Chapter 8 - Energy From Electron Transfer Flashcards Preview

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Flashcards in Chapter 8 - Energy From Electron Transfer Deck (32)
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1
Q

What is a battery?

A

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

2
Q

What are galvanic cells?

A

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

3
Q

What are electrolytic cells?

A

cells that convert electrical energy to chemical energy

4
Q

What is electricity?

A

the flow of electrons

5
Q

What are the parts to a full reaction?

A

half-reactions

  1. oxidation
  2. reduction
6
Q

What is oxidation?

A

the loss of an electron

7
Q

What is reduction?

A

the addition of an electron

8
Q

OILRIG

A

Oxidation Is Loss, Reduction Is Gain

9
Q

How do you make electricity?

A
  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
10
Q

What are electrical conductors?

A

sites of reactions

  1. cathode
  2. anode
11
Q

What is a cathode?

A

where reduction occurs, electrons are gained

12
Q

What is an anode?

A

where oxidation occurs, electrons are lost

13
Q

What is voltage?

A

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

14
Q

What is a salt bridge?

A

transfers ions, completes circuit between two solutions

15
Q

What are desirable properties in a battery?

A
  • high voltage (energy efficient)
  • cheap
  • long lasting
  • safe handling/disposal
  • small/light
16
Q

What is a lead-acid battery?

A

true batter that consists of a series of 6 cells

  • anode: Pb, cathode: PbO2
  • stores electrical energy
17
Q

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

A

advantages:

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

disadvantages:

  • heavy
  • toxic
18
Q

What are ways we could improve batteries?

A
  1. Safer Disposal- phase out mercury/lead
  2. Lighter/More Dependable
  3. Rechargeable- Nickel-metal hydride, lithium-ion, replace alkaline
  4. Efficiency
19
Q

What are hybrid cars?

A

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)
20
Q

What are fuel cells?

A

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%)

21
Q

What are the advantages of fuel cell cars?

A
  • 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
22
Q

What are the disadvantages of fuel cell cars?

A
  • slower reaction- not as much power in shorter amount of time
  • catalysts are expensive
23
Q

What are the chemical changes in a fuel cell?

A

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)

24
Q

Energy output of fuel cells

A

143 kJ/g

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

25
Q

Sources of H2

A
  • 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

26
Q

H2 storage and transplant

A
  • 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!
27
Q

What are possible options for H2 storage?

A

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

28
Q

What are photovoltaics?

A

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?
29
Q

What are semiconductors?

A

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
30
Q

Development of semiconductors

A
  • 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)
31
Q

Economics of Energy

A

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

32
Q

Installation of solar energy

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