Chapter 2 - Carbon Based Fuels

Question 1

Endothermic

Answer 1

a reaction that absorbs energy from its surroundings in the form of heat. Has a positive enthalpy change (ΔH)

Question 2

Exothermic

Answer 2

reaction that releases energy in the form of heat. Negative enthalpy change (-ΔH)

Question 3

Activation energy

Answer 3

the energy required to break the bonds of the reactants so that a reaction can proceed

Question 4

Fuels

Answer 4

stored chemical energy that can be released easily

Question 5

Enthalpy

Answer 5

the chemical energy of a substance. also known as heat content

Question 6

Enthalpy change

Answer 6

the exchange of heat energy between the system and its surroundings under constant pressure. OR difference in chemical energy of products compared to reactants

Question 7

Molar Enthalpy

Answer 7

the enthalpy of a substance given
per mole

Question 8

Thermochemical equation

Answer 8

when the value of ΔH is added to a balanced equation

Question 9

Renewable fuels

Answer 9

a fuel that can be replenished naturally at the rate that it is being consumed

Question 10

Non-Renewable fuels

Answer 10

fuel that cannot be replenished at the rate which it is consumed. E.g. coal, oil, natural gas

Question 11

Fossil Fuels

Answer 11

Non-Renewable fuels. Was formed over millions of years buried underground, in the geological past from the remains of living organisms

Question 12

Petrol (crude oil/petroleum)

Answer 12

mixture of hydrocarbon molecules (mostly from homologous series of alkanes). The useful compounds in crude oil (useless in itself) are separated by fractional distillation which can be treated to produce specific products through chemical processes

Question 13

Natural Gas

Answer 13

fossil fuel found in deposits of earths crust. mainly composed of methane, with small amounts of ethane, propane

Question 14

Biofuels

Answer 14

fuels derived from plant materials (living matter) such as grains, sugar cane, vegetable waste, vegetable oil. can be used alone or blended with petrol/diesel. seen as carbon neutral due to photosynthesis

Question 15

Biogas

Answer 15

gas released in the breakdown of organic waste by anaerobic bacteria. break complex molecules (carbs, proteins) into simple molecular compounds, co2 and methane

Question 16

Biodiesel

Answer 16

produced from triglycerides in animal fats or plant oil. The triglycerides react with methanol in transesterification reaction to form biodiesel

Question 17

Photosynthesis

Answer 17

green plants use energy from the sun for photosynthesis, the conversion of carbon dioxide and water to glucose and oxygen. 6CO2 + 6H2O → C6H12O6 + 6O2 ΔH=+2803kJ (endothermic)

Question 18

Cellular Respiration

Answer 18

plants and animals use cellular respiration to oxidise glucose to obtain energy. reverse of photosynthesis. C6H12O6 + 6O2 –> 6CO2 + 6H2O ΔH=-2803kJ

Question 19

Bioethanol

Answer 19

produced from glucose and other sugars in a fermentation process. C6H12O6(aq) –> 2CH3CH2OH(aq) + 2CO2(g)

Question 20

Distillation (in bioethanol production)

Answer 20

a process that utilises the different boiling points of the liquids to separate the two liquids. the energy required to distil bioethanol means that it is not carbon neutral. ethanol has lower boiling point than water

Question 21

Fermentation

Answer 21

a natural process in which an organism converts a carbohydrate such as starch or sugar into an alcohol

Question 22

E10 fuel

Answer 22

a blend of petrol and 10% bioethanol. compared to petrol, E10 has: lower energy density (46kJ), cheaper, cleaner combustion, can be a renewable fuel, lower net CO2 emissions, generally safer production
Combustion of ethanol:
C2H5OH(l) + 3O2(g) —> 2CO2(g) + 3H2O(l) ΔH= -1360kJ

Question 23

Combustion reactions

Answer 23

exothermic, reactant combines with oxygen to produce oxides (oxidation reaction). The combustion of a hydrocarbon produces carbon dioxide and water, provided there is enough oxygen present

Question 24

Complete combustion

Answer 24

occurs when oxygen is plentiful, produces carbon dioxide and water

Question 25

Incomplete combustion

Answer 25

occurs when oxygen supply is limited so not all of the carbon can be converted into carbon dioxide, produces carbon monoxide instead

Question 26

Transesterification

Answer 26

the process of exchanging the organic functional group of an ester with the organic group of an alcohol

Question 27

Thermal energy

Answer 27

energy contained within a system that is responsible for its temperature