Reactivity 1.3

Question 1

Combustion reaction (endo/exo)

Answer 1

Exothermic

Question 2

Standard enthalpy of combustion

Answer 2

Enthalpy change when one mole of substance in its standard state combusts completely in oxygen under standard conditions

Question 3

Specific energy of a fuel formula

Answer 3

Energy released from the fuel / mass of fuel consumed

Question 4

Specific energy of a fuel units

Answer 4

kJ kg-1

Question 5

Fossil fuel formation

Answer 5

Formed from buried organisms that have undergone reduction under pressure

Question 6

Main fossil fuels

Answer 6

Coal, crude oil, natural gas

Question 7

Crude oil

Answer 7

Mixture of hydrocarbons (mainly alkanes)

Question 8

Natural gas pros/cons

Answer 8

• Clean, easily transportable, higher specific energy density
• Global warming, limited lifespan, uneven distribution (fracking)

Question 9

Oil pros/cons

Answer 9

• Easily transported, convenient, feedstock
• Global warming/acid rain, limited lifespan, risk of pollution

Question 10

Coal pros/cons

Answer 10

• Present in large quantities, can be converted to synthetic liquid/gases, energy dense, longer lifespan
• Global warming/acid rain, not easily transported, dangerous mining, dirty

Question 11

Greenhouse effect

Answer 11

Incoming radiation from the sun is UV/visible, most is absorbed, some reflected as IR. Greenhouses gases absorb some radiated infrared heat and reradiate it to the Earth.

Question 12

Why do greenhouse gases absorb infrared radiation?

Answer 12

Molecules increase their vibrational state when thy absorb infrared radiation. Three of their vibrational modes are IR active and the dipole changes as they vibrate.

Question 13

Which vibrational mode of carbon dioxide does not produce a change in dipole and is IR inactive?

Answer 13

Symmetrical stretch as the molecule remains symmetrical.

Question 14

Which vibrational modes of carbon dioxide produce a change in dipole and are IR active?

Answer 14

Asymmetrical stretch and two symmetrical bends

Question 15

How can you find the CO2 equivalent of a greenhouse gas?

Answer 15

By multiplying its 100 year global warming potential (GWP)

Question 16

Carbon footprint

Answer 16

Total amount of greenhouse gases produced during human activities

Question 17

Largest contributing factor of carbon footprint

Answer 17

Supply and distribution of goods

Question 18

Photosynthesis process

Answer 18

Chlorophyll in plants absorb the energy of sunlight (0.6% of total that reaches earth) and convert water/co2 into glucose (carbohydrates)/ (light to chemical energy)

Question 19

Photosynthesis endo/exo

Answer 19

It is endothermic and enthalpy change for every mole of glucose formed is +2816 kJmol

Question 20

How can energy from biomass be obtained?

Answer 20

Burned directly

Question 21

How can liquid fuel be obtained from biomass?

Answer 21

Fermentation

Question 22

Gasohol

Answer 22

Mixture of 10% ethanol and 90% gasoline.

Question 23

Biomass fuel cons/pros

Answer 23

• Renewable, low carbon footprint, safe production
• Uses up land, may pollute water, remove nutrients from soil, small scale production

Question 24

Hydrogen fuel cell

Answer 24

Energy produced during combustion of hydrogen in oxygen to form water is given out as electricity. It can give out a continuous supply of electricity.

Question 25

Hydrogen fuel cell unique to rechargable batteries

Answer 25

Do not need an external source of electricity and are non polluting as the only product is water

Question 26

Overall reaction in a hydrogen fuel cell (alkaline and acidic)

Answer 26

2H2 (g) + 02 (g) -> 2H20 (l)

Question 27

Anode equation alkaline hydrogen fuel cell

Answer 27

H2 + 2OH- -> 2H2O + 2e-

Question 28

Cathode equation alkaline hydrogen fuel cell

Answer 28

O2 + 2H2O +4e- -> 4OH-

Question 29

Types of electrochemical cells

Answer 29

Voltaic -> redox occur spontaneously (chemical - electrical)
Electrolytic cell -> Electrical energy is used to cause reaction (electrical - chemical)

Question 30

Methanol fuel cell

Answer 30

When fuels other than hydrogen can be used in fuel cells to convert chemical energy directly to electrical energy

Question 31

Anode equation acidic hydrogen fuel cell

Answer 31

H2 -> 2H+ + 2e-

Question 32

Cathode equation acidic hydrogen fuel cell

Answer 32

O2 + 4H+ + 4e- -> 2H2O

Question 33

Anode equation methanol fuel cell

Answer 33

CH3OH + H2O -> CO2 + 6H+ + 6e-

Question 34

Cathode equation methanol fuel cell

Answer 34

3O2 + 12H+ +12e- -> 6H2O