Exam #4 Prep Flashcards
Why does a fuel cell not “run down” like a standard battery?
the reactants in a battery must be stored inside the battery whereas the reactants for a fuel cell flow as needed
What is the primary determinant of the voltage developed by a battery?
the nature of the materials in the reaction
What is the oxidation half-reaction?
Zn –> Zn^(2+) + 2e-
What is the oxidation half-reaction?
Zn –> Zn^(2+) + 2e-
As fuel wells become more widely accepted and are used more, we will…
be able to generate electricity where we cannot do so now
Which has NOT been suggested as a reasonably practical way to store large amounts of H2 in small spaces?
liquify under pressure
What is the max efficiency of a solar cell?
40%
Why can the lead-acid batteries in cars generate electricity for several years before running down?
the mechanical motion of the engine drives an alternator that generates electricity to recharge the battery
What battery shouldn’t have to be replaced in a hybrid car?
nickel metal hydride
What metal is used to “dope” a n-type semiconductor?
arsenic
What are necessary considerations for a battery designed to run a cell phone?
must develop a useful level of electrochemical potential, must “run” for a reasonable amount of time, must be lightweight
Batteries must be used in addition to solar cells when generating household electricity because….
batteries must store/supply energy when there is no sun
Whenever a substance is oxidized…
another substance must be reduced
Whenever a substance is oxidized…
another substance must be reduced
How do interactions that are broken in water when it is boiled compare to those when it is electrolyzed?
boiling water breaks intermolecular attractions, electrolysis breaks covalent bonds
What is the whole chemical reaction of a galvanic cell?
Cd(s) + 2NiO(OH)(s) + 2H2O)l) –> 2Ni(OH)2(s) + Cd(OH)2(s)
PEM fuel cells….
- are cleaner than gasoline powered vehicles
- are safe/efficient fuel storage
- have a limited driving range
Chemical energy is converted directly into electrical energy in a ….
galvanic cell
How do you generate electricity in a solar cell when p-type and n-type semiconductors are placed in contact by a wire?
light shining on system must have enough energy to set electrons in motion from n-type to p-type
A major advantage of fuel cells over batteries is…
as long as O2 and fuel are supplied, the fuel cell won’t “run down”
Where does reduction take place in a fuel cell?
at the cathode
Where does reduction take place in a fuel cell?
at the cathode
The current through a wire is most closely related to the…
rate of electron flow through that wire
How is wind energy related to the sun?
heat of sun drives large scale movements of air
Difficult to develop an economy based on H2 because…
hydrogen is abundant, but pure H2 isn’t natural on earth –> difficult and costly to isolate and collect
What increases the efficiency of a photovoltaic/solar cell?
- 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
Why doesn’t water naturally split into H2 and O when in light?
water doesn’t absorb the proper wavelength of light to split
In an electrochemical cell, the anode is…
the electrode where oxidation occurs
Semiconductors are more effective converters of solar radiation than metals because…
energy is sunlight gives valence electron in the semiconductor extra energy they need to “flow” through the solid
Which has a lower melting point, HDPE or LDPE?
LDPE
The regions of a polymer where the long polymer molecules are arranged neatly/tightly in a regular patter is called the _______
crystalline region
The distinctive arrangements of atoms that impart characteristic chemical properties to the molecules that contain them are called _______
functional groups
What does a peptide bond look like?
N=C
What do the “Big Six” polymers have in common?
they are thermoplastics
What are the molecules added to polymers to make them softer/more pliable?
plasticizers
What are the molecules added to polymers to make them softer/more pliable?
plasticizers
PET contains what sort of linage between monomer units?
ester
Which raw material serves as source for most polymers?
crude oil
What is an amine group?
NH2
Which synthetic polymer has two forms (crystal and expandable)?
PS
Which synthetic polymer has two forms (crystal and expandable)?
PS
Skin, hair, muscle, and enzymes are all made of protein which is a natural polymer. What polymer?
polyamides
What is electrolysis?
a process that requires an electrical current to break water into hydrogen gas and oxygen gas
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?
a fuel cell using hydrogen operates at a higher overall efficiency than would a power plant burning hydrogen as fuel
Cellulose is classified as a…
condensation homopolymer
Sunlight may be turned directly into electricity using _____
photovoltaic cells
What is the oxidation half-reaction?
Zn –> Zn^(2+) + 2e-
Whenever a substance is oxidized…
another substance must be reduced
Where does reduction take place in a fuel cell?
at the cathode
