light can be converted into electricity with photovoltaic cells -We often need to store energy. Power "on the go" (cell phones, laptops, etc.), Transportation (electric cars), Storing intermittent renewable energy sources (wind and solar) -Batteries convert chemical potential energy into electricity.

Half reactions

-Electrons are not shown explicitly in the overall balanced redox reaction. -Splitting the reaction into half reactions shows what is being oxidized and what is being reduced. -An oxidation and reduction always occur together.

Batteries in hybrid cars

-Hybrid cars use a nickel-metal hydride battery along with an internal combustion engine -Brakes are used to recharge battery

Which of the following are important attributes for the battery of electric vehicles?

-It must have a low density. -It must have a long operating range per charge.

Why is it a bad idea to dispose of automobile batteries in landfills? Select all that apply.

-Leaching of chemicals from the batteries will eventually result in groundwater contamination. -The metals in the batteries will become too widely dispersed to effectively mine for reuse. -Toxic materials such as PbO2 will be able to enter the environment.

Which of the following are environmental "costs" of batteries?

-Lithium metal mining generates significant waste. -There are currently no effective methods for full battery recycling. -Mining and purifying metals releases air pollutant gases.

Which of the following options correctly describe the relationships between the Group IA metals?

-Na and K are more abundant than Li in the Earth's crust. -Li is lighter than Na. -Li, Na, and K are highly reactive metals.

Which of the following options correctly describe the effects of charging and recharging lithium ion batteries?

-Over-discharging the battery causes some Li+ ions to react irreversibly with the cathode material. -Battery capacity decreases if the battery is discharged to less than 10%. -Each time the battery is discharged and recharged, the structure of of the electrode surfaces changes.

Which of the following options correctly describe the processes occurring at the anode of a galvanic cell? Select all that apply.

-Oxidation takes place at the anode. -The anode is the source of electrons in the current flow.

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.

Which of the following options correctly describe the power system of a hybrid electric vehicle (HEV)?

-Regenerative braking is used to charge the batteries during braking and deceleration. -The gasoline engine assists the electric motor during normal driving. -The electric motor draws power from the nickel-metal hydride batteries to power the vehicle at low speeds.

Which of the following will cause the capacitance of a charged-plate supercapacitor to increase? (Select all that apply.)

-Smaller separation between the charged plates. -Greater surface area of the charged plates.

Which of the following options correctly describe cell voltage? Select all that apply.

-Some cells can last as long as ten years. -Cell voltage is a function of the chemicals used to construct the battery. -Higher voltages are possible by connecting cells.

Which of the following options correctly describe supercapacitors and rechargeable lithium-ion batteries?

-Supercapacitors have much higher power densities than Li-ion batteries. -Supercapacitors operate effectively over a wider temperature range than Li-ion batteries.

Batteries in EV cars

-The Tesla Model S uses a lithium ion battery - Li-ion batteries are much more light weight than traditional batteries.

Which of the following options correctly describe a modern lead-acid automobile battery?

-The electrolyte in a lead-acid battery is H2SO4. - 12-V lead-acid batteries are made up of six cells that each generate 2 V. -The anode and the cathode are both solids (Pb and PbO2).

Which of the following options correctly describe the separator in any battery? Select all that apply.

-The separator may be an electrolyte solution. -The separator in modern batteries is frequently a semipermeable membrane that allows ion flow. -The separator retains charge neutrality during battery operation.

Match each species involved in a redox reaction with the correct description. Instructions

-The species oxidized shows a(n) → increase in oxidation state. -The species reduced shows a(n) → decrease in oxidation state.

Which of the following options correctly describe the term current?

-The unit of current is the ampere. -Current is the rate of electron flow in a circuit.

Batteries in cars

-Traditional cars have lead-acid batteries provide small amount of power to help start the engine -Battery recharges from power supplied by the internal combustion engine.

The waterfall analogy

-Voltage is the difference in electrical energy energy between two points in a circuit -Current is the rate of flow of charge -Resistance is a measure of the opposition of charge flow.

Current limitations to rechargeable batteries

-Weight -Lost capacity with charge-recharge cycles ("memory effect") -Time to charge -Cost -And don't forget: an electric car is only a green as the power source used to charge it!

The voltage of a battery is affected by _____.

-its chemical composition -the number of electrochemical cells wired together

Match each type of galvanic cell listed below with its typical application.

-lead-acid → automobile batteries -alkaline → flashlights and small appliances -lithium-iodine → pacemakers -nickel-metal hydride (NiMH) → hybrid vehicle batteries

A typical alkaline battery exploits reactions involving _____ and _____.

-manganese -zinc

Supercapacitors ______

-may release stored charge as electrical energy -store energy in the form of a static electrical charge -consist of two electrodes immersed in an electrolyte

The oxidation state of an element ________.

-reflects the way electrons are transferred during a reaction -reflects its charge if it is present as an ion -is determined by the way it is bonded

Compared to conventional gasoline-fueled cars, hybrid electric vehicles:

-release fewer pollutants over the lifetime of the vehicle. -use less gasoline.

Consider the following two half-reactions: Fe2+ (aq) → Fe3+ (aq) + e- Cl2 (g) + 2 e- → 2 Cl- (aq) What is the overall balanced equation that may be constructed from these two half-reactions?

2 Fe2+ (aq) + Cl2 (aq) → 2 Fe3+ (aq) + 2 Cl- (aq)

Which of the following equations represents a reduction half-reaction? Zn + 2H+ → Zn2+ + H2 2H+ + 2e- → H2 Zn → Zn2+ + 2e-

2H+ + 2e- → H2 e- on left side

How efficient are batteries?

90%

What about rechargeable batteries?

A battery acts as a galvanic cell when in use, generating electricity through a spontaneous reaction. Primary batteries are disposed of when they are "used up." -A battery acts as an electrolytic cell when charging, using external energy to force the reverse, nonspontaneous reaction to occur. Secondary batteries can be reused.

Oxidation States

Assigning oxidation states allows you to keep track of electrons in redox reactions. -The oxidation state of pure elements is always zero. -The oxidation state of a charged monoatomic ion is equal to its charge. -In molecules, H has an oxidation state of +1 and O has an oxidation state of -2.

Supercapacitors vs. batteries

Benefits of supercapacitors over batteries: Nearly limitless number of charging-recharging cycles, Faster time to charge, & Wider temperature range of use -Current limitation of supercapacitors: Lower energy density, Difficult to maintain a stable voltage from a supercapacitor, Discharge while not in use -Future development in supercapacitors and batteries will make renewable energy more practical and affordable.

Why does a battery require a separator?

Direct contact between cathode and anode causes a short circuit. A battery harnesses the flow of electrons from anode to cathode by connecting the electrodes with a wire. If the electrodes are in direct contact, this flow is short circuited and the battery cannot provide useful work.

Which of the following equations represents an oxidation half-reaction?

Fe2+ → Fe3++ e- e- right side

Which of the following is both the lightest of the four elements and the least abundant in the Earth's crust?

Li

Which of the statements below are benefits of using Li-ion batteries for automotive applications?

Lithium metal is extremely lightweight.

Redox reactions

Redox reactions involve the transfer of electrons from one thing to another. -The chemical species that supplies the electrons is oxidized -The chemical species that accepts the electrons is reduced.

Which of the following pollutants may be released into the environment during the production or incorrect disposal of batteries?

SO2 CO2 Toxic metals

Which of the following represents a benefit of supercapacitors, relative to Li-ion batteries?

Shorter charging time

how to Balance Redox reactions

To balance redox reactions, first split them up into half reactions and determine the number of electrons transferred. Fe + Zn2+ -> Fe2+ + ZnFe + Zn2+ -> Fe3+ + Zn

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

A dry cell battery _______

contains an electrolyte paste with just enough moisture to allow ions to flow

Ohm's Law is given by V=I·R. What quantity is indicated by the symbol "I"?

current

A battery or capacitor with a high power density ________.

delivers power quickly

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

Electrodes are _____.

electrical conductors within a cell that serve as sites for chemical reactions

Voltage is a measure of the _____.

electrical potential between two points in a circuit

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

A _____ is a solid or liquid substance added to a galvanic cell, which facilitates the passage of ions through the separator.

electrolyte or salt bridge

True or false: The anode of a Li-ion battery is commonly a metal oxide such as LiCoO2.

false Reason: A metal oxide such as LiCoO2 is the cathode.

A(n) _____ is a type of chemical equation that shows the electrons either lost or gained by the reactants.

half-reaction

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 (HEV)

The capacity of a battery is measured in which of the following units?

mAh

The _____ energy density of a battery measures stored charge in units of Wh/g. while the ______ energy density measures the stored charge in units of Wh/L.

mass; volume

Oxidation, or the loss of electrons, will result in an element becoming _____ positive. This element will show a(n) _____ in oxidation state. Reduction, the gain of electrons, will cause an element to become _____ positive and the element will show a(n) _____ in oxidation state.

more; increase; less; decrease

To track the transfer of electrons in both ionic and molecular substances, we assign a(n) ______ number to each element involved. This number reflects the charge the element would have if all bonds were ionic.

oxidation

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 (PHEV)

The ____ density refers to the time it takes for a battery to deliver its charge. In contrast, the ____ density refers to the stored capacity of the battery.

power; energy

A battery that employs electrochemical reactions that run in both directions is _____.

rechargeable

_______ braking is used to charge the battery in a hybrid vehicle during deceleration and braking.

regenerative

The loss of charge of a battery over time, when not connected to a power supply, is known as ______

self-discharge

A galvanic cell is a type of electrochemical cell that converts energy released from a _____ reaction into electrical energy.

spontaneous chemical

A device composed of electrodes immersed in electrolytes that stores electrical energy in the form of a static charge is called a(n) ______.

supercapacitor

Alkaline batteries are called "alkaline" because _____.

they operate in a basic medium

Priorities of batteries...

total energy, time to discharge/charge, cost of materials, size, efficiency, life span, durability