SAC 1 - Content Crucial for revision Flashcards
(56 cards)
1
Q
Define Fuel
A
- releases heat energy in combustion reaction and stores chemical energy
2
Q
What are fossil fuels?
A
- derived from fossils remains of living organisms
- found in earth’s crust formed through decompositions under anaerobic intense heat and pressure that alter chemical structure over millions of years
- non-renewable
3
Q
What are the type of fossil fuels?
A
Coal, Natural Gas and Petrol
4
Q
Define Coal
A
- most abundant fossil fuel mined in ground and formed by gradual chemical changes to decomposing wood and plant material where carbon content increases
5
Q
Black coal vs brown coal
A
Higher energy content because higher carbon content
6
Q
Define Natural Gas
A
Methane (90%) ethane, propane, CO2 and nitrogen
7
Q
Define Coal Seam Gas
A
- found in earth’s crust deposits
- extracted by drilling and fracking (inject liquid at high pressure into coal to force open fissures)
8
Q
Crude Oil
A
- mixture of hydrocarbons
- separated into different hydrocarbons through fractional distillation
- often contaminated with sulfur
9
Q
Environmental constraints of fossil fuels
A
- drilling/mining disrupts natural landscape and natural water table if spills occur
- produce CO2 contributing to enhanced greenhouse effect
- contamination with sulfur compounds can cause acid rain through SO2 emissions
10
Q
What are some organic sources of glucose?
A
Sugarcane, soya beans and corn
11
Q
Environmental and sustainability considerations of biofuels
A
- land and water supplies are limited in some countries and biofuel production should not reduce amount of food available
- to reduce greenhouse gas emissions, immense land for growing required
- non-renewable fuels used in transport
12
Q
Glucose
A
Simple carbohydrate and primary source of energy
13
Q
Photosynthesis
A
plants, algae, bacteria convert light energy from sun into chemical energy in form of glucose.
14
Q
Activation energy
A
Minimum energy required to break bonds in reactants (larger activation energy indicates stronger bonds)
15
Q
Exothermic reactions
A
releases energy to the environment, energy required to break bonds is less than energy released when new bonds form
16
Q
Endothermic reactions
A
- absorbs energy
- energy required to break bonds is greater than the energy released when new bonds form
17
Q
Reactants
A
Consumed during a reaction
18
Q
Reagents
A
Not neccersarily consumed e.g. a catalyst
19
Q
Combustion of methane
A
- 10 times more potent than CO2
- combustion of methane to produce carbon dioxide in some instances better
20
Q
NET amount formula
A
Amount produced - amount consumed
21
Q
Specific heat capacity
A
amount of heat energy required to raise the temperature of 1g of a substance by 1 degree.
22
Q
Limitations of water method
A
- low accuracy due to large amount of heat loss to surroundings
- mass of water being heated will change due to evaporation
- not all fuels are available in form to be safely combusted
23
Q
Primary Cells
A
- cannot be recharged
- fixed quantity of stored reactants
- operate in closed environments
24
Q
Consideration of Galvanic Cells
A
- environment species that may interfere with the cell function
- products/reactants/malfunctions dangerous
- environmental impacts e.g. heavy metal
- ability to source material
25
Purpose of an inert electrode
- used to conduct current
- non-reactive
- solid
- conduct electricity
26
Features of the electrochemical series
- only valid under SLC
- 25 degrees
- 100kPa
- 1M concentration
27
Limitations of the Electrochemical series
- doesn't indicate reaction rate
- only valid under SLC
28
What is a Galvanic Cell?
cell that converts chemical energy to electrical energy
- must have two half cells so that electrons are forced to move through external circuit and produce electrical energy rather than heat energy
29
Observation at anode
- decrease mass, increase colour
30
Salt bridge
- completes circuit
- provides free moving ions to compensate for those lost/gained
- must be soluble, ionic, not interfere, not form a precipitate
31
Fuel Cells
Cell that continuously converts chemical energy into electrical energy via redox reaction where reactants continuously supplied.
32
Porous Electrode
Material with many holes used in a fuel cell to maximise the ability of gaseous reactants to come into contact with the electrolyte
33
Fuel Cell efficiency
- more efficient than power stations at converting chemical energy to electrical energy (40-60% compared to 30-36%)
- reduces greenhouse emissions, remove reliance on fossil fuels
34
Similarities between fuel and galvanic cells
- convert chemical to electrical energy
- cells separated
- contains electrolyte
- produce voltage
- connected to a load (something that consumes electrical energy)
- can be stacked
35
Differences between fuel and galvanic cells
- reactants continuously supplied from an external source
- open systems often involving gaseous reactants
- membranes often used as electrolytes, polymer layer that conducts H+ ions known as proton electrolyte membrane
- electrodes are porous to improve contact between gas and electrolyte. (size allows certain molecules, increase surface area, catalysts, increase rate of reaction)
36
Acidic conditions
- greater concentration of H+ ions
37
Advantages of fuel cells
- lower emissions of harmful sulfur-nitrogen containing compounds compared to direct combustion
- low maintenance and running costs
- quiet
- no direct CO2 emissions from hydrogen fuel cells.
- greater efficiency as less waste heat/energy conversions
38
Disadvantages of fuel cells
- storage and safety issues associated with highly explosive hydrogen fuel
- expensive to manufacture
- require new infrastructure for hydrogen fuel
- not as convenient as batteries.
39
Faraday's First Law
The amount of electrical charge carried by a galvanic cell is directly proportional to the mass of anode lost/fuel used or mass gained by the cathode.
40
Feedstock
Raw material used for producing another product
- renewable feedstocks can increase sustainability
41
Sustainable
Produced at a rate greater or equal to the consumption rate without compromising future generations
42
Factors contributing to the energy efficiency of fuel cells
- catalysts
- electrode porosity and nanomaterials
- combined heat and power
- hybrid systems
- polymer membrane electrolytes
- operating conditions
- durability
43
Catalysts
- increase rate of reaction
- reduce amount of time for energy to escape system increasing efficient
- effective catalysts are nonrenewable and expensive
44
Electrode porosity and nanomaterials
- porous allows diffusion of gaseous reactants
- smaller + more numerous pores provide greater surface area
- increases contact between reactants and catalysts
45
Combined heat and power
Heat, a by product of fuel cells is captured and used to heat other things.
46
Hybrid systems
- combining fuel with another energy system
- allows excess energy to be stored minimising energy loss
47
Polymer membrane electrolytes
Maximize speed of ion movement
more resistant to temperature changes
- expensive and derived from crude oil
48
Operating conditions
- higher temperatures and pressures increase rate of reaction
- maintaining high temperatures requires large amounts of energy
49
Durability
Increasing lifespan of fuel cell will increase long term efficiency
50
First generation feedstock source
- edible crops e.g wheat/sugarcane
- intensive farming required to meet demand, potentially damaging soil
- competes with valuable food sources
51
Second generation feedstock source
non-food crops e.g grass
- waste readily available
- difficult to convert biomass to usable fuels.
52
Function of Seperator
- separates reactants
- allows for the flow of ions
53
Disadvantage of hydrogen as a fuel
- lack of refueling stations
- storage of gas under high pressure.
54
When would a galvanic cell stop?
- one of ion in salt bridge depleted
- electrodes no longer immersed in solution
- wires are disconnected
55
Top of energy diagram is
Transition energy
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