Exam #4 Prep

Question 1

Why does a fuel cell not “run down” like a standard battery?

Answer 1

the reactants in a battery must be stored inside the battery whereas the reactants for a fuel cell flow as needed

Question 2

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

Answer 2

the nature of the materials in the reaction

Question 3

What is the oxidation half-reaction?

Answer 3

Zn –> Zn^(2+) + 2e-

Question 4

What is the oxidation half-reaction?

Answer 4

Zn –> Zn^(2+) + 2e-

Question 5

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

Answer 5

be able to generate electricity where we cannot do so now

Question 6

Which has NOT been suggested as a reasonably practical way to store large amounts of H2 in small spaces?

Answer 6

liquify under pressure

Question 7

What is the max efficiency of a solar cell?

Answer 7

40%

Question 8

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

Answer 8

the mechanical motion of the engine drives an alternator that generates electricity to recharge the battery

Question 9

What battery shouldn’t have to be replaced in a hybrid car?

Answer 9

nickel metal hydride

Question 10

What metal is used to “dope” a n-type semiconductor?

Answer 10

arsenic

Question 11

What are necessary considerations for a battery designed to run a cell phone?

Answer 11

must develop a useful level of electrochemical potential, must “run” for a reasonable amount of time, must be lightweight

Question 12

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

Answer 12

batteries must store/supply energy when there is no sun

Question 13

Whenever a substance is oxidized…

Answer 13

another substance must be reduced

Question 14

Whenever a substance is oxidized…

Answer 14

another substance must be reduced

Question 15

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

Answer 15

boiling water breaks intermolecular attractions, electrolysis breaks covalent bonds

Question 16

What is the whole chemical reaction of a galvanic cell?

Answer 16

Cd(s) + 2NiO(OH)(s) + 2H2O)l) –> 2Ni(OH)2(s) + Cd(OH)2(s)

Question 17

PEM fuel cells….

Answer 17

• are cleaner than gasoline powered vehicles
• are safe/efficient fuel storage
• have a limited driving range

Question 18

Chemical energy is converted directly into electrical energy in a ….

Answer 18

galvanic cell

Question 19

How do you generate electricity in a solar cell when p-type and n-type semiconductors are placed in contact by a wire?

Answer 19

light shining on system must have enough energy to set electrons in motion from n-type to p-type

Question 20

A major advantage of fuel cells over batteries is…

Answer 20

as long as O2 and fuel are supplied, the fuel cell won’t “run down”

Question 21

Where does reduction take place in a fuel cell?

Answer 21

at the cathode

Question 22

Where does reduction take place in a fuel cell?

Answer 22

at the cathode

Question 23

The current through a wire is most closely related to the…

Answer 23

rate of electron flow through that wire

Question 24

How is wind energy related to the sun?

Answer 24

heat of sun drives large scale movements of air

Question 25

Difficult to develop an economy based on H2 because...

Answer 25

hydrogen is abundant, but pure H2 isn't natural on earth --> difficult and costly to isolate and collect

Question 26

What increases the efficiency of a photovoltaic/solar cell?

Answer 26

- replacing crystalline with non-crystalline silicon - increasing the number of alternating p and n-type layers of semiconductors - decreasing the thickness of each alternating p and n type layers of semiconductors

Question 27

Why doesn't water naturally split into H2 and O when in light?

Answer 27

water doesn't absorb the proper wavelength of light to split

Question 28

In an electrochemical cell, the anode is...

Answer 28

the electrode where oxidation occurs

Question 29

Semiconductors are more effective converters of solar radiation than metals because...

Answer 29

energy is sunlight gives valence electron in the semiconductor extra energy they need to "flow" through the solid

Question 30

Which has a lower melting point, HDPE or LDPE?

Answer 30

LDPE

Question 31

The regions of a polymer where the long polymer molecules are arranged neatly/tightly in a regular patter is called the _______

Answer 31

crystalline region

Question 32

The distinctive arrangements of atoms that impart characteristic chemical properties to the molecules that contain them are called _______

Answer 32

functional groups

Question 33

What does a peptide bond look like?

Answer 33

N=C

Question 34

What do the "Big Six" polymers have in common?

Answer 34

they are thermoplastics

Question 35

What are the molecules added to polymers to make them softer/more pliable?

Answer 35

plasticizers

Question 36

What are the molecules added to polymers to make them softer/more pliable?

Answer 36

plasticizers

Question 37

PET contains what sort of linage between monomer units?

Answer 37

ester

Question 38

Which raw material serves as source for most polymers?

Answer 38

crude oil

Question 39

What is an amine group?

Answer 39

NH2

Question 40

Which synthetic polymer has two forms (crystal and expandable)?

Answer 40

PS

Question 41

Which synthetic polymer has two forms (crystal and expandable)?

Answer 41

PS

Question 42

Skin, hair, muscle, and enzymes are all made of protein which is a natural polymer. What polymer?

Answer 42

polyamides

Question 43

What is electrolysis?

Answer 43

a process that requires an electrical current to break water into hydrogen gas and oxygen gas

Question 44

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

Answer 44

a fuel cell using hydrogen operates at a higher overall efficiency than would a power plant burning hydrogen as fuel

Question 45

Cellulose is classified as a...

Answer 45

condensation homopolymer

Question 46

Sunlight may be turned directly into electricity using _____

Answer 46

photovoltaic cells

Question 47

What is the oxidation half-reaction?

Answer 47

Zn --> Zn^(2+) + 2e-

Question 48

Whenever a substance is oxidized...

Answer 48

another substance must be reduced

Question 49

Where does reduction take place in a fuel cell?

Answer 49

at the cathode