Chem 1020 -Ch 8. "Batteries"

A(n) _____ cell converts the energy released in a spontaneous chemical reaction into electrical energy.

Galvanic

A true battery is a collection of _____ cells that are wired together.

galvanic

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

Fe2+ → Fe3++ e-

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

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

-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.
-A half-reaction shows the electrons gained by the reactants in a galvanic cell.
-A half-reaction shows the electrons lost by the reactants in a galvanic cell.

True or False: Benjamin Franklin fabricated the first functional battery, the voltaic pile.

False

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)

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

spontaneous chemical

The oxidation state of an element ________.

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

Which of the following equations represents a reduction half-reaction?

2H+ + 2e- → H2

Reason:
Correct. Each H+ ion gains an electron in this process.

The species oxidized shows a(n)

increase in oxidation state

The species reduced shows a(n)

decrease in oxidation state

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

half-reaction

Consider the following balanced chemical equation:
2 S2O32- (aq) + I2 (aq) → S4O62- (aq) +2 I- (aq)
Which of the equations given below is the balanced reduction half-reaction for this equation?

I2 (aq) + 2 e- → 2I- (aq)

Consider the following two balanced cell half-reactions:
Cl2 (g) + 2 e- → 2 Cl- (aq)
S2- (aq) → S (s) + 2 e-
What is the overall balanced cell equation?

Cl2 (g) + S2- (aq) → 2 Cl- (aq) + S (s)

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

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

Which of the following options correctly describe electricity and its production by a galvanic cell? Select all that apply.

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

Consider the following balanced chemical equation:
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
Which of the following is the correct oxidation half-reaction for the above equation?

Fe (s) → Fe2+ (aq) + 2 e-

The difference in electrochemical potential between two electrodes of an electrochemical cell is called the____________, of the cell, measured in____________

voltage, volts

The ability of a resistor to slow the flow of electrons through an external circuit ______. (Select all options that complete this sentence correctly.)

-is called resistance
-has the symbol R

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

Electrodes are _____.

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

The rate of electron flow in a cell, measured in amperes, is called the cell _____.

current

A _____ slows the flow of electrons through an electrical circuit.

resistor

Ohm's Law relates voltage, resistance, and electrical current and is given by the formula ______.

V=I x R

In any electrochemical cell (including galvanic cells) oxidation occurs at the _____.

Anode

Reduction occurs at the _____ in a galvanic cell.

cathode

What oxidation state of iron is not possible?

+7

The voltage of a battery is affected by _____. Select all that apply.

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

Which of the following options correctly describe the cathode in a galvanic cell? Select all that apply.

-Reduction occurs at the cathode
-The cathode receives electrons from the anode.

The ability of an electrochemical cell to sustain a flow of electrons is called its ______.

Capacity

Alkaline batteries are called "alkaline" because _____.

operate in a basic medium

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

-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 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.

The capacity of an electrochemical cell _______. (Select all that apply.)

-reflects how long the cell can operate
-relates to its ability to sustain the flow of electrons
-is higher for larger cells

A typical alkaline battery exploits reactions involving _____ and _____.

zinc and manganese

In a Ni-Cd battery, which of the following is oxidized at the anode?

Cd

The voltage of a battery is affected by _____. Select all that apply.

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

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

mAh

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

True or false: An electrolyte must be used in a galvanic cell.

True

A dry cell battery _______.

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

Which of the following options correctly describe a modern lead-acid automobile battery? Select all that apply.

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

Why does a battery require a separator?

Direct contact between cathode and anode causes a short circuit.

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

electrolyte or salt bridge

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

Which of the following are some applications for lead-acid batteries? (Select all that apply.)

-electric scooters
-automobiles
-forklifts

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

lithium is extremely lightweight

True or false: An electrolyte must be used in a galvanic cell.

True

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.

gravimetric, volume

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

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

Which of the following are important attributes for the battery of electric vehicles? (Select all that apply.)

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

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

False

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

super capacitor

Which of the following statements correctly describe the reactions occurring in Li-ion batteries? (Select all that apply.)

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

The build-up of static electrical charge on a capacitor is called ______.

capacitance

Which of the following options correctly describe supercapacitors and rechargeable lithium-ion batteries? Select all that apply.

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

Supercapacitors

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

A battery or capacitor with a high power density ________.

delivers power quickly

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

Shorter charging time

Which of the following options correctly describe the effects of charging and recharging lithium ion batteries? Select all that apply.

-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.

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

Which of the following options correctly describe the power system of a hybrid electric vehicle (HEV)? Select all that apply.

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

Which of the following are some applications for supercapacitors? (Select all that apply.)

-Digital camera flash lighting
-Medical defibrillators

How can hydrogen be used as a fuel?

Hydrogen burns in oxygen to produce H2O and heat.

Which of the following options correctly describe hydrogen and methane fuels? Select all that apply.

-Both fuels are flammable gases.
-H2 produces fewer pollutants than CH4 when burned.
-H2 releases almost three times as much energy per gram as CH4 when burned.

A fuel cell converts ______.

the chemical energy of a fuel directly into electricity without burning the fuel

A hydrogen fuel cell produces energy _____ rapidly and with ______ efficiency than the production of energy in a conventional combustion engine.

less, higher

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

Which of the following options correctly describe hydrogen-rich fuels? Select all that apply.

-These fuels can be used to power fuel cell vehicles, which have an onboard reformer.
-These fuels are converted into H2 by a device that uses heat, pressure, and catalysts to run a chemical reaction.
-Liquid hydrogen-rich fuels include methanol and ethanol.

Fuel cells are a form of distributed generation since they generate electricity _____.

on site where it is used

In both fuel cells and conventional batteries _____.

an electrochemical reaction produces energy

H2 gas can be stored using metal _____ such as LiH, which absorb H2 molecules into the spaces within their crystal structure.

hydrides

Which of the following options correctly describe the role of metal hydrides for the storage and transportation of hydrogen gas? (Select all that apply.)

-When placed under high pressure the metal hydride acts like a sponge to absorb H2 molecules.
-Metal hydrides are selective and can separate H2 from larger molecules such as O2, CO, and CO2.