Chapter 8 - Energy From Electron Transfer

Question 1

What is a battery?

Answer 1

stored energy that is converted from chemical (potential) to electrical (kinetic) energy

Question 2

What are galvanic cells?

Answer 2

cells that convert chemical energy to electrical energy (ex. normal battery)

Question 3

What are electrolytic cells?

Answer 3

cells that convert electrical energy to chemical energy

Question 4

What is electricity?

Answer 4

the flow of electrons

Question 5

What are the parts to a full reaction?

Answer 5

half-reactions

1. oxidation
2. reduction

Question 6

What is oxidation?

Answer 6

the loss of an electron

Question 7

What is reduction?

Answer 7

the addition of an electron

Question 8

OILRIG

Answer 8

Oxidation Is Loss, Reduction Is Gain

Question 9

How do you make electricity?

Answer 9

1. separate the half-reactions
2. connect with a wire
3. on way for reaction to go: electrons run through wire
   - -> electron flow = electrical current

Question 10

What are electrical conductors?

Answer 10

sites of reactions

1. cathode
2. anode

Question 11

What is a cathode?

Answer 11

where reduction occurs, electrons are gained

Question 12

What is an anode?

Answer 12

where oxidation occurs, electrons are lost

Question 13

What is voltage?

Answer 13

the ease of anode release/cathode absorption –> bigger difference = greater voltage
units: volts

Question 14

What is a salt bridge?

Answer 14

transfers ions, completes circuit between two solutions

Question 15

What are desirable properties in a battery?

Answer 15

• high voltage (energy efficient)
• cheap
• long lasting
• safe handling/disposal
• small/light

Question 16

What is a lead-acid battery?

Answer 16

true batter that consists of a series of 6 cells

• anode: Pb, cathode: PbO2
• stores electrical energy

Question 17

What are the advantages/disadvantages of lead-acid batteries?

Answer 17

advantages:

• long lasting
• rechargeable
• power starter (ex. lights, radio, etc)
• alternator recharges

disadvantages:

• heavy
• toxic

Question 18

What are ways we could improve batteries?

Answer 18

1. Safer Disposal- phase out mercury/lead
2. Lighter/More Dependable
3. Rechargeable- Nickel-metal hydride, lithium-ion, replace alkaline
4. Efficiency

Question 19

What are hybrid cars?

Answer 19

Two engines (gas and NiMH/Li-ion)

• environmentally friendly, less pollutants
• range of gas engine
• other combos possible
• better gas mileage (in-city better than highway)

Question 20

What are fuel cells?

Answer 20

chemical energy —> electrical energy (no fire/explosion)
BIG difference from batteries
-fuel and oxidant supplied
-“waste” expelled continuously
-half reactions are separate
-force H thru membrane (electrons thru wire)
-no flame, no solids needed
-little heat (efficient, less lost energy)
-product = water (environmentally friendly)
-unused H2 or O2 can be put back thru system
-40-45% efficient (compared to gasoline: 20-30%)

Question 21

What are the advantages of fuel cell cars?

Answer 21

• no nitrogen oxides
• low/no CO2 emissions
• H2, methanol–> renewable resource? (biological sources)
• Engine: no/fewer moving parts = less/easier repair, longer lasting
• No recharging: fuel continuously provided, faster than recharging a battery

Question 22

What are the disadvantages of fuel cell cars?

Answer 22

• slower reaction- not as much power in shorter amount of time
• catalysts are expensive

Question 23

What are the chemical changes in a fuel cell?

Answer 23

H2 + 1/2 O2 –> H2O
Anode reaction: (Oxidation half-reaction)
H2(g) –> 2 H+(aq) + 2 e–
Cathode reaction: (Reduction half-reaction)
½ O2(g) + 2 H+(aq) + 2 e- –> H2O(l)

Question 24

Energy output of fuel cells

Answer 24

143 kJ/g

compared to…
coal: 30 kJ/g
gas: 46 kJ/g
natural gas: 54 kJ/g

Question 25

Sources of H2

Answer 25

• most plentiful element (93%)
• Very reactive (tied up in compounds)
• Must be extracted

From water?
572 kJ + 2H2O –> 2H2 + O2
-where do you get the energy?

From Methane/water?
165 kJ + CH4 + 2H2O –> 4H2 + CO2
-need a catalyst to be more efficient

Question 26

H2 storage and transplant

Answer 26

• 12 L/g (approx 3 gal)
• cylinders: heavy/pressurized
• transport –> need more energy to transport the heavy H2
• liquify? –> would need to be -253 degrees C
• explosive!

Question 27

What are possible options for H2 storage?

Answer 27

1) absorb onto C – Heat to release
2) React to make metal hydrides
2 Li + H2 –> 2 LiH
–>Reverse with water: LiH + H2O –> H2 + LiOH
3) Making ammonia:
N2 + 3H2 –> 2NH3 + energy
–>Reverse reaction: 2NH3 + energy –> N2 + 3H2
4) Storage in Nanotubes: tubes of C atoms, reusable, $$$
5) Photovoltaics: solar power

Question 28

What are photovoltaics?

Answer 28

Solar Power

• sun –> lots of energy to earth
• renewable
• light/heat, not useful for work
• solar energy —photovoltaic cell—> electricity
• -> use this energy for H2 production?

Question 29

What are semiconductors?

Answer 29

only conduct under specific conditions (ex. photon of right wavelength collides)

• silicon (4A): primary component of photovoltaic cells
  
  • photon of 1100nm will knock electrons off
  • visible light: more than enough energy
• problems: expensive refinement, low efficiency (max 28%) –> but energy is free/unlimited

Question 30

Development of semiconductors

Answer 30

• non-crystalline silicon –> decreased $$, increased efficiency
• “doping” silicon: combine with other materials
  
  • ->ex. As (5A): one more outer electron (n-type, “negative”), Ga (3A): one less outer electron (p-type, “positive”)
• easier to make current (lower energy photons, sandwich n-/p-type connected by wire)

Question 31

Economics of Energy

Answer 31

Solar: cost dropping
Fossil Fuel: cost increasing
Solar Investments: increasing, currently 1% of global power, favored over nuclear

Question 32

Installation of solar energy

Answer 32

Low-maintenance
Build anywhere
-Lots of space
-Isolated areas
-Undeveloped areas
-No “network”