r1.3 energy from fuels

Question 1

what is a combustion reaction?

Answer 1

a combustion reaction involves two important reactants: fuel and oxygen gas
these reactions are highly exothermic since the products are energetically more stable than the reactant fuel and oxygen gas

Question 2

what happens when reactive metals react with oxygen?

Answer 2

when reactive metals combine with oxygen they can produce tremendous amounts of energy, both in the form of heat and light

Question 2

what happens when less reactive metals react with oxygen?

Answer 2

less reactive metals (eg. iron, copper, silver) also combine with oxygen to form their own metallic oxides. we often describe these chemical reactions as rusting or tarnishing

Question 3

what happens when non-metals react with oxygen?

Answer 3

many non-metals react with oxygen to form non-metallic oxides. these oxides do not have fixed ratios, so these combustion reactions can produce several different product oxides for the same non-metal fuel

Question 4

what happens when organic compounds react with oxygen?

Answer 4

all organic compounds, especially hydrocarbons, as well as alcohols, easily undergo complete combustion reactions that produce only carbon dioxide and water

Question 5

what are fossil fuels?

Answer 5

coal, oil, and natural gas are fossil fuels. fossil fuels were formed by the reduction of biological compounds that contain carbon, hydrogen, nitrogen, sulfur and oxygen. they were formed over millions of years from the remains of dead organisms

Question 6

what is the composition of coal?

Answer 6

• solid
• mainly carbon, traces of hydrogen, oxygen, nitrogen, sulfur, and metals

Question 7

what is the composition of crude oil?

Answer 7

• liquid
• mixture of medium to long chain hydrocarbons, traces of sulfur, nitrogen, oxygen, and metals

Question 8

what is the composition of natural gas?

Answer 8

• gas
• mostly methane, traces of other small hydrocarbons, water, and carbon dioxide

Question 9

how do you separate crude oil?

Answer 9

the components of fossil fuel mixtures can be separated by their boiling point in a process called fractional distillation

Question 10

what is the specific energy of a fuel?

Answer 10

the specific energy of a fuel is a measure of the amount of energy produced in a complete combustion reaction per unit mass of the fuel. coal produces the least energy per unit mass, and natural gas the most energy per unit mass

Question 11

how much carbon dioxide does coal produce?

Answer 11

coal, consisting mainly of carbon, produces a high quantity of carbon dioxide during its combustion

Question 12

how much carbon dioxide does crude oil produce?

Answer 12

crude oil, a mixture of longer chain hydrocarbons, produces carbon dioxide and water during combustion. since there are two products formed, the amount of carbon dioxide produced per unit of energy released is lower than coal

Question 13

how much carbon dioxide does natural gas produce?

Answer 13

natural gas, consisting mostly of methane, also produces carbon dioxide and water. natural gas has a lower carbon to hydrogen ratio compared to longer hydrocarbon chains, resulting in less carbon dioxide released per unit energy compared to crude oil

Question 14

what are the advantages of coal?

Answer 14

• relatively cheap
• abundant
• long lifespan
• can be converted into liquid fuels and gases
• relatively safe
• products from the combustion of coal have other uses

Question 15

what are the disadvantages of coal?

Answer 15

• finite
• impurities, higher amounts of oxygen required, likely incomplete combustion
• produces alot of pollution
• environmental issues
• difficult to transport
• issues around mining
• potentially radioactive

Question 16

what are the advantages of crude oil?

Answer 16

• easy to store and transport
• impurities can be easily removed
• high energy density
• easily processed

Question 17

what are the disadvantages of crude oil?

Answer 17

• finite
• produces alot of pollution
• environmental issues
• uneven worldwide distribution
• oil spills
• safety issues around drilling

Question 18

what are the advantages of natural gas?

Answer 18

• cheapest of the fossil fuels
• easy to store and transport
• high specific energy
• relatively clean

Question 19

what are the disadvantages of natural gas?

Answer 19

• finite
• produces alot of pollution
• global warming
• expensive and time intensive
• expensive to store
• safety issues around storage in pressurised containers

Question 20

what is the greenhouse effect?

Answer 20

the greenhouse effect is a phenomenon that occurs when certain gases, such as carbon dioxide, methane, water vapour or nitrogen oxides, absorb IR radiation that has been emitted from the earth’s surface after it has been heated by the suns rays and trap it within the earth’s atmosphere
since the combustion of fossil fuels releases carbon dioxide gas, a slightly higher proportion of the solar energy is trapped within the atmosphere, leading to higher average global temperatures

Question 21

what are the properties of a primary voltaic cell?

Answer 21

• converts chemical energy to electrical energy
• mostly irreversible reactions
• redox reactions
• finite supply of fuel
• contains metal compounds

Question 22

what are the properties of a secondary cell?

Answer 22

• converts chemical energy to electrical energy
• reversible reactions
• redox reactions
• finite supply of fuel
• lithium ion battery

Question 23

what are the properties of a fuel cell?

Answer 23

• converts chemical energy to electrical energy
• reversible reactions
• redox reactions
• continuous supply of fuel
• example is DMFC

Question 24

what is a fuel cell?

Answer 24

a fuel cell is an electrochemical cell in which a fuel donates electrons at one electrode (anode) and oxygen gains electrons at the other electrode (cathode) these cells are becoming more common in the automotive industry to replace petrol or diesel engines

Question 25

how do fuel cells work?

Answer 25

as the fuel enters the cell, it becomes oxidised which sets up a potential difference within the cell different electrolytes and fuels can be used to set up different types of fuel cells an important cell is the hydrogen-oxygen fuel cell

Question 26

what does a hydrogen-oxygen fuel cell work?

Answer 26

the fuel cell consists of: - a reaction chamber with separate inlets for hydrogen and oxygen gas - anode which has a platinum based surface - an outlet for water - the proton exchange membrane (PEM) which selectively allows hydrogen ions to diffuse between the cathode and anode

Question 27

what are the equations in a hydrogen-oxygen fuel cell?

Answer 27

2H₂ (g) -> 4H⁺ (aq) + 4e⁻ O₂ (g) + 4H⁺ (aq) + 4e⁻ -> 2H₂O (l) overall redox reaction: 2H₂ (g) + O₂ (g) -> 2H₂O (l) the reaction is a spontaneous and exothermic reaction

Question 28

how is the hydrogen in a hydrogen-oxygen fuel cell produced?

Answer 28

1. the electrolysis of water, the electricity sourced from renewable energy sources 2H₂O (l) -> 2H₂ (g) + O₂ (g) 2. steam reforming of hydrocarbons which uses natural gas, gasified coal, diesel, ect. as the hydrocarbon source

Question 29

what are the advantages of hydrogen fuel cells?

Answer 29

- water is the only reaction product, environmental advantages - the reaction takes place at room temperature - no harmful oxides of nitrogen produced - have been used in space, where product can be used as drinking water

Question 30

what are the disadvantages of hydrogen fuel cells?

Answer 30

- hydrogen is highly flammable - thick walled cylinders and pipes are needed, economic impacts - hydrogen relies on a non-renewable resource - hydrogen has high specific energy

Question 31

what is a direct methanol fuel cell?

Answer 31

the methanol fuel cell works in a similar fashion to the hydrogen fuel cell. the main difference is that the fuel or source of hydrogen ions is methanol rather than hydrogen

Question 32

what does a DMFC consist of?

Answer 32

- a reaction chamber with separate inlets for methanol and oxygen - the anode requires a catalyst such as ruthernium or palladium - outlets for the carbon dioxide and water products - an electrolyte, typically a proton exchange membrane

Question 33

what are the half equations in a DMFC?

Answer 33

CH₃OH (aq) + H₂O (l) → CO₂ (g) + 6H⁺ (aq) + 6e⁻ O₂ (g) + 4H⁺ (aq) + 4e⁻ → 2H₂O (l) the overall equation is: CH₃OH (aq) + 1½ O₂ (g) → CO₂ (g) + 2H₂O (l)

Question 34

what are the advantages of a DMFC?

Answer 34

- methanol is easier to store - membrane has longer life span - methanol can be produced from renewable resources - methanol has a greater energy density than hydrogen and lithium ion batteries

Question 35

what are the disadvantages of a DMFC?

Answer 35

- methanol is very toxic and highly flammable - fuel cell produces lower voltage - low efficiancy - requires a more highly efficient catalyst - produces the greenhouse gases

Question 36

what are renewable resources?

Answer 36

renewable resources will not run out in the foreseeable future because they can be replaced over a relatively short period of time they can be considered sustainable as they can be produced at the same rate, or faster, than they are being used

Question 37

what are non-renewable resources?

Answer 37

non-renewable resources will run out in the foreseeable future as there are limited supplies. they are not a sustainable resource