Chapter 8 - Energy From Electron Transfer Flashcards Preview

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

What is a battery?

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

2

What are galvanic cells?

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

3

What are electrolytic cells?

cells that convert electrical energy to chemical energy

4

What is electricity?

the flow of electrons

5

What are the parts to a full reaction?

half-reactions
1. oxidation
2. reduction

6

What is oxidation?

the loss of an electron

7

What is reduction?

the addition of an electron

8

OILRIG

Oxidation Is Loss, Reduction Is Gain

9

How do you make electricity?

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

What are electrical conductors?

sites of reactions
1. cathode
2. anode

11

What is a cathode?

where reduction occurs, electrons are gained

12

What is an anode?

where oxidation occurs, electrons are lost

13

What is voltage?

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

14

What is a salt bridge?

transfers ions, completes circuit between two solutions

15

What are desirable properties in a battery?

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

16

What is a lead-acid battery?

true batter that consists of a series of 6 cells
-anode: Pb, cathode: PbO2
-stores electrical energy

17

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

advantages:
-long lasting
-rechargeable
-power starter (ex. lights, radio, etc)
-alternator recharges

disadvantages:
-heavy
-toxic

18

What are ways we could improve batteries?

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

19

What are hybrid cars?

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

What are fuel cells?

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

What are the advantages of fuel cell cars?

-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

What are the disadvantages of fuel cell cars?

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

23

What are the chemical changes in a fuel cell?

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

Energy output of fuel cells

143 kJ/g

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

25

Sources of H2

-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

H2 storage and transplant

-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

What are possible options for H2 storage?

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

What are photovoltaics?

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

What are semiconductors?

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

Development of semiconductors

-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

Economics of Energy

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

32

Installation of solar energy

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